FAN5776 — Synchronous Boost and Series/Parallel 10

FAN5776 — Synchronous Boost and Series/Parallel 10
Is Now Part of
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FAN5776
Synchronous Boost and Series / Parallel 10-LED Driver
Features
Description


Synchronous Current-Mode Boost Converter


5 LED Outputs: High-Side Current Sources
The FAN5776 is a synchronous, constant-current LED driver
capable of efficiently driving up to ten LEDs in a five-string,
two-series LEDs per string configuration. Optimized for small
form-factor applications, the 1.8 MHz switching frequency
allows the use of tiny chip inductors and capacitors.
Drives up to 10 LEDs at 25 mA Each in a Configuration of
5 Strings of 2 LEDs in Series
Two Default Groups of 3x2-LED Channels and 2x2-LED
Channels with Individual Enable and PWM Dimming
Control to Support Various Lighting Applications, such as:
o Backlighting of Dual-LCD Displays, LCD Display Plus
Keypad Illumination
 Boost PFM Mode Maximizes Efficiency Under Light Loads
 2.3 V to 5.5 V Input Voltage Range
 1.8 MHz Switching Frequency
 Input Under-Voltage Lockout (UVLO)
 Output Over-Voltage Protection (OVP)
 Short-Circuit and Thermal Shutdown (TSD) Protection
 12-Bump, 0.4 mm Pitch, 1.42 x 1.66 x 0.50 mm WLCSP
Applications
For safety, the device features integrated over-voltage, shortcircuit, and thermal shutdown protections. In addition, input
under-voltage lockout protection is triggered if the battery
voltage is too low.
The FAN5776 is comprised of low-dropout, high-side current
sources, enabling a high efficiency delivery of power from the
battery to the LEDs. The LED current control is established
with a series RSET resistor, which is connected between the
internal voltage reference on the chip and ground.
During operation, FAN5776 holds the boost regulator’s voltage
on COUT during the off cycle of the PWM dimming, which helps
minimize audible noise.
The FAN5776 is available in a very low profile, small-formfactors 1.42 x 1.66 x 0.50 mm, 12-bump WLCSP package that
is “green” and RoHS compliant.
 Mid-and Large-Size LCD Modules
 Cellular Mobile Handsets, Smart Phones
 Smartbooks, Netbooks, MIDs
 Pocket PCs
 WLAN DC-DC Converter Modules
 PDA, DSC, PMP, and MP3 Players
Ordering Information
Part Number
Temperature
Range
FAN5776UCX
-40 to 85°C
© 2010 Fairchild Semiconductor Corporation
FAN5776 • Rev. 1.1.0
Package
12-Bump, Wafer-Level Chip-Scale Package (WLCSP)
1.42 x 1.66 x 0.50 mm, 0.40 mm Pitch
Packing
Tape and Reel
www.fairchildsemi.com
FAN5776 — Synchronous Boost and Series/Parallel 10-LED Driver
October 2013
Q2
SW
VOUT
COUT
L1
Q1
LED1
LED2
VIN
CURRENT
SOURCES
MODULATOR
LOGIC
AND CONTROL
CIN
EN13
DIGITAL CONTROL
OF STARTUP
EN45
LED3
LED4
LED5
FB
GND
ISET
Group 2
Group 1
RSET
Figure 1.
Table 1.
Typical Application Block Diagram
Recommended External Components
Component
Description
Vendor
L1
IL1 = 500 mA
Various
RSET
1% or Better
Various
R
20
COUT
10 F X5R or Better
Murata
GRM219R61A116UE82
C
4.2
CIN
2.2 F X5R or Better
Murata
GRM155R61A225KE95
C
© 2010 Fairchild Semiconductor Corporation
FAN5776 • Rev. 1.1.0
Parameter
Min.
Typ.
L
2.45
4.70
R
10.0
2.2
Max.
Units
H
0.30

200
k
20.0
F
F
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2
FAN5776 — Synchronous Boost and Series/Parallel 10-LED Driver
Block Diagram
VIN
ISET
LED1
A1
A2
A3
EN13
B1
B2
B3
GND
C1
C2
C3
A3
A2
A1
LED2
B3
B2
B1
LED3
C3
C2
C1
D3
D2
D1
EN45
LED5
D1
SW
Figure 2.
