LM3697 High-Efficiency Three-String White LED Driver 1 Features 3 Description

LM3697 High-Efficiency Three-String White LED Driver 1 Features 3 Description
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LM3697
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LM3697 High-Efficiency Three-String White LED Driver
1 Features
3 Description
•
The LM3697 11-bit LED driver provides highperformance backlight dimming for 1, 2, or 3 series
LED strings while delivering up to 90% efficiency. The
boost converter with integrated 1-A, 40-V MOSFET
automatically adjusts to LED forward voltage to
minimize headroom voltage and effectively improve
LED efficiency.
1
•
•
•
•
•
•
•
•
•
•
•
•
Drives Three Parallel High-Voltage LED Strings
for Display and Keypad Lighting
High-Voltage Strings Capable of up to 40-V
Output Voltage and up to 90% Efficiency
Up to 30 mA per Current Sink
11-Bit Configurable Dimming Resolution
PWM Input for Content Adjustable Brightness
Control (CABC)
Fully Configurable LED Grouping and Control
Integrated 1-A/40-V MOSFET
Adaptive Boost Output to LED Voltages
Selectable 500-kHz and 1-MHz Switching
Frequency
Four Configurable Overvoltage Protection
Thresholds (16 V, 24 V, 32 V, and 40 V)
Overcurrent Protection
Thermal Shutdown Protection
29-mm2 Total Solution Size
The LM3697 is a high-efficiency three-string power
source for backlight or keypad LEDs in smart-phone
handsets. The high-voltage inductive boost converter
provides the power for three-series LED strings for
display backlight and keypad functions (HVLED1,
HVLED2 and HVLED3).
An additional feature is a pulse width modulation
(PWM) control input for content adjustable backlight
control, which can be used to control any highvoltage current sink.
The LM3697 is fully configurable via an I2Ccompatible interface. The device operates over a
2.7-V to 5.5-V input voltage range and a −40°C to
85°C temperature range.
2 Applications
•
•
Device Information(1)
Power Source for Smart Phone Illumination
Display, Keypad and Indicator Illumination
ORDER NUMBER
LM3697YFQ
PACKAGE
BODY SIZE (MAX)
DSBGA (12)
1.64 mm x 1.29 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
space
space
space
Simplified Schematic
L
D1
Boost Efficiency
VOUT up to 40V
VIN = 2.7V to 5.5V
CIN
Three String, L=22µH, 1MHz
COUT
92%
IN
SCL
HWEN
PWM
LM3697
SDA
SW
PGND
90%
OVP
HVLED1
HVLED2
HVLED3
88%
EFFICIENCY (%)
VIN
86%
84%
82%
80%
78%
3s3p
4s3p
5s3p
6s3p
7s3p
76%
74%
72%
70%
2.5
3
3.5
4
4.5
5
5.5
VIN (V)
C049
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
LM3697
SNOSCS2C – NOVEMBER 2013 – REVISED OCTOBER 2015
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Table of Contents
1
2
3
4
5
6
7
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
3
4
6.1
6.2
6.3
6.4
6.5
6.6
6.7
4
4
4
4
5
6
7
Absolute Maximum Ratings ......................................
ESD Ratings..............................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics ..........................................
Timing Requirements ................................................
Typical Characteristics ..............................................
Detailed Description .............................................. 8
7.1
7.2
7.3
7.4
Overview ................................................................... 8
Functional Block Diagram ......................................... 8
Feature Descriptions ................................................. 9
Device Functional Modes........................................ 12
7.5 Register Maps ......................................................... 16
8
Application and Implementation ........................ 20
8.1 Application Information............................................ 20
8.2 Typical Applications ................................................ 20
8.3 Initialization Set Up ................................................. 30
9 Power Supply Recommendations...................... 31
10 Layout................................................................... 32
10.1 Layout Guidelines ................................................. 32
10.2 Layout Example .................................................... 35
11 Device and Documentation Support ................. 36
11.1
11.2
11.3
11.4
11.5
11.6
Device Support......................................................
Related Documentation .......................................
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
36
36
36
36
36
36
12 Mechanical, Packaging, and Orderable
Information ........................................................... 36
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision B (April 2014) to Revision C
Page
•
Changed format of Device Information; add footnote and "MAX" ......................................................................................... 1
•
Changed Handling Ratings table to ESD Ratings table format; move storage temp to Abs Max table................................. 4
•
Added additional Thermal Information ................................................................................................................................... 4
•
Added subsection High-Speed Mode .................................................................................................................................. 15
Changes from Revision A (December 2013) to Revision B
Page
•
Changed to new TI datasheet standards; added Handling Ratings table; added 2 ambient temperature specs to
IHVLED and one to IMATCH_HV ..................................................................................................................................................... 1
•
Changed title from Pin Configurations to Terminal Functions and all references from "pins" to "terminals" ......................... 3
•
Changed change "terminal" back to "pin" per latest documentation standard; add "Type" column to Pin Functions
table ....................................................................................................................................................................................... 3
•
Changed Timing information from Elec Char table Timing Requirements ............................................................................. 6
•
Changed Functional Description section to Detailed Description section ............................................................................. 8
•
Changed Applications Information section to Application and Implementation ................................................................... 21
•
Changed Typical Characteristics from own section into subsection of Specifications ........................................................ 23
•
Added new Power Supply Recommendations section ........................................................................................................ 31
•
Changed Layout section to include separate Layout Example ........................................................................................... 32
•
Added new Device and Documentation Support section and Mechanical, Packaging and Orderable paragraph ............. 36
Changes from Original (November 2013) to Revision A
Page
•
Added graph ......................................................................................................................................................................... 10
•
Added Auto-Frequency Threshold Settings table................................................................................................................. 10
•
Added graphic....................................................................................................................................................................... 11
•
Added captions to graphs .................................................................................................................................................... 30
2
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5 Pin Configuration and Functions
YFQ Package
12-Pin DSBGA
Bottom View
Top View
A
B
C
3
3
2
2
1
1
D
D
C
B
A
Pin Functions
PIN
TYPE
DESCRIPTION
PWM
Input
PWM brightness control input for CABC operation. PWM is a high-impedance input and cannot
be left floating, if not used connect to GND.
A2
SDA
I/O
A3
HWEN
Input
Hardware enable input. Drive this pinl high to enable the device. Drive this pin low to force the
device into a low power shutdown. HWEN is a high-impedance input and cannot be left floating.
B1
HVLED1
Input
Input pin to high-voltage current sink 1 (40 V maximum). The boost converter regulates the
minimum of HVLED1, HVLED2 and HVLED3 to VHR.
B2
SCL
Input
Serial clock connection for I2C-compatible interface.
B3
IN
Input
Input voltage connection. Bypass IN to GND with a minimum 2.2-µF ceramic capacitor.
C1
HVLED2
Input
Input pin to high-voltage current sink 2 (40 V maximum). The boost converter regulates the
minimum of HVLED1, HVLED2 and HVLED3 to VHR.
C2
GND
GND
Ground
C3
GND
GND
Ground
D1
HVLED3
Input
Input pin to high-voltage current sink 3 (40 V maximum). The boost converter regulates the
minimum of HVLED1, HVLED2 and HVLED3 to VHR.
D2
OVP
Input
Overvoltage sense input. Connect OVP to the positive terminal of the inductive boost's output
capacitor (COUT).
D3
SW
Output
NUMBER
NAME
A1
4
Serial data connection for I2C-Compatible interface.
Drain connection for the internal NFET. Connect SW to the junction of the inductor and the
Schottky diode anode.
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6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted)
(1)
MIN
MAX
UNIT
VIN to GND
−0.3
6
V
VSW, VOVP, VHVLED1, VHVLED2, VHVLED3 to GND
−0.3
45
V
VSCL, VSDA, VPWM to GND
−0.3
6
V
VHWEN to GND
−0.3
6
V
Continuous power dissipation
Internally Limited
Junction temperature (TJ-MAX)
−65
Storage temperature, Tstg
(1)
150
°C
150
°C
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
6.2 ESD Ratings
VALUE
V(ESD)
(1)
(2)
Electrostatic discharge
Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001 (1)
±2000
Charged-device model (CDM), per JEDEC specification JESD22C101 (2)
±1500
UNIT
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
6.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)
VIN to GND
VSW, VOVP, VHVLED1, VVHLED2, VHVLED3 to GND
Junction temperature (TJ)
(1)
(2)
(1) (2)
MIN
MAX
2.7
5.5
UNIT
V
0
40
V
−40
125
°C
Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ= 140°C (typical) and
disengages at TJ= 125°C (typical).
In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may
have to be derated. Maximum ambient temperature (TA-MAX) is dependent on the maximum operating junction temperature (TJ-MAX-OP =
125°C), the maximum power dissipation of the device in the application (PD-MAX), and the junction-to ambient thermal resistance of the
part/package in the application (RθJA), as given by the following equation: TA-MAX = TJ-MAX-OP – (RθJA × PD-MAX).
6.4 Thermal Information
LM3697
THERMAL METRIC
(1)
YFQ (DSBGA)
UNIT
12 PINS
RθJA
Junction-to-ambient thermal resistance
92.1
°C/W
RθJC(top)
Junction-to-case (top) thermal resistance
0.8
°C/W
RθJB
Junction-to-board thermal resistance
15.6
°C/W
ψJT
Junction-to-top characterization parameter
3.3
°C/W
ψJB
Junction-to-board characterization parameter
15.6
°C/W
RθJC(bot)
Junction-to-case (bottom) thermal resistance
n/a
°C/W
(1)
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report, SPRA953.
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6.5 Electrical Characteristics
Limits apply over the full operating ambient temperature range (−40°C ≤ TA ≤ 85°C) and VIN = 3.6 V, unless otherwise
specified. (1) (2)
PARAMETER
ISHDN
Shutdown current
ILED_MIN
Minimum LED current
TEST CONDITIONS
MIN
MAX
3
TA = 25°C
1
Full-scale current = 20.2 mA
Exponential Mapping, TA = 25°C
6
Thermal shutdown
TSD
TYP
2.7 V ≤ VIN ≤ 5.5 V, HWEN = GND
µA
µA
140
Hysteresis
UNIT
°C
15
BOOST CONVERTER
Full-scale current= 20.2 mA,
Exponential mapping,
Brightness Code = max.
IHVLED(1/2/3)
IMATCH_HV
Output current regulation
(HVLED1, HVLED2, HVLED3)
HVLED1 to HVLED2 or
HVLED3 matching (3)
Full-scale current= 20.2 mA,
Exponential mapping,
Brightness Code = max.