D2
D3
VOUT LED4
Top View (Bumps Face Down)
Figure 3.
Bottom View (Bumps Face Up)
Pin Definitions
Pin #
Name
Description
A1
VIN
Input voltage
A2
ISET
The LED current is set by tying this pin through the resistor, R SET, to GND. The resistor value sets
the current for the LED strings.
A3
LED1
LED string #1 output
B1
EN13
Enable/PWM pin for LED1, LED2, and LED3. A logic LOW on this pin turns off the LED drivers in
LED1, LED2, and LED3. The IC goes to shutdown 30 ms after both enable pins (EN13 and EN45)
are set LOW. It is connected to an internal pull-down resistor of 250 kΩ.
B2
EN45
Enable/PWM pin for LED4 and LED5. A logic LOW on this pin turns off the LED drivers in LED4
and LED5. The IC goes to shutdown 30 ms after both enable pins (EN13 and EN45) are set LOW.
It is connected to an internal pull-down resistor of 250 kΩ.
B3
LED2
LED string #2 output
C1
GND
Ground. All power and analog signals are referenced to this pin.
C2
LED5
LED string #5 output
C3
LED3
LED string #3 output
D1
SW
D2
VOUT
Boost output voltage used to supply the LED current sources. This voltage is regulated to the
minimum value required to ensure adequate voltage across all active LED current sources.
D3
LED4
LED string #4 output
Switching Node. Tie inductor L1 from VIN to this pin.
© 2010 Fairchild Semiconductor Corporation
FAN5776 • Rev. 1.1.0
www.fairchildsemi.com
3
FAN5776 — Synchronous Boost and Series/Parallel 10-LED Driver
Pin Configuration
Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be operable above
the recommended operating conditions and stressing the parts to these levels is not recommended. In addition, extended
exposure to stresses above the recommended operating conditions may affect device reliability. The absolute maximum ratings
are stress ratings only.
Symbol Parameter
Min.
Max.
Unit
Supply Voltage
-0.3
6.0
V
VISET
ISET Voltage
-0.3
VIN + 0.3
V
VEN
EN13 and EN45 Pin Maximum Voltage
-0.3
6.0
V
VOVP
VOUT, SW, and LEDx Drive Pins Maximum Voltage
-0.3
11.0
V
ESD
Electrostatic Discharge Protection Human Body Model per JESD22-A114
Level
Charged Device Model per JESD22-C101
VIN
2
kV
1
TA
Operating Ambient Temperature
–40
+85
°C
TJ
Junction Temperature
–40
+150
°C
TSTG
Storage Temperature
–65
+150
°C
+260
°C
TL
Lead Soldering Temperature, 10 Seconds
Recommended Operating Conditions
The Recommended Operating Conditions table defines the conditions for actual device operation. Recommended operating
conditions are specified to ensure optimal performance to the datasheet specifications. Fairchild does not recommend exceeding
them or designing to absolute maximum ratings.
Symbol Parameter
VIN
VOUT
VIN Supply Voltage
(1)
Min.
Typ.
Max.
Unit
2.3
3.7
5.5
V
VOUT Voltage
3.5
8.5
V
Full Scale LED Current per Channel
2.5
25.0
mA
TA
Ambient Temperature
–40
+85
°C
TJ
Junction Temperature
–40
+125
°C
ILED(FS)
Note:
1. The minimum VOUT must be 3.5 V to guarantee a maximum LED current of 25 mA for each LED pin. Otherwise the device
internally sets a minimum VOUT to VIN + 0.3 V, and the LED driver dropout is increased accordingly (if LED VF < VIN,
where VF = VOUT - 0.3 V).
Thermal Properties
Junction-to-ambient thermal resistance is a function of application and board layout. This data is measured with four-layer 2s2p
boards in accordance to JEDEC standard JESD51. Special attention must be paid not to exceed junction temperature TJ(max) at a
given ambient temperate TA.
Symbol Parameter
JA
Min.
Junction-to-Ambient Thermal Resistance
Typ.
90
Max.
Unit
°C/W

© 2010 Fairchild Semiconductor Corporation
FAN5776 • Rev. 1.1.0
www.fairchildsemi.com
4
FAN5776 — Synchronous Boost and Series/Parallel 10-LED Driver
Absolute Maximum Ratings
Unless otherwise specified: VIN = 2.3 V to 5.5 V, TA = -40C to +85C, and EN13 and EN45 = “1.” Typical values are VIN = 3.7 V,
TA = 25C, VOUT = 6.8 V, ILED1-5 = 20 mA. Circuit and components are according to Figure 1.
Symbol
Parameter
Condition
Min.
Typ.
Max.
Unit
0.1
4.0
A
2.1
1.9
200
2.2
V
V
mV
Power Supplies
ISD
VUVLO
VUVHYST
Device Disabled, (EN13 = EN45 = “0”),
VIN = 2.3 V to 4.5 V
Rising VIN
Under-Voltage Lockout
Threshold
Falling VIN
Under-Voltage Lockout Hysteresis
Shutdown Current
1.8
Oscillator
fSW
Frequency
PWM Mode CCM
1.8
MHz
Boost Regulator
ILIM-PK
ISOFT-PK
ILOAD
Peak Switch Current Limit
Soft-Start Peak Switch
Current
Maximum Continuous
(3)
Output Current
(2)
Open Loop, VIN = 2.5 V to 5.5 V
445
Open Loop
525
640
250
VIN > 2.5 V
mA
mA
100
mA
LED Current Driver Characteristics
ILED/ILED
VLED_DO
fPWM
Line Transient Response to
(3)
VIN Variations
LED Driver Drop-Out Voltage
(3)
LED PWM Frequency
ILED_MATCH LED Current Matching
(3)
Relative Response to 350 mV Pulses
10
Response to 350 mV Pulses Integrated
Over 20 ms Period
1
(5)
290
100
Variation between Different
ILED1 – ILED5 Currents.
Matching LED Pin Voltage
(4)
Difference < 250 mV
ILED = 2.5 mA
to 10 mA
2.0
5.0
ILED = 10 mA
to 25 mA
1.0
3.5
10
PWM  25/255, 300 Hz
2
LED Current Linearity
ILED
Absolute LED Current
Accuracy
LED1 – LED5
Peak-to-Peak LED Current
(3)
Ripple
VLED_DO  0.6 V (Typical 0.29 V),
fPWM = 300 Hz, Measurement BW = 10 MHz
LED Driver Leakage
In OFF State
ILEAKAGE
VISET
mV
Hz
%
1/255  PWM  24/255, 300 Hz
ILINEARITY
ILED_RIPPLE
800
%
ILED = 2.5 mA
to 5 mA
ILED = 5 mA
to 25 mA
%
15.0
%
7.5
0.4
ISET Voltage
1.2
mAP-P
0.5
µA
1.20
V
Logic Control
VIL
VIH
REN13
Logic LOW Threshold
Logic HIGH Threshold
EN13 Pull-Down Resistor
REN45
EN45 Pull-Down Resistor
0.5
1.05
V
V
250
k
250
k
Continued on the following page…
© 2010 Fairchild Semiconductor Corporation
FAN5776 • Rev. 1.1.0
www.fairchildsemi.com
5
FAN5776 — Synchronous Boost and Series/Parallel 10-LED Driver
Electrical Specifications
Unless otherwise specified: VIN = 2.3 V to 5.5 V, TA = -40C to +85C, and EN13 and EN45 = “1.” Typical values are VIN = 3.7 V,
VOUT = 6.8 V, TA = 25C, ILED1-5 = 20 mA. Circuit and components are according to Figure 1.
Symbol
Parameter
Condition
Min.
Typ.
Max.