HVLED1 Bank A, HVLED2/3
Bank B
Exponential mapping,
auto headroom off,
PWM Off,
HVLED1/2/3 Bank A
2.7 V ≤ VIN ≤ 5.5 V
18.38
20.2
22.02
TA = 25°C
–3.4%
±2 %
3.2%
TA = 25°C
3 V ≤ VIN ≤ 4.5 V
–3.6%
TA = 25°C
3.4%
±2 %
2.7 V ≤ VIN ≤ 5.5 V
ILED = 20.2 mA
TA = 25°C
ILED = 20.2 mA
2.7 V ≤ VIN ≤ 5.5 V
ILED = 500 µA
−2.5%
2.5%
–2%
1.7%
–8.5%
8.5%
VREG_CS
Regulated current sink
headroom voltage
Minimum current sink
headroom voltage for HVLED
current sinks
ILED = 95% of nominal, Full-scale current = 20.2 mA
VHR_MIN
ILED = 95% of nominal, Full-scale current =
20.2 mA , TA = 25°C
190
RDSON
NMOS switch on resistance
ISW = 500 mA, TA = 25°C
0.3
ICL_BOOST
NMOS switch current limit
VOVP
Output overvoltage protection
ƒSW
Switching frequency
DMAX
Maximum duty cycle
mA
Auto-headroom off, TA = 25°C
400
mV
275
880
TA = 25°C
mV
Ω
1120
1000
ON Threshold
OVP select bits = 11
2.7 V ≤ VIN ≤ 5.5 V
TA = 25°C
40
Hysteresis
TA = 25°C
1
Boost frequency select bit =
0
2.7 V ≤ VIN ≤ 5.5 V
Boost frequency select bit =
1
2.7 V ≤ VIN ≤ 5.5 V
38.75
41.1
450
TA = 25°C
V
550
500
900
TA = 25°C
mA
1100
kHz
1000
TA = 25°C
94%
HWEN INPUT
VHWEN_L
Logic low
2.7 V ≤ VIN ≤ 5.5 V
0
0.4
VHWEN_H
Logic high
2.7 V ≤ VIN ≤ 5.5 V
1.2
VIN
(1)
(2)
(3)
6
V
All voltages are with respect to the potential at the GND pin.
Minimum and Maximum limits are verified by design, test, or statistical analysis. Typical numbers are not verified, but do represent the
most likely norm. Unless otherwise specified, conditions for typical specifications are: VIN = 3.6 V and TA = 25°C.
LED current sink matching in the high-voltage current sinks (HVLED1 through HVLED3) is given as the maximum matching value
between any two current sinks, where the matching between any two high voltage current sinks (X and Y) is given as (IHVLEDX ( or
IHVLEDY) × IAVE(X-Y))/(IAVE(X-Y)) × 100. In this test all three HVLED current sinks are assigned to Bank A.
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Electrical Characteristics (continued)
Limits apply over the full operating ambient temperature range (−40°C ≤ TA ≤ 85°C) and VIN = 3.6 V, unless otherwise
specified.(1)(2)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
PWM INPUT
VPWM_L
Input logic low
2.7 V ≤ VIN ≤ 5.5 V
0
0.4
VPWM_H
Input logic high
2.7V ≤ VIN ≤ 5.5 V
1.31
VIN
tPWM
Minimum PWM input pulse
2.7 V ≤ VIN ≤ 5.5 V, PWM zero detect enabled
0.75
V
µs
2
I C-COMPATIBLE VOLTAGE SPECIFICATIONS (SCL, SDA)
VIL
Input logic low
2.7 V ≤ VIN ≤ 5.5 V
0
0.4
VIH
Input logic high
2.7 V ≤ VIN ≤ 5.5 V
1.29
VIN
VOL
Output logic low (SDA)
2.7 V ≤ VIN ≤ 5.5 V, ILOAD = 3 mA
400
V
mV
6.6 Timing Requirements
MIN
2
I C-COMPATIBLE TIMING SPECIFICATIONS (SCL, SDA)
NOM
MAX
UNIT
(1)
t1
SCL (clock period)
2.7 V ≤ VIN ≤ 5.5 V
2.5
µs
t2
Data In set-up time to SCL high
2.7 V ≤ VIN ≤ 5.5 V
100
ns
t3
Data out stable after SCL low
2.7 V ≤ VIN ≤ 5.5 V
0
ns
t4
SDA low set-up time to SCL low (start)
2.7 V ≤ VIN ≤ 5.5 V
100
ns
t5
SDA high hold time after SCL high (stop)
2.7 V ≤ VIN ≤ 5.5 V
100
ns
INTERNAL POR THRESHOLD AND HWEN TIMING SPECIFICATION
VIN ramp time = 100 µs
VPOR
tHWEN
(1)
POR reset release voltage threshold
1.7
2.1
VIN ramp time = 100 µs, TA =
25°C
2.7 V ≤ VIN ≤ 5.5 V, POR
reset complete
2
First I C start pulse after HWEN high
V
1.9
20
µs
POR reset complete, TA =
25°C
5.0
SCL and SDA must be glitch-free in order for proper brightness control to be realized.
t1
SCL
t5
t4
SDA_IN
t2
SDA_OUT
t3
2
Figure 1. I C-Compatible Interface Timing
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6.7 Typical Characteristics
2.5
0.5
2
IQ Shutdown (uA)
Rdson (Ohms)
0.45
0.4
0.35
0.3
0.2
-50
-25
0
25
50
75
100
1
0.5
VIN=2.7
VIN=3.6
VIN=5.5
0.25
1.5
VIN=5.5
VIN=3.6
VIN=2.7
0
-50
125
-25
0
Temperature (ƒC)
25
50
75
100
125
Temperature (ƒC)
C022
C024
Figure 2. RDSON vs Temperature
Figure 3. IQ Shutdown vs Temperature
2
250
POR Threshold (V)
HEADROOM VOLTAGE (mV)
300
200
150
100
1.5
1
0.5
VIN=2.7
VIN=3.6
VIN=5.5
50
0
-50
-25
0
25
50
75
100
0
-50
125
-25
0
Temperature (ƒC)
25
50
75
100
125
Temperature (ƒC)
C027
C023
Figure 5. POR Threshold vs Temperature
1.4
1.4
1.2
1.2
1
1
PWM VIL (V)
PWM VIH (V)
Figure 4. VHR_MIN vs Temperature
0.8
0.6
0.4
0.8
0.6
0.4
VIN=5.5
VIN=3.6
VIN=2.7
0.2
0
-50
-25
0
25
50
75
100
VIN=5.5
VIN=3.6
VIN=2.7
0.2
0
125
Temperature (ƒC)
-50
-25
0
25
50
75
100
C025
Figure 6. PWM VIH vs Temperature
8
125
Temperature (ƒC)
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C026
Figure 7. PWM VIL vs Temperature
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7 Detailed Description
7.1 Overview
The LM3697 provides the power for three high-voltage LED strings. The three high-voltage LED strings are
powered from an integrated boost converter. The device is configured over an I2C-compatible interface. The
LM3697 provides a Pulse Width Modulation (PWM) input for content adjustable brightness control.
7.1.1 PWM Input
The PWM input can be assigned to either of the high-voltage control banks. When assigned to a control bank,
the programmed current in the control bank becomes a function of the duty cycle (DPWM) at the PWM input and
the control bank brightness setting. When PWM is disabled, DPWM is equal to one.
7.1.2 HWEN Input
HWEN is the global hardware enable to the LM3697. HWEN must be pulled high to enable the device. HWEN is
a high-impedance input so it cannot be left floating. When HWEN is pulled low the LM3697 is placed in
shutdown, and all the registers are reset to their default state.
7.1.3 Thermal Shutdown
The LM3697 contains a thermal shutdown protection. In the event the die temperature reaches 140°C (typical),
the boost and current sink outputs shut down until the die temperature drops to typically 125°C (typical).
7.2 Functional Block Diagram
SW
IN
Selectable
Overvoltage
Protection
(16V, 24V, 32V, 40V)
SDA
I2C
Compatible Interface
1-A Current Limit
SCL
Boost
Converter
OVP
Selectable
500-kHz/1-MHz
Switching
Frequency
HWEN
Hardware Enable,
Reference, and
Thermal Shutdown
LED String Open/
Short Detection
PWM
Internal Low-Pass
Filter
High-Voltage Current
Sinks
HVLED1
Backlight LED Control
1. 5-bit Full Scale
Current Select
HVLED2
HVLED3
2. 11-bit brightness
adjustment
3. Linear/Exponential
Dimming
GND
4. LED Current
Ramping
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7.3 Feature Descriptions
7.3.1 High-Voltage LED Control
7.3.1.1 High-Voltage Boost Converter
The high-voltage boost converter provides power for the three high-voltage current sinks (HVLED1, HVLED2,
and HVLED3). The boost circuit operates using a 4.7-µH to 22-µH inductor and a 1-µF output capacitor. The
selectable 500-kHz or 1-MHz switching frequency allows for use of small external components and provides for
high boost-converter efficiency. HVLED1, HVLED2, and HVLED3 feature an adaptive current regulation scheme
where the feedback point (HVLED1, HVLED2, and HVLED3) regulates the LED headroom voltage VHR_MIN.
When there are different voltage requirements in the high-voltage LED strings (string mismatch), the LM3697
regulates the feedback point of the highest voltage string to VHR_MIN and drop the excess voltage of the lower
voltage string across the lower strings current sink.
7.3.1.2 High-Voltage Current Sinks (HVLED1, HVLED2 and HVLED3)
HVLED1, HVLED2, and HVLED3 control the current in the high-voltage LED strings as configured by Control
Bank A or B. Each Control Bank has 5-bit full-scale current programmability and 11-bit brightness control.
Assignment of the high-voltage current sinks to control bank is done through the HVLED Current Sink Output
Configuration register (see Table 5).
7.3.1.3 High-Voltage Current String Biasing
Each high-voltage current string can be powered from the LM3697’s boost output (COUT) or from an external
source. The feedback enable bits (HVLED Current Sink Feedback Enables register bits [2:0]) determine where
the high-voltage current string anodes connect. When set to '1' (default) the high-voltage current sink inputs are
included in the boost feedback loop. This allows the boost converter to adjust its output voltage in order to
maintain the LED headroom voltage VHR_MIN at the current sink input.
When powered from alternate sources the feedback enable bits must be set to '0'. This removes the particular
current sink from the boost feedback loop. In these configurations the application must ensure that the headroom
voltage across the high-voltage current sink is high enough to prevent the current sink from going into dropout
(see the Typical Characteristics for data on the high-voltage LED current vs VHR_MIN).
Setting the HVLED Current Sink Feedback Enables register bits also determines triggering of the shorted highvoltage LED String Fault flag (see the Fault Flags/Protection Features section).
7.3.2 Boost Switching-Frequency Select
The LM3697’s boost converter has two switching frequency settings. The switching frequency setting is
controlled via the Boost Frequency Select bit (bit 0 in the Boost Control register). Operating at the 500-kHz
switching frequency results in better efficiency under lighter load conditions due to the decreased switching
losses. In this mode the inductor must be between 10 µH and 22 µH. Operating at the 1-MHz switching
frequency results in better efficiency under higher load conditions resulting in lower conduction losses in the
MOSFETs and inductor. In this mode the inductor can be between 4.7 µH and 22 µH.
7.3.3 Automatic Switching Frequency Shift
The LM3697 has an automatic frequency select mode (bit 3 in the Boost Control register) to optimize the
frequency vs load dependent losses. In Auto-Frequency mode the boost converter switching frequency is
changed based on the high-voltage LED current. The threshold (Control A/B brightness code) at which the
frequency switchover occurs is configurable via the Auto-Frequency Threshold register. The Auto-Frequency
Threshold register contains an 8-bit code which is compared to the 8 MSB's of the brightness code. When the
brightness code is greater than the Auto-Frequency Threshold value the boost converter switching frequency is 1
MHz. When the brightness code is less than or equal to the Auto-Frequency Threshold register the boost
converter switching frequency is 500 kHz.
Figure 8 illustrates the LED efficiency improvement (3p5s LED configuration with a 4.7-µH inductor) when the
Auto-Frequency feature is enabled. When the LED brightness is less than or equal to 0x6C, the switching
frequency is 500 kHz, and it improves the LED efficiency by up to 6%. When the LED brightness is greater than
0x6C, the switching frequency is 1 MHz, and it improves LED efficiency by up to 2.2%.
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Feature Descriptions (continued)
1Mhz Eff - 500Khz Eff, 4.7uH, Three String
(Negative values when 500Khz more efficient)
3.0%
1Mhz LED Eff > 500Khz LED Eff
2.0%
¨()),&,(1&<
1.0%
0.0%
-1.0%
Auto-Frequency
Threshold = 0x6C
-2.0%
-3.0%
500Khz LED Eff > 1Mhz LED Eff
-4.0%
-5.0%
-6.0%
2048
1792
1536
1280
1024
768
512
256
0
BRIGHTNESS CODE
C002
Figure 8. Auto-Frequency Boost Efficiency Improvement Illustration
Table 1 summarizes the general recommendations for Auto-Frequency Threshold setting vs Inductance values
and LED string configurations. These are general recommendations — the optimum Auto-Frequency Threshold
setting must be evaluated for each application.
Table 1. Auto-Frequency Threshold Settings
THREE STRING
TWO STRING
INDUCTOR
AUTO-FREQUENCY
THRESHOLD
PEAK EFFICIENCY
IMPROVEMENT
PEAK
CONFIGURATION
AUTOFREQUENCY
THRESHOLD
4.7 µH
6C
2.2 %
3p5s
AC
1.1 %
2p6s
10 µH
74
1.7 %
3p4s
B4
1.3 %
2p5s
22 µH
7C
0.7 %
3p3s
BC
0.7 %
2p4s
PEAK EFFICIENCY
IMPROVEMENT
PEAK
CONFIGURATION
7.3.4 Brightness Register Current Control
The LM3697 features Brightness Register Current Control for simple user-adjustable current control set by
writing directly to the appropriate Control Bank Brightness Registers. The current for Control Banks A and B is a
function of the full-scale LED current, the 11-bit code in the respective brightness register, and the PWM input
duty cycle (if PWM is enabled). The Control A/B brightness must always be written with LSB's first and MSB's
last.
7.3.4.1 8-Bit Control (Preferred)
The preferred operating mode is to control the high-voltage LED brightness by setting the Control Bank LSB
register (3 LSB's) to zero and using only the Control Bank MSB register (8 MSB's). In this mode the LM3697
controls the 3 LSB's to ramp the high-voltage LED current using all 11-bits.
7.3.4.2 11-Bit Control
In this mode of operation, both Control Bank LSB and MSB registers must be written whenever a change in
Brightness is required. The high-voltage LED current will not change until the Control Bank MSB register is
written. If the brightness change affects only the 3 LSB's, the Control Bank MSB register (8 MSB's) must be rewritten to change the high-voltage LED current.
7.3.5 PWM Control
The LM3697's PWM input can be enabled for Control Banks A or B (see Table 14). Once enabled, the LED
current becomes a function of the code in the Control Bank Brightness Configuration Register and the PWM
input-duty cycle.
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The PWM input accepts a logic level voltage and internally filters it to an analog control voltage. This results in a
linear response of duty cycle to current, where 100% duty cycle corresponds to the programmed brightness code
multiplied by the Full-Scale Current setting.
Analog Domain
PWM Input
LPF
polarity
To Assigned
High Voltage
Current Sinks
Full-Scale
Current
Control
Digital Domain
Backlight Digital LED Control Block
DAC
Full-Scale Current Select
Brightness Setting
Exponential or Linear Mapping
Startup/Shutdown Ramp Generator
Runtime Ramp Generator
Figure 9. PWM Input Architecture
7.3.5.1 PWM Input Frequency Range
The usable input frequency range for the PWM input is governed on the low end by the cutoff frequency of the
internal low-pass filter (540 Hz, Q = 0.33) and on the high end by the propagation delays through the internal
logic. For frequencies below 2 kHz the current ripple begins to become a larger portion of the DC LED current.
Additionally, at lower PWM frequencies the boost output voltage ripple increases, causing a non-linear response
from the PWM duty cycle to the average LED current due to the response time of the boost. For the best
response of current vs. duty cycle, the PWM input frequency must be kept between 2 kHz and 100 kHz.
7.3.5.2 PWM Input Polarity
The PWM Input can be set for active low polarity, where the LED current is a function of the negative duty cycle.
This is set via the PWM Configuration register (see Table 14).
7.3.5.3 PWM Zero Detection
The LM3697 incorporates a feature to detect when the PWM input is near zero. After the near zero pulse width
has been detected the PWM pulse must be greater than tPWM to affect the HVLED output current (see Electrical
Characteristics ). Bit 3 in the PWM Configuration register is used to disable this feature.
7.3.6 Start-up/Shutdown Ramp
The high-voltage LED start-up and shutdown ramp times are independently configurable in the start-up/shutdown
transition time Register (see Table 6). There are 16 different start-up and 16 different shutdown times. The startup times can be programmed independently from the shutdown times, but each Control bank is not
independently configurable.
The start-up ramp time is from when the Control Bank is enabled to when the LED current reaches its initial set
point. The shutdown ramp time is from when the Control Bank is disabled to when the LED current reaches 0.
7.3.7 Run-Time Ramp
Current ramping from one brightness level to the next is programmed via the Control A and B Run-Time Ramp
Time Register (see Table 7). There are 16 different ramp-up times and 16 different ramp-down times. The rampup time can be programmed independently from the ramp-down time, but each Control Bank cannot be
independently programmed. For example, programming a ramp-up or ramp-down time is a global setting for all
high-voltage LED Control Banks.
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7.3.8 High-Voltage Control A and B Ramp Select
The LM3697 provides three options for Control A and B ramp times (see Table 8). When the Run-time Ramp
Select bits are set to 00, the control bank uses both the Start-up/Shutdown and Run-time ramp times. When the
Run-time Ramp Select bits are set to 01, the control bank uses the Start-up/Shutdown ramp times for both startup/shutdown and run-time. When the Run-time Ramp Select bits are set to 1x the control bank uses a zero µsec
run-time ramp.
7.4 Device Functional Modes
7.4.1 LED Current Mapping Modes
All control banks can be programmed for either exponential or linear mapping modes (see Figure 10 and
Figure 11). These modes determine the transfer characteristic of backlight code to LED current. Independent
mapping of Control Banks A and B is not allowed: both banks uses the same mapping mode.
7.4.1.1 Exponential Mapping
In Exponential Mapping Mode the current ramp (either up or down) appears to the human eye as a more uniform
transition then the linear ramp. This is due to the logarithmic response of the eye.
7.4.1.1.1 8-Bit Code Calculation
In Exponential Mapping Mode the brightness code to backlight current transfer function is given by the equation:
ILED = ILED_FULLSCALE x 0.85
(44 -
Code + 1
5.8181818
)
x DPWM
(1)
Where ILED_FULLSCALE is the full-scale LED current setting (see Table 10), Code is the 8-bit backlight code in the
Control Brightness MSB register and DPWM is the PWM Duty Cycle.
7.4.1.1.2 11-Bit Code Calculation
In Exponential Mapping Mode the brightness code to backlight current transfer function is given by the equation:
ILED = ILED_FULLSCALE x 0.85
Code
+1
8
(44 - 5.8181818
)
x DPWM
(2)
Where ILED_FULLSCALE is the full-scale LED current setting (see Table 10), Code is the 11-bit backlight code in the
Control Brightness MSB and LSB registers and DPWM is the PWM Duty Cycle.
7.4.1.2 Linear Mapping
In Linear Mapping Mode the brightness code to backlight current has a linear relationship.
7.4.1.2.1 8-Bit Code Calculation
The 8-bit linear mapping follows the equation:
ILED = ILED_FULLSCALE x
1 x Code x D
PWM
255
(3)
Where ILED_FULLSCALE is the full-scale LED current setting, Code is the 8-bit backlight code in the Control
Brightness MSB register and DPWM is the PWM Duty Cycle.
7.4.1.2.2 11-Bit Code Calculation
The 11-bit linear mapping follows the equation:
ILED = ILED_FULLSCALE x
1 x Code x D
PWM
2047
(4)
Where ILED_FULLSCALE is the full-scale LED current setting, Code is the 11-bit backlight code in the Control
Brightness MSB and LSB registers and DPWM is the PWM Duty Cycle.
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Device Functional Modes (continued)
21.00
21
Exponential
Linear
18.00
15
LED CURRENT (mA)
15.00
LED CURRENT (mA)
Exponential
Linear
18
12.00
9.00
6.00
12
9
6
3.00
3
0.00
0
2048
1792
1536
1280
1024
768
512
BRIGHTNESS CODE
C001
Figure 10. LED Current Mapping Modes (8-Bit)
256
0
256
224
192
160
128
96
64
32
0
BRIGHTNESS CODE
C001
Figure 11. LED Current Mapping Modes (11-Bit)
7.4.2 Fault Flags/Protection Features
The LM3697 contains both LED-open and LED-short fault detection. These fault detections are designed to be
used in production level testing and not normal operation. For the fault flags to operate, they must be enabled via
the LED Fault Enable Register (see Table 22). The following sections detail the proper procedure for reading
back open and short faults in the high-voltage LED strings.
7.4.2.1 Open LED String (HVLED)
An open LED string is detected when the voltage at the input to any active high-voltage current sink has fallen
below 200 mV, and the boost output voltage has hit the OVP threshold. This test assumes that the HVLED string
that is being detected for an open is connected to the LM3697 device's boost output (COUT+) (see Table 20).
For an HVLED string not connected to the LM3697's boost output voltage, but connected to another voltage
source, the boost output will not trigger the OVP flag. In this case an open LED string is not detected.