Unit
Protection
TTSD
Over-Temperature Shutdown
150
°C
THYS
Over-Temperature Hysteresis
25
°C
VOV-RISE
VOUT Over-Voltage Rising Threshold
VOV-FALL
VOUT Over-Voltage Falling Threshold
VOV-HYS
Hysteresis
VLED(SC)
LED Short Circuit Protection Threshold
ILED-SHORT Shorted LED Current
8.25
0.7
LED Short-Circuit Protection Threshold
Tripped
9.0
V
8.60
V
400
mV
1.0
1.4
V
1
µA
Notes:
2. In closed loop operation, the inductor current (IL) is 30 mA to 40 mA greater than ILIM-PK.
3. Guaranteed by characterization and design.
4. For the LED outputs, the following are determined: the maximum LED current in the group (MAX), the minimum LED
current in the group (MIN), and the average LED current of the group (AVG). Two matching numbers are calculated:
(MAX - AVG) / AVG and (AVG - MIN) / AVG. The larger number of the two (worst case) is considered the matching value
for the group. The matching value for a given part is considered to be the highest matching value of the two groups.
The typical specification provided is the most likely norm of the matching value for all parts.
5. LED driver drop-out voltage is the smallest voltage across all the LED channels.
© 2010 Fairchild Semiconductor Corporation
FAN5776 • Rev. 1.1.0
www.fairchildsemi.com
6
FAN5776 — Synchronous Boost and Series/Parallel 10-LED Driver
Electrical Specifications
VIN = 3.7 V, TA = 25C, ILED = 5 x 20 mA, VOUT = 6.8 V, L1 = 4.7 µH, and COUT = 10 µF (unless otherwise specified).
Boost Efficiency (%)
Boost Efficiency (%)
95
VOUT = 6.8 V
90
VOUT = 5.8 V
85
VOUT = 7.8 V
80
VOUT = 8.8 V
75
70
65
10
30
50
70
90
110
95
SILED = 125 mA
SILED = 100 mA
90
SILED = 75 mA
85
SILED = 50 mA
80
75
70
SILED = 12 mA
65
2.50
130
3.50
4.50
VIN (V)
Total Output Current (mA)
Figure 4.
Boost Efficiency vs. Output Current
vs. Output Voltage
Figure 5.
90
VOUT = 6.8 V
System Efficiency (%)
System Efficiency (%)
90
85
VOUT = 5.8 V
80
VOUT = 7.8 V
VOUT = 8.8 V
75
70
65
10
30
50
70
90
110
130
Boost Efficiency vs. Input Voltage
vs. Total LED Current
S ILED = 100 mA
85
SILED = 75 mA
S ILED = 50 mA
75
70
S ILED = 12 mA
65
2.50
Total Efficiency vs. Output Current
vs. Output Voltage
3.50
Figure 7.
VIN (V)
4.50
5.50
Total Efficiency vs. Input Voltage
vs. Total LED Current
125
Total LED Current (mA)
System Efficiency (%)
100
SILED = 125 mA
80
Total Output Current (mA)
Figure 6.
5.50
80
60
40
20
0
0
20
40
60
80
100
100
75
50
25
0
0
Total Efficiency vs. PWM Duty Cycle,
fPWM = 300 Hz
© 2010 Fairchild Semiconductor Corporation
FAN5776 • Rev. 1.1.0
40
60
80
100
PWM Duty Cycle (%)
Duty Cycle (%)
Figure 8.
20
Figure 9.
Total LED Current vs. PWM Duty Cycle,
ILED = 5 x 25 mA
www.fairchildsemi.com
7
FAN5776 — Synchronous Boost and Series/Parallel 10-LED Driver
Typical Characteristics
Total Output Current
(mA)
VIN = 3.7 V, TA = 25°C, ILED = 5 x 20 mA, VOUT = 6.8 V, L1 = 4.7 µH, COUT = 10 µF (unless otherwise specified).