The procedure for detecting an open fault in the HVLED current sinks (provided they are connected to the boost
output voltage) is:
• Apply power to the LM3697
• Enable Open Fault (Register 0xB4, bit [0] = 1)
• Assign HVLED1, HVLED2 and HVLED3 to Bank A (Register 0x10, Bits [2:0] = (0, 0, 0)
• Set the start-up ramp times to the fastest setting (Register 0x11 = 0x00)
• Set Bank A full-scale current to 20.2 mA (Register 0x17 = 0x13)
• Configure HVLED1, HVLED2 and HVLED3 for LED string anode connected to COUT (Register 0x19, bits[2:0]
= (1,1,1))
• Set Control A Brightness MSB to max (Register 0x21 = 0xFF)
• Enable Bank A (Register 0x24 Bit[0] = 1
• Wait 4 ms
• Read back bits[2:0] of register 0xB0. Bit [0] = 1 (HVLED1 open). Bit [1] = 1 (HVLED2 open). Bit [2] = 1
(HVLED3 open)
• Disable all banks (Register 0x24 = 0x00)
7.4.2.2 Shorted LED String (HVLED)
The LM3697 features an LED short fault flag indicating one or more of the HVLED strings have experienced a
short. The method for detecting a shorted HVLED strings is if the current sink is enabled and the string voltage
(VOUT - VHVLED1/2/3) falls to below (VIN - 1 V) . This test must be performed on one HVLED string at a time.
Performing the test with more than one current sink enabled can result in a faulty reading.
The procedure for detecting a short in an HVLED string is:
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Device Functional Modes (continued)
•
•
•
•
•
•
•
•
•
•
•
•
Apply power to the LM3697
Enable Short Fault (Register 0xB4, bit [1] = 1)
Assign HVLED1 to Bank A (Register 0x10, Bits [2:0] = (1, 1, 0)
Set the startup ramp times to the fastest setting (Register 0x11 = 0x00)
Set Bank A full-scale current to 20.2 mA (Register 0x17 = 0x13)
Enable Feedback on the HVLED Current Sinks (Register 0x19, bits[2:0] = (1,1,1))
Set Control A Brightness MSB to max (Register 0x21 = 0xFF)
Enable Bank A (Register 0x24 Bit[0] = 1)
Wait 4 ms
Read back bits[0] of register 0xB2. 1 = HVLED1 short.
Disable all banks (Register 0x24 = 0x00)
Repeat the procedure for the HVLED2 and HVLED3 strings
7.4.2.3 Overvoltage Protection (Inductive Boost)
The overvoltage protection threshold (OVP) on the LM3697 has 4 different configurable options (16 V, 24 V, 32
V, and 40 V). The OVP protects the device and associated circuitry from high voltages in the event the highvoltage LED string becomes open. During normal operation, the LM3697 device’s inductive boost converter
boosts the output up so as to maintain VHR at the active, high-voltage (COUT connected) current sink inputs.
When a high-voltage LED string becomes open, the feedback mechanism is broken, and the boost converter
over-boosts the output. When the output voltage reaches the OVP threshold the boost converter stops switching,
thus allowing the output node to discharge. When the output discharges to VOVP minus 1 V the boost converter
begins switching again. The OVP sense is at the OVP pin, so this pin must be connected directly to the inductive
boost output capacitor’s positive terminal.
For high-voltage current sinks that have the HVLED Current Sink Feedback Enable setting such that the highvoltage current sinks anodes are not connected to COUT (feedback is disabled), the overvoltage sense
mechanism is not in place to protect the input to the high-voltage current sink. In this situation the application
must ensure that the voltage at HVLED1, HVLED2 or HVLED3 doesn’t exceed 40 V.
The default setting for OVP is set at 16 V. For applications that require higher than 16 V at the boost output, the
OVP threshold must be programmed to a higher level after power up.
7.4.2.4 Current Limit (Inductive Boost)
The NMOS switch current limit for the LM3697 device’s inductive boost is set at 1 A (typical). When the current
through the LM3697’s NFET switch hits this overcurrent protection threshold (OCP), the device turns the NFET
off, and the inductor’s energy is discharged into the output capacitor. Switching is then resumed at the next
cycle. The current limit protection circuitry can operate continuously each switching cycle. The result is that
during high-output power conditions the device can continuously run in current limit. Under these conditions the
LM3697’s inductive boost converter stops regulating the headroom voltage across the high-voltage current sinks.
This results in a drop in the LED current.
7.4.3 I2C-Compatible Interface
7.4.3.1 Start And Stop Conditions
The LM3697 is controlled via an I2C-compatible interface. START and STOP conditions classify the beginning
and the end of the I2C session. A START condition is defined as SDA transitioning from HIGH to LOW while SCL
is HIGH. A STOP condition is defined as SDA transitioning from LOW to HIGH while SCL is HIGH. The I2C
master always generates START and STOP conditions. The I2C bus is considered busy after a START condition
and free after a STOP condition. During data transmission the I2C master can generate repeated START
conditions. A START and a repeated START condition are equivalent function-wise. The data on SDA must be
stable during the HIGH period of the clock signal (SCL). In other words, the state of SDA can only be changed
when SCL is LOW.
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Device Functional Modes (continued)
SDA
SCL
S
P
Start Condition
Stop Condition
Figure 12. Start And Stop Sequences
7.4.3.2 I2C-Compatible Address
The chip address for the LM3697 is 0110110 (36h). After the START condition, the I2C master sends the 7-bit
chip address followed by an eighth read or write bit (R/W). R/W= 0 indicates a WRITE and R/W = 1 indicates a
READ. The second byte following the chip address selects the register address to which the data is written. The
third byte contains the data for the selected register.
7.4.3.3 Transferring Data
Every byte on the SDA line must be eight bits long, with the most significant bit (MSB) transferred first. Each byte
of data must be followed by an acknowledge bit (ACK). The acknowledge related clock pulse (9th clock pulse) is
generated by the master. The master releases SDA (HIGH) during the 9th clock pulse. The LM3697 pulls down
SDA during the 9th clock pulse signifying an acknowledge. An acknowledge is generated after each byte has
been received.
Table 2 lists the available registers within the LM3697.
7.4.3.4 High-Speed Mode
The LM3697 supports only Standard and Fast mode I2C operation. High Speed mode is not supported. If the
LM3697 is connected to a I2C-bus with a HS-mode device a dummy I2C cycle is required after the HS-mode
command is complete. The dummy cycle can be a read or write to any I2C slave address.
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7.5 Register Maps
Table 2. LM3697 Register Descriptions
ADDRESS
POWER-ON RESET
OPERATION
Revision
NAME
0x00
0x00
Dynamic
Software Reset
0x01
0x00
Dynamic
HVLED Current Sink Output Configuration
0x10
0x06
Static
Control A Start-up/Shutdown Ramp Time
0x11
0x00
Static
Control B Start-up/Shutdown Ramp Time
0x12
0x00
Static
Control A/B Run time Ramp Time
0x13
0x00
Static
Control A/B Run time Ramp Configuration
0x14
0x00
Static
Reserved
0x15
0x33
Static
Brightness Configuration
0x16
0x00
Static
Control A Full-Scale Current Setting
0x17
0x13
Static
Control B Full-Scale Current Setting
0x18
0x13
Static
HVLED Current Sink Feedback Enables
0x19
0x07
Static
Boost Control
0x1A
0x00
Static
Auto-Frequency Threshold
0x1B
0xCF
Static
PWM Configuration
0x1C
0x0C
Dynamic (1)
Control A Brightness LSB
0x20
0x00
Dynamic (2)
Control A Brightness MSB
0x21
0x00
Dynamic
Control B Brightness LSB
0x22
0x00
Dynamic (2)
Control B Brightness MSB
0x23
0x00
Dynamic
Control Bank Enables
0x24
0x00
Dynamic
HVLED Open Faults
0xB0
0x00
Production Test Only
HVLED Short Faults
0xB2
0x00
Production Test Only
LED Fault Enables
0xB4
0x00
Production Test Only
(1)
(2)
The PWM inputmust always be in the inactive state when setting the Control bank PWM Enable bit. The PWM configuration bits must
only be changed when the PWM is disabled for both Control Banks.
The Control Brightness MSB Register must be written for the Control Brightness LSB Register value to take effect.
Table 3. Revision (Address 0x00)
Bits [7:4]
Not Used
Bits [3:0]
Silicon Revision
Reserved
0000 = Rev. A Silicon
Table 4. Software Reset (Address 0x01)
Bits [7:1]
Not Used
Bit [0]
Silicon Revision
0 = Normal Operation
1 = Software Reset (self-clearing)
Reserved
Table 5. HVLED Current Sink Output Configuration (Address 0x10)
Bits [7:3]
Not Used
Reserved
Bit [2]
HVLED3 Configuration
0 = Control A
1 = Control B (default)
Bit [1]
HVLED2 Configuration
0 = Control A
1 = Control B (default)
Bit [0]
HVLED1 Configuration
0 = Control A (default)
1 = Control B
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Table 6. Control A and B Start-up/Shutdown Ramp Time (Address 0x11 and 0x12)
Bits [7:4]
Start-up Ramp
Bits [3:0]
Shutdown Ramp
0000 = 2048 µs (default)
0001 = 262 ms
0010 = 524 ms
0011 = 1.049 s
0100 = 2.09 s
0101 = 4.194 s
0110 = 8.389 s
0111 = 16.78 s
1000 = 33.55 s
1001 = 41.94 s
1010 = 50.33 s
1011 = 58.72 s
1100 = 67.11 s
1101 = 83.88 s
1110 = 100.66 s
1111 = 117.44 s
0000 = 2048 µs (default)
0001 = 262 ms
0010 = 524 ms
0011 = 1.049 s
0100 = 2.097 s
0101 = 4.194 s
0110 = 8.389 s
0111 = 16.78 s
1000 = 33.55 s
1001 = 41.94 s
1010 = 50.33 s
1011 = 58.72 s
1100 = 67.11 s
1101 = 83.88 s
1110 = 100.66 s
1111 = 117.44 s
Table 7. Control A and B Run-Time Ramp Time (Address 0x13)
Bits [7:4]
Transition Time Ramp Up
000 = 2048 µs (default)
001 = 262 ms
010 = 524 ms
011 = 1.049 s
100 = 2.097 s
101 = 4.194 s
110 = 8.389 s
111 = 16.78 s
1000 = 33.55 s
1001 = 41.94 s
1010 = 50.33 s
1011 = 58.72 s
1100 = 67.11 s
1101 = 83.88 s
1110 = 100.66 s
1111 = 117.44 s
Bits [3:0]
Transition Time Ramp Down
000 = 2048 µs (default)
001 = 262 ms
010 = 524 ms
011 = 1.049 s
100 = 2.097 s
101 = 4.194 s
110 = 8.389 s
111 = 16.78 s
1000 = 33.55 s
1001 = 41.94 s
1010 = 50.33 s
1011 = 58.72 s
1100 = 67.11 s
1101 = 83.88 s
1110 = 100.66 s
1111 = 117.44 s
Table 8. Control A and B Run-Time Ramp Configuration (Address 0x14)