130
500
VOUT = 5.8 V
ILED Ripple (µA)
120
VOUT = 7.8 V
110
VOUT = 6.8 V
100
VOUT = 8.8 V
90
80
70
2.50
3.50
4.50
300
100
-100
-300
-500
5.50
0
VIN (V)
5
10
15
20
Time (µs)
Figure 10. Maximum Output Current (ILED = 5 x 25 mA)
vs. Input Voltage vs. Output Voltage
Figure 11. LED Current Ripple
700
Current (mA)
VIN = 3.70V-3.35 V-3.70 V, slope 30 µs/V
500 mV/div
SILED
10 mA/div
650
600
550
500
2.5
3.0
3.5
Time Base 300µs/div
Figure 12. Line Transient Response
VIN = 3.70 - 3.35 V - 3.70 V with ILED = 5 x 25 mA
Total Output Current (mA)
Current (µA)
0.80
0.60
0.40
0.20
0.00
3.00
3.50
4.00
4.50
5.00
5.50
VIN (V)
5.0
5.5
150
120
90
60
30
0
0
50
100
150
200
RSET Resistance (k)
Figure 14. Shutdown Current vs. Input Voltage
© 2010 Fairchild Semiconductor Corporation
FAN5776 • Rev. 1.1.0
4.5
Figure 13. Peak Inductor Current Limit (Closed Loop)
vs. Input Voltage
1.00
2.50
4.0
VIN (V)
Figure 15. Total Output Current ILED vs. RSET
Resistor Value
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8
FAN5776 — Synchronous Boost and Series/Parallel 10-LED Driver
Typical Characteristics
VIN = 3.7 V, TA = 25°C, ILED = 5 x 20 mA, VOUT = 6.8 V, L1 = 4.7 µH, COUT = 10 µF (unless otherwise specified).
ILED CH1...CH5
10 mA/div
ILED CH1...CH3
100 mA/div
VOUT
1 V/div
VOUT
1 V/div
VSW
2 V/div
VIN
1 V/div
ISW
200 mA/div
EN13
1 V/div
Time Base 400 ns/div
Time Base 10 ms/div
Figure 16. Switch Waveform (VOUT, VSW, ISW)
Figure 17. Startup After Enable, Three
Strings Connected
ILED CH1...CH4
100 mA/div
ILED CH1...CH5
100 mA/div
VOUT
1 V/div
VOUT
1 V/div
VIN
1 V/div
VIN
1 V/div
EN13=EN45
1 V/div
EN13=EN45
1 V/div
Time Base 20 ms/div
Figure 18. Startup After Enable, Four Strings Connected
Time Base 10 ms/div
Figure 19. Startup After Enable, Five Strings Connected
ILED CH1...CH5
100 mA/div
ILED CH1...CH5
100 mA/div
VOUT
1 V/div
VOUT
1 V/div
VIN
1 V/div
EN15
1 V/div
EN45
1 V/div
EN13
1 V/div
Time Base 2 ms/div
Time Base 20 ms/div
Figure 20. LED PWM Startup, Five Strings Connected
© 2010 Fairchild Semiconductor Corporation
FAN5776 • Rev. 1.1.0
Figure 21. Startup After LED1-3 Enable Followed by
LED4-5 Enable
www.fairchildsemi.com
9
FAN5776 — Synchronous Boost and Series/Parallel 10-LED Driver
Typical Characteristics
VIN = 3.7 V, TA = 25°C, ILED = 5 x 20 mA, VOUT = 6.8 V, L1 = 4.7 µH, COUT = 10 µF (unless otherwise specified).
SILED
100 mA/div
SILED
100 mA/div
VOUT
50 mV/div
VOUT
50 mV/div
EN45
2 V/div
VLED1
2 V/div
VLED5
2 V/div
EN13
2 V/div
Time Base 400 µs/div
Time Base 400 µs/div
Figure 22. Asynchronous LED PWM, Two LEDs
per LED String
Figure 23. Asynchronous LED PWM, Two LEDs on
LED1-3 Strings, Single LED on LED4-5 Strings
SILED
100 mA/div
ILED CH1...CH5
100 mA/div
VOUT
50 mV/div
VOUT
1 V/div
VIN
1 V/div
EN45
2 V/div
EN13
2 V/div
EN15
1 V/div
Time Base 1 ms/div
Figure 24. Asynchronous LED PWM, All LED Outputs
Shorted Together for Common Load
See Figure 30
© 2010 Fairchild Semiconductor Corporation
FAN5776 • Rev. 1.1.0
Time Base 10 ms/div
Figure 25. Device Disabled, Five Strings Connected
www.fairchildsemi.com
10
FAN5776 — Synchronous Boost and Series/Parallel 10-LED Driver
Typical Characteristics
FAN5776 starts to step up or down to the appropriate
regulated voltage.
Overview
The FAN5776 is a 1.8 MHz synchronous step-up DC-DC
converter with integrated constant-current high-side LED
drivers capable of driving one to five LED strings up to 5 x
25 mA LED current.