Bits [7:4]
Not Used
Reserved
Bits [3:2]
Control B Run-time Ramp Select
Bits [1:0]
Control A Run-time Ramp Select
00 = Control A/B Runtime Ramp Times
(default)
01 = Control B Start-up/Shutdown Ramp
Times
1x = 0 µs Ramp Time
00 = Control A/B Runtime Ramp Times
(default)
01 = Control A Start-up/Shutdown Ramp
Times
1x = 0 µs Ramp Time
Table 9. Control A and B Brightness Configuration (Address 0x16)
Bits [7:4]
Not Used
Reserved
18
Bit [3]
Bit [2]
Control B Dither Disable Control A Dither Disable
0 Enable (default)
1 Disable
0 Enable (default)
1 Disable
Bit [1]
Not Used
Reserved
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Bit [0]
Control A/B Mapping
Mode
0 Exponential (default)
1 Linear
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Table 10. Control A and B Full-Scale Current Setting (Address 0x17 and 0x18)
Bits [7:5]
Not Used
Bits [4:0]
Control A, B Full-Scale Current Select Bits
Reserved
00000 = 5 mA
10011 = 20.2 mA (default)
11111 = 29.8 mA
(0.8 mA steps, FS = 5 + code * 0.8 mA)
Table 11. HVLED Current Sink Feedback Enables (Address 0x19)
Bits [7:3]
Not Used
Reserved
Bit [2]
HVLED3 Feedback Enable
Bit [1]
HVLED2 Feedback Enable
Bit [0]
HVLED1 Feedback Enable
0 = LED anode is NOT CONNECTED
to COUT
1 = LED anode is CONNECTED to
COUT (default)
0 = LED anode is NOT CONNECTED
to COUT
1 = LED anode is CONNECTED to
COUT (default)
0 = LED anode is NOT CONNECTED
to COUT
1 = LED anode is CONNECTED to
COUT (default)
Table 12. Boost Control (Address 0x1A)
Bits [7:5]
Not Used
Reserved
Bit [4]
Auto-Headroom Enable
0 = Disable (default)
1 = Enable
Bit [3]
Auto-Frequency Enable
0 = Disable (default)
1 = Enable
Bits [2:1]
Boost OVP Select
00
01
10
11
= 16
= 24
= 32
= 40
V (default)
V
V
V
Bit [0]
Boost Frequency Select
0 = 500 kHz (default)
1 = 1 MHz
Table 13. Auto-Frequency Threshold (Address 0x1B)
Bits [7:0]
Auto-Frequency Threshold (default = 11001111)
Table 14. PWM Configuration (Address 0x1C)
Bits [7:4]
Not Used
Reserved
Bit [3]
PWM Zero Detection
Enable
0 = Disable
1 = Enable (default)
Bit [2]
PWM Polarity
0 = Active Low
1 = Active High (default)
Bit [1]
Control B PWM Enable
0 = Disable (default)
1 = Enable
Bit [0]
Control A PWM Enable
0 = Disable (default)
1 = Enable
Table 15. Control A Brightness LSB (Address 0x20)
Bits [7:3]
Not Used
Reserved
Bits [2:0]
Control A Brightness [2:0]
Brightness LSB
Table 16. Control A Brightness MSB (Address 0x21)
Bits [7:0]
Control A Brightness [11:3]
Brightness MSB
(LED current ramping does not start until the MSB is written, LSB must always be written before MSB)
Table 17. Control B Brightness LSB (Address 0x22)
Bits [7:3]
Not Used
Reserved
Bits [2:0]
Control B Brightness [2:0]
Brightness LSB
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Table 18. Control B Brightness MSB (Address 0x23)
Bits [7:0]
Control B Brightness [11:3]
Brightness MSB
(LED current ramping does not start until the MSB is written, LSB must always be written before MSB)
Table 19. Control Bank Enables (Address 0x24)
Bit [1]
Control B
Enable
Bit [7:2]
Not Used
Reserved
0 = Disable
(default)
1 = Enable
Bit [0]
Control A
Enable
0 = Disable
(default)
1 = Enable
Table 20. HVLED Open Faults (Address 0xB0)
Bits [7:3]
Not Used
Bit [2]
HVLED3 Open
Bit [1]
HVLED2 Open
Bit [0]
HVLED1 Open
Reserved
0 = Normal Operation
1 = Open
0 = Normal Operation
1 = Open
0 = Normal Operation
1 = Open
Table 21. HVLED Short Faults (Address 0xB2)
Bits [7:3]
Not Used
Bit [2]
HVLED3 Short
Bit [1]
HVLED2 Short
Bit [0]
HVLED1 Short
Reserved
0 = Normal Operation
1 = Short
0 = Normal Operation
1 = Short
0 = Normal Operation
1 = Short
Table 22. LED Fault Enable (Address 0xB4)
Bits [7:2]
Not Used
Bit [1]
Short Faults Enable
Bit [0]
Open Faults Enable
Reserved
0 = Disable (default)
1 = Enable
0 = Disable (default)
1 = Enable
20
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8 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
The LM3697 provides a complete high-performance LED lighting solution for mobile handsets. The LM3697 is
highly configurable and can support the LED configurations summarized in Table 23. The LM3697 provides
internal ramp time generators to provide smooth LED dimming with 11-bit control while requiring only 8-bit control
from the host controller. The LM3697EVM is available with GUI software to aid understanding of the LM3697
operation.
Table 23. Supported LED Configurations
NUMBER OF LED STRINGS
MAXIMUM NUMBER OF SERIES LEDS
3
7
2
10
1
10
8.2 Typical Applications
Figure 13. LM3697 Schematic
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Typical Applications (continued)
8.2.1 Design Requirements
For typical LM3697 white LED applications, use the parameters listed in Table 24.
Table 24. Design Parameters
DESIGN PARAMETER
EXAMPLE VALUE
Full-scale current setting
0.0202 A
Minimum Input Voltage
3V
LED series/parallel configuration
7s3p
LED maximum forward voltage (Vf)
3.5 V
Efficiency
80%
The designer needs to know the following:
• Full-scale current setting
• Minimum input voltage
• LED series/parallel configuration
• LED maximum Vf voltage
• LM3697 Efficiency for LED configuration
The full-scale current setting, number of led strings, number of series LEDs, and minimum input voltage are
needed in order to calculate the peak input current. This information guides the designer to make the appropriate
inductor selection for the application.
The LM3697 Boost converter output voltage (VOUT) is calculated as follows: # series LEDs × Vƒ + 0.4 V.
The LM3697 Boost converter output current (IOUT) is calculated as follows: # parallel LED strings × full-scale
current.
The LM3697 peak input current (IIN_PK) is calculated as follows:
IIN_PK ! VOUT u IOUT y Minimum VIN y Efficiency
VOUT
24.9 V
IOUT
0.0606 A
7 u 3.5 V 0.4 V
IIN_PK ! 0.629 A
0.0202 u 3
24.9 V u 0.0606 A y 3 V y 0.8
8.2.2 Detailed Design Procedure
8.2.2.1 Boost Converter Maximum Output Power
The LM3697 devices maximum output power is governed by two factors: the peak current limit (ICL = 880 mA
min.), and the maximum output voltage (VOUT). When the application causes either of these limits to be reached
it is possible that the proper current regulation and matching between LED current strings will not be met.
8.2.2.1.1 Peak Current Limited
In the case of a peak current limited situation, when the peak of the inductor current hits the LM3697 device's
current limit, the NFET switch turns off for the remainder of the switching period. If this happens each switching
cycle the LM3697 regulates the peak of the inductor current instead of the headroom across the current sinks.
This can result in the dropout of the boost output connected current sinks, and the LED current dropping below
its programmed level.
The peak current in a boost converter is dependent on the value of the inductor, total LED current in the boost
(IOUT), the boost output voltage (VOUT) (which is the highest voltage LED string + VHR ), the input voltage (VIN),
the switching frequency (ƒSW), and the efficiency (Output Power/Input Power). Additionally, the peak current is
different depending on whether the inductor current is continuous during the entire switching period (CCM), or
discontinuous (DCM) where it goes to 0 before the switching period ends. For CCM the peak inductor current is
given by:
22
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IPEAK =
IOUT x VOUT
+
VIN x efficiency
VIN
2 x ¦SW x L
x 1-
VIN x efficiency
VOUT
(5)
For DCM the peak inductor current is given by:
2 u IOUT
IPEAK =
´
¶ SW
u L u efficiency
u §VOUT - VIN u efficiency·
©
¹
(6)
To determine which mode the circuit is operating in (CCM or DCM) it is necessary to perform a calculation to test
whether the inductor current ripple is less than the anticipated input current (IIN). If ΔIL is less than IIN then the
device is operating in CCM. If ΔIL is greater than IIN then the device is operating in DCM.
IOUT u VOUT
VIN u efficiency
>
VIN
´
¶SW
uL
u §1
©
VIN u efficiency ·
VOUT
¹
(7)
Typically at currents high enough to reach the LM3697's peak current limit, the device is operating in CCM.
0.100
0.095
0.090
0.085
0.080
0.075
0.070
0.065
0.060
0.055
0.050
0.045
0.040
0.035
IOUT (A)
IOUT (A)
Figure 14 and Figure 15 show the output current and voltage derating for a 10-µH and a 22-µH inductor. These
plots take Equation 5 and Equation 6 and plot VOUT and IOUT with varying VIN, a constant peak current of 880 mA
(ICL_MIN), 500-kHz switching frequency, and a constant efficiency of 85%. Using these curves can give a good
design guideline on selecting the correct inductor for a given output power requirement. A 10-µH inductor will
typically be a smaller device with lower on resistance, but the peak currents is higher. A 22-µH inductor provides
for lower peak currents but a larger sized device is required to match the DC resistance of a 10-µH inductor.
22
24
26
30
34
38
22
24
26
30
34
38
5.5
5.3
5.1
4.9
4.7
4.5
4.3
4.1
3.9
3.7
3.5
3.3
3.1
2.9
2.7
5.5
5.3
5.1
4.9
4.7
4.5
4.3
4.1
3.9
3.7
3.5
3.3
3.1
2.9
2.7
VIN (V)
0.100
0.095
0.090
0.085
0.080
0.075
0.070
0.065
0.060
0.055
0.050
0.045
0.040
0.035
C052
Figure 14. Maximum Output Power (22 µH)
VIN (V)
C001
Figure 15. Maximum Output Power (10 µH)
8.2.2.1.2 Output Voltage Limited
In the case of an output voltage limited situation (VOUT = VOVP), when the boost output voltage hits the LM3697
device's OVP threshold, the NFET turns off and stays off until the output voltage falls below the hysteresis level
(typically 1 V below the OVP threshold). This results in the boost converter regulating the output voltage to the
programmed OVP threshold (16 V, 24 V, 32 V, or 40 V), causing the current sinks to go into dropout. The default
OVP threshold is set at 16 V. For LED strings higher than typically 4 series LEDs, the OVP has to be
programmed higher after power-up, Software Reset, or HWEN reset.
8.2.2.2 Inductor Selection
The boost circuit operates using a 4.7-µH to 22-µH inductor. The inductor selected must have a saturation
current greater than the peak operating current.
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8.2.2.3 Output Capacitor Selection
The LM3697's inductive boost converter requires a 1-µF (X5R or X7R) ceramic capacitor to filter the output
voltage. The voltage rating of the capacitor depends on the selected OVP setting. For the 16 V setting a 16-V
capacitor must be used. For the 24-V setting a 25-V capacitor must be used. For the 32-V setting, a 35-V
capacitor must be used. For the 40-V setting a 50-V capacitor must be used. Pay careful attention to the
capacitor's tolerance and DC bias response. For proper operation the degradation in capacitance due to
tolerance, DC bias, and temperature, must stay above 0.4 µF. This might require placing two devices in parallel
in order to maintain the required output capacitance over the device operating range, and series LED
configuration.
8.2.2.4 Schottky Diode Selection
The Schottky diode must have a reverse breakdown voltage greater than the LM3697 device’s maximum output
voltage (see Overvoltage Protection (Inductive Boost) section). Additionally, the diode must have an average
current rating high enough to handle the LM3697’s maximum output current, and at the same time the diode's
peak current rating must be high enough to handle the peak inductor current. Schottky diodes are required due
to their lower forward voltage drop (0.3 V to 0.5 V) and their fast recovery time.
8.2.2.5 Input Capacitor Selection
The LM3697 device's inductive boost converter requires a 2.2-μF (X5R or X7R) ceramic capacitor to filter the
input voltage. The input capacitor filters the inductor current ripple and the internal MOSFET driver currents
during turn on of the internal power switch.
8.2.2.6 Application Circuit Component List
COMPONENT
MANUFACTURER
VALUE
PART NUMBER
SIZE (mm)
CURRENT/VOLTAGE RATING
(RESISTANCE)
L
TDK
10 µH
VLF302512MT-100M
2.5 x 3.0 x 1.2
620 mA/0.25 Ω
COUT
TDK
1.0 µF
C2012X5R1H105
0805
50 V
CIN
TDK
2.2 µF
C1005X5R1A225
0402
10 V
Diode
On-Semi
Schottky
NSR0240V2T1G
SOD-523
40 V, 250 mA
8.2.3 Application Performance Plots
VIN = 3.6 V, full-scale current = 20.2 mA, LEDs are WLEDs part # SML-312WBCW(A), Typical Application Circuit , TA = 25°C
unless otherwise specified. Efficiency is VOUT × (IHVLED1 + IHVLED2 + IHVLED3)/(VIN × IIN), matching curves are (ΔILED_MAX/ILED_AVE).
Three String, L=22µH, 500kHz
Three String, L=22µH, 1MHz
92%
90%
90%
88%
88%
86%
86%
EFFICIENCY (%)
EFFICIENCY (%)
92%
84%
82%
80%
78%
76%
84%
82%
80%
78%
76%
74%
74%
72%
72%
70%
70%
2.5
3
3.5
4
4.5
5
5.5
2.5
VIN (V)
3
3.5
4
4.5
5
C002
Top to Bottom: 3x3, 3x4, 3x5, 3x6, 3x7 (LEDs)
C002
Top to Bottom: 3x3, 3x4, 3x5, 3x6, 3x7 (LEDs)
Figure 16. Boost Efficiency vs VIN
24
5.5
VIN (V)
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Figure 17. Boost Efficiency vs VIN
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VIN = 3.6 V, full-scale current = 20.2 mA, LEDs are WLEDs part # SML-312WBCW(A), Typical Application Circuit , TA = 25°C
unless otherwise specified. Efficiency is VOUT × (IHVLED1 + IHVLED2 + IHVLED3)/(VIN × IIN), matching curves are (ΔILED_MAX/ILED_AVE).
Two String, L=22µH, 500kHz
Two String, L=22µH, 1MHz
92%
90%
90%
88%
88%
86%
86%
EFFICIENCY (%)
EFFICIENCY (%)
92%
84%
82%
80%
78%
76%
84%
82%
80%
78%
76%
74%
74%
72%
72%
70%
70%
2.5
3
3.5
4
4.5
5
5.5
2.5
3
3.5
VIN (V)
4
4.5
5
5.5
VIN (V)
C002
Top to Bottom: 2x3, 2x4, 2x5, 2x6, 2x7, 2x8, 2x9, 2x10 (LEDs)
C002
Top to Bottom: 2x3, 2x4, 2x5, 2x6, 2x7, 2x8, 2x9, 2x10 (LEDs)
Figure 18. Boost Efficiency vs VIN
One String, L=22µH, 500kHz
92%
One String, L=22µH, 1MHz
92%
90%
90%
88%
88%
86%
86%
EFFICIENCY (%)
EFFICIENCY (%)
Figure 19. Boost Efficiency vs VIN
84%
82%
80%
78%
76%
84%
82%
80%
78%
76%
74%
74%
72%
72%
70%
70%
2.5
3
3.5
4
4.5
5
5.5
2.5
3
3.5
VIN (V)
4
4.5
5
5.5
VIN (V)
C002
Top to Bottom: 1x3, 1x4, 1x5, 1x6, 1x7, 1x8, 1x9, 1x10 (LEDs)
C002
Top to Bottom: 1x3, 1x4, 1x5, 1x6, 1x7, 1x8, 1x9, 1x10 (LEDs)
Figure 20. Boost Efficiency vs VIN
Three String, L=10µH, 500kHz
90%
Three String, L=10µH, 1MHz
90%
88%
88%
86%
86%
84%
84%
EFFICIENCY (%)
EFFICIENCY (%)
Figure 21. Boost Efficiency vs VIN
82%
80%
78%
76%
82%
80%
78%
76%
74%
74%
72%
72%
70%
70%
2.5
3
3.5
4
4.5
5
5.5
2.5
VIN (V)
3
3.5
4
4.5
5
5.5
VIN (V)
C002
Top to Bottom: 3x3, 3x4, 3x5, 3x6, 3x7 (LEDs)
C002
Top to Bottom: 3x3, 3x4, 3x5, 3x6, 3x7 (LEDs)
Figure 22. Boost Efficiency vs VIN
Figure 23. Boost Efficiency vs VIN
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VIN = 3.6 V, full-scale current = 20.2 mA, LEDs are WLEDs part # SML-312WBCW(A), Typical Application Circuit , TA = 25°C
unless otherwise specified. Efficiency is VOUT × (IHVLED1 + IHVLED2 + IHVLED3)/(VIN × IIN), matching curves are (ΔILED_MAX/ILED_AVE).
Two String, L=10µH, 500kHz
Two String, L=10µH, 1MHz
90%
88%
88%
86%
86%
84%
84%
EFFICIENCY (%)
EFFICIENCY (%)
90%
82%
80%
78%
76%
82%
80%
78%
76%
74%
74%
72%
72%
70%
70%
2.5
3
3.5
4
4.5
5
5.5
2.5
3
3.5
VIN (V)
4
4.5
5
5.5
VIN (V)
C002
Top to Bottom: 2x3, 2x4, 2x5, 2x6, 2x7, 2x8, 2x9, 2x10 (LEDs)
C002
Top to Bottom: 2x3, 2x4, 2x5, 2x6, 2x7, 2x8, 2x9, 2x10 (LEDs)
Figure 24. Boost Efficiency vs VIN
One String, L=10µH, 500kHz
92%
One String, L=10µH, 1MHz
92%
90%
90%
88%
88%
86%
86%
EFFICIENCY (%)
EFFICIENCY (%)
Figure 25. Boost Efficiency V vs VIN
84%
82%
80%
78%
76%
84%
82%
80%
78%
76%
74%
74%
72%
72%
70%
70%
2.5
3
3.5
4
4.5
5
5.5
2.5
3
3.5
VIN (V)
4
4.5
5
5.5
VIN (V)
C002
Top to Bottom: 1x3, 1x4, 1x5, 1x6, 1x7, 1x8, 1x9, 1x10 (LEDs)
C002
Top to Bottom: 1x3, 1x4, 1x5, 1x6, 1x7, 1x8, 1x9, 1x10 (LEDs)
Figure 26. Boost Efficiency vs VIN
Three String, L=4.7µH, 500kHz
90%
Three String, L=4.7µH, 1MHz
90%
88%
88%
86%
86%
84%
84%
EFFICIENCY (%)
EFFICIENCY (%)
Figure 27. Boost Efficiency vs VIN
82%
80%
78%
76%
82%
80%
78%
76%
74%
74%
72%
72%
70%
70%
2.5
3
3.5
4
4.5
5
5.5
2.5
VIN (V)
3
3.5
4
4.5
5
C002
Top to Bottom: 3x3, 3x4, 3x5, 3x6, 3x7 (LEDs)
C002
Top to Bottom: 3x3, 3x4, 3x5, 3x6, 3x7 (LEDs)
Figure 28. Boost Efficiency vs VIN
26
5.5
VIN (V)
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Figure 29. Boost Efficiency vs VIN
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VIN = 3.6 V, full-scale current = 20.2 mA, LEDs are WLEDs part # SML-312WBCW(A), Typical Application Circuit , TA = 25°C
unless otherwise specified. Efficiency is VOUT × (IHVLED1 + IHVLED2 + IHVLED3)/(VIN × IIN), matching curves are (ΔILED_MAX/ILED_AVE).
Two String, L=4.7µH, 500kHz
Two String, L=4.7µH, 1MHz
88%
86%
86%
84%
84%
EFFICIENCY (%)
EFFICIENCY (%)
88%
82%
80%
78%
76%
82%
80%
78%
76%
74%
74%
72%
72%
70%
70%
2.5
3
3.5
4
4.5
5
5.5
2.5
3
3.5
VIN (V)
4
4.5
5
5.5
VIN (V)
C002
Top to Bottom: 2x3, 2x4, 2x5, 2x6, 2x7, 2x8, 2x9, 2x10 (LEDs)
C002
Top to Bottom: 2x3, 2x4, 2x5, 2x6, 2x7, 2x8, 2x9, 2x10 (LEDs)
Figure 30. Boost Efficiency vs VIN
One String, L=4.7µH, 500kHz
88%
One String, L=4.7µH, 1MHz
88%
86%
86%
84%
84%
EFFICIENCY (%)
EFFICIENCY (%)
Figure 31. Boost Efficiency vs VIN
82%
80%
78%
76%
82%
80%
78%
76%
74%
74%
72%
72%
70%
70%
2.5
3
3.5
4
4.5
5
5.5
2.5
3
VIN (V)
3.5
4
4.5
5
5.5
VIN (V)
C002
Top to Bottom: 1x3, 1x4, 1x5, 1x6, 1x7, 1x8, 1x9, 1x10 (LEDs)
C002
Top to Bottom: 1x3, 1x4, 1x5, 1x6, 1x7, 1x8, 1x9, 1x10 (LEDs)
Figure 32. Boost Efficiency vs VIN
Three String, L=22µH, 500kHz
90%
88%
88%
86%
86%
84%
84%
82%
80%
78%
76%
82%
80%
78%
76%
74%
74%
72%
72%
70%
0.00
Three String, L=22µH, 1MHz
90%
EFFICIENCY (%)
EFFICIENCY (%)
Figure 33. Boost Efficiency vs VIN
70%
12.00
24.00
36.00
48.00
60.00
0
ILED (mA)
12
24
36
48
60
ILED (mA)
C002
Top to Bottom: 3x3, 3x4, 3x5, 3x6, 3x7 (LEDs)
C002
Top to Bottom: 3x3, 3x4, 3x5, 3x6, 3x7 (LEDs)
Figure 34. Boost Efficiency vs ILED
Figure 35. Boost Efficiency vs ILED
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VIN = 3.6 V, full-scale current = 20.2 mA, LEDs are WLEDs part # SML-312WBCW(A), Typical Application Circuit , TA = 25°C
unless otherwise specified. Efficiency is VOUT × (IHVLED1 + IHVLED2 + IHVLED3)/(VIN × IIN), matching curves are (ΔILED_MAX/ILED_AVE).
Two String, L=22µH, 500kHz
Two String, L=22µH, 1MHz
90%
88%
88%
86%
86%
84%
84%
EFFICIENCY (%)
EFFICIENCY (%)
90%
82%
80%
78%
76%
82%
80%
78%
76%
74%
74%
72%
72%
70%
70%
0
12
24
36
48
0
12
ILED (mA)
24
36
48
ILED (mA)
C002
Top to Bottom: 2x3, 2x4, 2x5, 2x6, 2x7, 2x8, 2x9, 2x10 (LEDs)
C002
Top to Bottom: 2x3, 2x4, 2x5, 2x6, 2x7, 2x8, 2x9, 2x10 (LEDs)
Figure 36. Boost Efficiency vs ILED
Three String, L=10µH, 500kHz
90%
88%
88%
86%
86%
84%
84%
82%
80%
78%
76%
82%
80%
78%
76%
74%
74%
72%
72%
70%
0.00
Three String, L=10µH, 1MHz
90%
EFFICIENCY (%)
EFFICIENCY (%)
Figure 37. Boost Efficiency vs ILED
70%
12.00
24.00
36.00
48.00
0
60.00
12
24
36
48
60
ILED (mA)
ILED (mA)
C002
C002
Top to Bottom: 3x3, 3x4, 3x5, 3x6, 3x7 (LEDs)
Top to Bottom: 3x3, 3x4, 3x5, 3x6, 3x7 (LEDs)
Figure 39. Boost Efficiency vs ILED
Figure 38. Boost Efficiency vs ILED
Two String, L=10µH, 500kHz
Two String, L=10µH, 1MHz
90%
88%
88%
86%
86%
84%
84%
EFFICIENCY (%)
EFFICIENCY (%)
90%
82%
80%
78%
76%
82%
80%
78%
76%
74%
74%
72%
72%
70%
70%
0
12
24
36
48
0
ILED (mA)
12
24
36
C002
Top to Bottom: 2x3, 2x4, 2x5, 2x6, 2x7, 2x8, 2x9, 2x10 (LEDs)
C002
Top to Bottom: 2x3, 2x4, 2x5, 2x6, 2x7, 2x8, 2x9, 2x10 (LEDs)
Figure 40. Boost Efficiency vs ILED
28
48
ILED (mA)
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Figure 41. Boost Efficiency vs ILED
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VIN = 3.6 V, full-scale current = 20.2 mA, LEDs are WLEDs part # SML-312WBCW(A), Typical Application Circuit , TA = 25°C
unless otherwise specified. Efficiency is VOUT × (IHVLED1 + IHVLED2 + IHVLED3)/(VIN × IIN), matching curves are (ΔILED_MAX/ILED_AVE).
Three String, L=4.7µH, 500kHz
88%
88%
86%
86%
84%
84%
82%
80%
78%
76%
82%
80%
78%
76%
74%
74%
72%
72%
70%
0.00
Three String, L=4.7µH, 1MHz
90%
EFFICIENCY (%)
EFFICIENCY (%)
90%
70%
12.00
24.00
36.00
48.00
60.00
0
12
24
ILED (mA)
36
48
60
ILED (mA)
C002
Top to Bottom: 3x3, 3x4, 3x5, 3x6, 3x7 (LEDs)
C002
Top to Bottom: 3x3, 3x4, 3x5, 3x6, 3x7 (LEDs)
Figure 42. Boost Efficiency vs ILED
Two String, L=4.7µH, 500kHz
90%
Two String, L=4.7µH, 1MHz
90%
88%
88%
86%
86%
84%
84%
EFFICIENCY (%)
EFFICIENCY (%)
Figure 43. Boost Efficiency vs ILED
82%
80%
78%
76%
82%
80%
78%
76%
74%
74%
72%
72%
70%
70%
0
12
24
36
0
48
12
24
36
48
ILED (mA)
ILED (mA)
C002
C002
Top to Bottom: 2x3, 2x4, 2x5, 2x6, 2x7, 2x8, 2x9, 2x10 (LEDs)
Top to Bottom: 2x3, 2x4, 2x5, 2x6, 2x7, 2x8, 2x9, 2x10 (LEDs)
Figure 45. Boost Efficiency vs ILED
Figure 44. Boost Efficiency vs ILED
100
7.00%
m1-2
m2-3
m3-1
6.00%
5.00%
MATCHING (%)
CURRENT (mA)
10
1
0.1
4.00%
3.00%
2.00%
1.00%
0.00%
0.01
-1.00%
2048
1920
1792
1664
1536
1408
1280
1152
1024
896
768
640
512
384
256
128
0
2048
1920
1792
1664
1536
1408
1280
1152
1024
896
768
640
512
384
256
128
0
BRIGHTNESS CODE
BRIGHTNESS CODE
C001
Exponential Mapping
C001
Exponential Mapping
Figure 46. HVLED Current vs. Brightness Code
Figure 47. HVLED Matching Vs. Brightness Code
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VIN = 3.6 V, full-scale current = 20.2 mA, LEDs are WLEDs part # SML-312WBCW(A), Typical Application Circuit , TA = 25°C
unless otherwise specified. Efficiency is VOUT × (IHVLED1 + IHVLED2 + IHVLED3)/(VIN × IIN), matching curves are (ΔILED_MAX/ILED_AVE).
7.00%
30.0
28.0
26.0
24.0
22.0
20.0
18.0
16.0
14.0
12.0
10.0
8.0
6.0
4.0
2.0
0.0
m1-2
m2-3
m3-1
6.00%
LED CURRENT (mA)
MATCHING (%)
5.00%
4.00%
3.00%
2.00%
1.00%
0.00%
0.40
0.35
0.30
0.25
0.20
0.15
0.10
2048
1920
1792
1664
1536
1408
1280
1152
1024
896
768
640
512
384
256
128
0
0.05
0.00
-1.00%
BRIGHTNESS CODE
-40C
25C
90C
VHR (V)
C001
C001
Linear Mapping
Figure 48. HVLED Matching Vs. Brightness Code
Figure 49. HVLED Current vs. Current Sink Headroom
Voltage
1.70
1.01
1.00
1.50
0.99
PEAK CURRENT (A)
1.10
0.90
0.95
0.94
0.93
0.92
90C
25C
-40C
0.91
0.90
Figure 50. Shutdown Current vs. VIN
5.50
VIN (V)
C001
5.25
5.00
4.75
4.50
4.25
4.00
3.75
3.50
3.00
5.50
5.25
5.00
4.75
4.50
4.25
4.00
3.75
3.50
3.25
3.00
2.75
2.50
VIN (V)
2.75
0.50
0.96
3.25
90C
-40C
25C
0.70
0.97
2.50
SHUTDOWN CURRENT (uA)
0.98
1.30
C001
Figure 51. Open Loop Current Limit vs. VIN
100.00%
RIPPLE CURRENT (%)
10.00%
1.00%
0.10%
0.01%
10000
8000
6000
4000
2000
0
PWM FREQUENCY (Hz)
8s2p LED configuration
C001
Figure 52. Led Current Ripple vs FPWM
30
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Figure 53. Start-up Response
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VIN = 3.6 V, full-scale current = 20.2 mA, LEDs are WLEDs part # SML-312WBCW(A), Typical Application Circuit , TA = 25°C
unless otherwise specified. Efficiency is VOUT × (IHVLED1 + IHVLED2 + IHVLED3)/(VIN × IIN), matching curves are (ΔILED_MAX/ILED_AVE).
25.00
LED CURRENT (mA)
20.00
15.00
10.00
5.00
Max
Typ
Min
0.00
100.0%
87.5%
75.0%
62.5%
50.0%
37.5%
25.0%
12.5%
0.0%
PWM DUTY CYCLE (%)
Figure 54. Response To Step Change In PWM Input Duty
Cycle
C001
Figure 55. HVLED Current Vs PWM Input Duty Cycle
Figure 56. Line Step Response
8.3 Initialization Set Up
Table 25 illustrates the minimum number of register writes required for a two-parallel, seven-series LED
configuration. This example uses the default settings for ramp times (2048 µsec), mapping mode (exponential)
and full-scale current (20.2 mA). In this mode of operation the LM3697 controls the brightness LSB's to ramp
between the 8-bit MSB brightness levels providing 11-bit dimming while requiring only 8-bit commands from the
host controller.
Table 25. Control Bank A, 8-Bit Control, Two-String, Seven Series LED Configuration Example
REGISTER NAME
ADDRESS
DATA
DESCRIPTION
HVLED Current Sink Output
Configuration
0x10
0x04
HVLED1 & 2 assigned to Control Bank A
HVLED Current Sink Feedback
Enables
0x19
0x03
Enable feedback on HVLED1 & 2, disable feedback on HVLED3
OVP = 32V, ƒsw = 500 kHz
Boost Control
0x1A
0x04
Control Bank Enables
0x24
0x01
Enable Control Bank A
Control A Brightness LSB
0x20
0x00
Control A Brightness LSB written only once
Control A Brightness MSB
0x21
User Value
Control A Brightness MSB updated as required
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Table 26 illustrates the minimum number of register writes required for a two-parallel, six-series LED
configuration with PWM Enabled. This example uses the default settings for ramp times (2048 µsec), mapping
mode (exponential) and full-scale current (20.2 mA). In this mode of operation the host controller must update
both the brightness LSB and MSB registers whenever a brightness change is required.
Table 26. Control Bank A, 11-Bit Control, Two-String, Six Series LED Configuration Example
REGISTER NAME
ADDRESS
DATA
DESCRIPTION
HVLED Current Sink Output
Configuration
0x10
0x04
HVLED1 & 2 assigned to Control Bank A
HVLED Current Sink Feedback
Enables
0x19
0x03
Enable feedback on HVLED1 & 2, disable feedback on HVLED3
Boost Control
0x1A
0x02
OVP = 24 V, ƒsw = 500 kHz
PWM Configuration
0x1C
0x0D
PWM Zero Detect = Enabled, PWM Polarity = Active HIgh, Control
B PWM = Disabled, Control A PWM = Enabled
Control Bank Enables
0x24
0x01
Enable Control Bank A
Control A Brightness LSB
0x20
User Value
Control A Brightness LSB updated as required
(NOTE: The Brightness LSB change does not take effect until the
Brightness MSB register is written.)
Control A Brightness MSB
0x21
User Value
Control A Brightness MSB updated as required
(NOTE: Anytime the Brightness LSB is changed the Brightness
MSB must be written for the Brightness LSB change to take effect.)
9 Power Supply Recommendations
The LM3697 is designed to operate from an input supply range of 2.7 V to 5.5 V. This input supply must be well
regulated and provide the peak current required by the LED configuration and inductor selected.
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10 Layout
10.1 Layout Guidelines
The LM3697 device's inductive boost converter sees a high switched voltage (up to VOVP) at the SW pin, and a
step current (up to ICL_BOOST) through the Schottky diode and output capacitor each switching cycle. The high
switching voltage can create interference into nearby nodes due to electric field coupling (I = CdV/dt). The large
step current through the diode and the output capacitor can cause a large voltage spike at the SW pin and the
OVP pin due to parasitic inductance in the step current conducting path (V = Ldi/dt). Board layout guidelines are
geared towards minimizing this electric field coupling and conducted noise. Figure 57 highlights these two noisegenerating components.
Voltage Spike
(VSPIKE)
VOUT + VF Schottky
Pulsed voltage at SW
IPEAK
Current through
Schottky and
COUT
IAVE = IIN
Current through
Inductor
Parasitic
Circuit Board
Inductances
Affected Node
due to Capacitive Coupling
LCD Display
Cp1
L
Lp1
D1
Lp2
Up to 40V
2.7 V to 5.5 V
COUT
IN
SW
Lp3
CIN
LM3697
PWM
OVP
HWEN
SCL
SDA
HVLED1
HVLED2
HVLED3
GND
Figure 57. LM3697 Inductive Boost Converter Showing Pulsed Voltage at SW (High Dv/Dt) and Current
Through Schottky And COUT (High Di/Dt)
The following list details the main (layout sensitive) areas of the LM3697 device’s inductive boost converter in
order of decreasing importance:
1. Output Capacitor
– Schottky Cathode to COUT+
– COUT− to GND
2. Schottky Diode
– SW pin to Schottky Anode
– Schottky Cathode to COUT+
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Layout Guidelines (continued)
3. Inductor
– SW Node PCB capacitance to other traces
4. Input Capacitor
– CIN+ to IN terminal
10.1.1 Boost Output Capacitor Placement
Because the output capacitor is in the path of the inductor current discharge path it detects a high-current step
from 0 to IPEAK each time the switch turns off and the Schottky diode turns on. Any inductance along this series
path from the cathode of the diode through COUT and back into the LM3697 device's GND pin contributes to
voltage spikes (VSPIKE = LP_ × di/dt) at SW and OUT. These spikes can potentially over-voltage the SW pin, or
feed through to GND. To avoid this, COUT+ must be connected as close as possible to the cathode of the
Schottky diode, and COUT− must be connected as close as possible to the LM3697 device's GND bump. The
best placement for COUT is on the same layer as the LM3697 in order to avoid any vias that can add excessive
series inductance.
10.1.2 Schottky Diode Placement
In the LM3697 device’s boost circuit the Schottky diode is in the path of the inductor current discharge. As a
result the Schottky diode sees a high-current step from 0 to IPEAK each time the switch turns off and the diode
turns on. Any inductance in series with the diode causes a voltage spike (VSPIKE = LP_ × di/dt) at SW and OUT.
This can potentially over-voltage the SW pin, or feed through to VOUT and through the output capacitor and into
GND. Connecting the anode of the diode as close as possible to the SW pin and the cathode of the diode as
close as possible to COUT and reduces the inductance (LP_) and minimize these voltage spikes.
10.1.3 Inductor Placement
The node where the inductor connects to the LM3697 device’s SW pin has 2 issues. First, a large switched
voltage (0 to VOUT + VF_SCHOTTKY) appears on this node every switching cycle. This switched voltage can be
capacitively coupled into nearby nodes. Second, there is a relatively large current (input current) on the traces
connecting the input supply to the inductor and connecting the inductor to the SW pin. Any resistance in this path
can cause voltage drops that can negatively affect efficiency and reduce the input operating voltage range.
To reduce the capacitive coupling of the signal on SW into nearby traces, the SW pin-to-inductor connection
must be minimized in area. This limits the PCB capacitance from SW to other traces. Additionally, highimpedance nodes that are more susceptible to electric field coupling need to be routed away from SW and not
directly adjacent or beneath. This is especially true for traces such as SCL, SDA, HWEN, and PWM. A GND
plane placed directly below SW dramatically reduces the capacitance from SW into nearby traces.
Lastly, limit the trace resistance of the VIN-to-inductor connection and from the inductor to SW connection, by
use of short, wide traces.
10.1.4 Boost Input Capacitor Placement
For the LM3697 device’s boost converter, the input capacitor filters the inductor current ripple and the internal
MOSFET driver currents during turnon of the internal power switch. The driver current requirement can range
from 50 mA at 2.7 V to over 200 mA at 5.5 V with fast durations of approximately 10 ns to 20 ns. This appears
as high di/dt current pulses coming from the input capacitor each time the switch turns on. Close placement of
the input capacitor to the IN pin and to the GND in is critical because any series inductance between IN and
CIN+ or CIN− and GND can create voltage spikes that could appear on the VIN supply line and in the GND
plane.
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Layout Guidelines (continued)
Close placement of the input bypass capacitor at the input side of the inductor is also critical. The source
impedance (inductance and resistance) from the input supply, along with the input capacitor of the LM3697,
forms a series RLC circuit. If the output resistance from the source (RS) is low enough the circuit is underdamped
and has a resonant frequency (typically the case). Depending on the size of LS the resonant frequency could
occur below, close to, or above the switching frequency of the device. This can cause the supply current ripple to
be:
1. Approximately equal to the inductor current ripple when the resonant frequency occurs well above the
LM3697 device's switching frequency;
2. Greater than the inductor current ripple when the resonant frequency occurs near the switching frequency; or
3. Less than the inductor current ripple when the resonant frequency occurs well below the switching frequency.
Figure 58 shows the series RLC circuit formed from the output impedance of the supply and the input capacitor.
The circuit is redrawn for the AC case where the VIN supply is replaced with a short to GND, and the LM3697 +
Inductor is replaced with a current source (ΔIL). Equation 1 is the criteria for an underdamped response. Equation
2 is the resonant frequency. Equation 3 is the approximated supply current ripple as a function of LS, RS, and
CIN.
As an example, consider a 3.6-V supply with 0.1 Ω of series resistance connected to CIN through 50 nH of
connecting traces. This results in an underdamped input-filter circuit with a resonant frequency of 712 kHz.
Because both the 1-MHz and 500-kHz switching frequency options lie close to the resonant frequency of the
input filter, the supply current ripple is probably larger than the inductor current ripple. In this case, using
equation 3, the supply current ripple can be approximated as 1.68 times the inductor current ripple (using a 500kHz switching frequency) and 0.86 times the inductor current ripple using a 1-MHz switching frequency.
Increasing the series inductance (LS) to 500 nH causes the resonant frequency to move to around 225 kHz, and
the supply current ripple to be approximately 0.25 times the inductor current ripple (500-kHz switching frequency)
and 0.053 times for a 1-MHz switching frequency.
'IL
ISUPPLY
RS
LS
L
SW
+
IN
VIN Supply
LM3697
-
CIN
ISUPPLY
LS
RS
CIN
'IL
2
1.
RS
1
>
LS x CIN 4 x LS2
2. f RESONANT =
1
2S LS x CIN
3. I SUPPLYRIPP LE | 'IL x
1
2S x 500 kHz x CIN
2
·
§
1
2
¸
RS + ¨¨2S x 500 kHz x LS ¸
2
S
x
500
kHz
x
C
IN
¹
©
Figure 58. Input RLC Network
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10.2 Layout Example
Top Layer
Inner or
Bottom Layer
Inductor
4.57 mm
Input Cap
VIA
Output Cap
Diode
6.35 mm
Figure 59. LM3697 Layout Example
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11 Device and Documentation Support
11.1 Device Support
11.1.1 Third-Party Products Disclaimer
TI'S PUBLICATION OF INFORMATION REGARDING THIRD-PARTY PRODUCTS OR SERVICES DOES NOT
CONSTITUTE AN ENDORSEMENT REGARDING THE SUITABILITY OF SUCH PRODUCTS OR SERVICES
OR A WARRANTY, REPRESENTATION OR ENDORSEMENT OF SUCH PRODUCTS OR SERVICES, EITHER
ALONE OR IN COMBINATION WITH ANY TI PRODUCT OR SERVICE.
11.2 Related Documentation
For additional information, see the following:
TI Application Note DSBGA Wafer Level Chip Scale Package (SNVA009)
11.3 Community Resources
The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective
contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of
Use.
TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration
among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help
solve problems with fellow engineers.
Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and
contact information for technical support.
11.4 Trademarks
E2E is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
11.5 Electrostatic Discharge Caution
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
11.6 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
12 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
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PACKAGE OPTION ADDENDUM
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1-Oct-2015
PACKAGING INFORMATION
Orderable Device
Status
(1)
LM3697YFQR
ACTIVE
Package Type Package Pins Package
Drawing
Qty
DSBGA
YFQ
12
3000
Eco Plan
Lead/Ball Finish
MSL Peak Temp
(2)
(6)
(3)
Green (RoHS
& no Sb/Br)
SNAGCU
Level-1-260C-UNLIM
Op Temp (°C)
Device Marking
(4/5)
-40 to 125
D8
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3)
MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4)
There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5)
Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6)
Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish
value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 1
Samples
PACKAGE OPTION ADDENDUM
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Addendum-Page 2
PACKAGE MATERIALS INFORMATION
www.ti.com
1-Oct-2015
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0
Diameter Width (mm)
(mm) W1 (mm)
LM3697YFQR
DSBGA
YFQ
12
3000
178.0
8.4
LM3697YFQR
DSBGA
YFQ
12
3000
178.0
8.4
Pack Materials-Page 1
B0
(mm)
K0
(mm)
P1
(mm)
W
Pin1
(mm) Quadrant
1.35
1.75
0.76
4.0
8.0
Q1
1.38
1.78
0.78
4.0
8.0
Q1
PACKAGE MATERIALS INFORMATION
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1-Oct-2015
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
LM3697YFQR
DSBGA
YFQ
12
3000
210.0
185.0
35.0
LM3697YFQR
DSBGA
YFQ
12
3000
220.0
220.0
35.0
Pack Materials-Page 2
MECHANICAL DATA
YFQ0012xxx
D
0.600
±0.075
E
TMD12XXX (Rev B)
D: Max = 1.64 mm, Min = 1.58 mm
E: Max = 1.29 mm, Min = 1.23 mm
4215079/A
NOTES:
A. All linear dimensions are in millimeters. Dimensioning and tolerancing per ASME Y14.5M-1994.
B. This drawing is subject to change without notice.
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12/12
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Applications
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DLP® Products
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dsp.ti.com
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Logic
logic.ti.com
Security
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Microcontrollers
microcontroller.ti.com
Video and Imaging
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RFID
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www.ti.com/omap
TI E2E Community
e2e.ti.com
Wireless Connectivity
www.ti.com/wirelessconnectivity
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