2.
At least one LED string in a group is shorted to GND. VOUT
rises to 7.5 V while the shorted LED string is disabled and
the device starts to step up or down to regulated voltage.
The device starts when at least one LED string is utilized and
the appropriate EN pin is enabled. The device is disabled in
30 ms by setting both EN pins LOW.
3.
At least one LED string is floating or connected to VOUT.
VOUT rises to 9.0 V, the floating LED string is disabled, and
the device starts to step down to regulated voltage.
The VOUT voltage is internally set to 290 mV above the highest
LED string voltage, and it is sampled at every falling LED PWM
cycle. For 100% duty cycle, the LED-pin voltage is sampled
and the VOUT voltage is refined every 10 ms.
These functions work for each group independently. If all five
strings are utilized and EN13 is HIGH, VOUT rises to 7.5 V (case
1) and goes to the highest voltage required by LED1-3. Then
EN45 is raised and VOUT is stepped up again to 7.5 V and
regulates to highest voltage required by LED1-5.
The LED strings can be disabled by connecting them to VOUT
or shorting them to GND. They can also be left disconnected. If
the LED string is temporarily disabled or shorted, the device
must be re-enabled to enable the string again.
If VOUT cannot reach 7.5 V within 1.2 ms after an enable cycle,
the device stays disabled and a new enable cycle is required.
PWM Dimming
The LED drivers work independently and allow multiple LED
voltages, such that many types of LEDs can be driven at the
same time and some strings can be used to drive a single LED
while other channels are driving two LEDs in series. The VOUT
voltage is defined by the highest LED voltage and the LED
driver dropout voltage is increased to provide the LED string a
specific voltage. If the voltage difference between the LED
strings is large, the system efficiency may decrease.
A LED PWM signal of 100 Hz to 800 Hz can be applied to
EN13 and EN45 pins to control LED1-3 and LED4-5 light
intensity. The LED current is a linear function of the LED
PWM duty cycle from 100% down to 0.4%. The FAN5776
can be started by a PWM signal with a low duty cycle to
enable smooth startup. EN13 and EN45 pins can be
operated either synchronously or asynchronously, which
makes it possible to use the device to backlight two
separate displays at the same time.
LED Current
Under-Voltage Lockout (UVLO)
The LED string current is set by the resistor, RSET, between the
ISET and GND pins. The same current is applied to across all
strings such that total output current: IOUT = 5 x ILED = 5 x
20 mA = 100 mA if RSET = 25 kand all LED strings are used.
In general, the LED string current can be calculated as follows:
The Under-Voltage Lockout circuitry turns off all MOSFETs and
the device remains in a very low quiescent current state until
VIN has risen above the UVLO threshold.
Short-Circuit Protection (SCP)
𝐼𝐿𝐸𝐷
500
=
𝑅𝑆𝐸𝑇
The LED driver output current is limited to 0.5 µA or less when
a LED number pin voltage is below 1.0 V. This limit shall be
applied within one LED PWM cycle, or 10 ms, whichever
elapses first.
(1)
LED Current (mA)
25
Over-Voltage Protection (OVP)
20
When the regulator is active, it monitors the VOUT pin. If the
VOUT voltage reaches 9.0 V, the regulator stops switching until
the capacitor at VOUT discharges below 8.5 V.
15
10
LED-Open Detection
If VOUT is detected above >9.0 V, the LED voltages are
scanned. All LED pins with voltage greater than VOUT - 0.5 V
are disabled. If all LED pins’ voltages exceed 8.5 V and VOUT is
greater than 9.0 V, device is disabled and a new startup cycle
is required.
5
0
20
40
60
80 100 120 140 160 180 200
Resistor RSET (k)
Over-Current Protection (OCP)
The PWM converter is protected against overload through
cycle-by cycle current limit using a fixed internal limit.
Figure 26. LED Current vs. RSET Value
Startup
Thermal Shutdown
The three different startup functions depend on the system
configuration:
1.
When the die temperature exceeds 150°C, reset occurs and
remains in effect until the die cools to 125°C; at which time,
the circuit enters the normal soft-start sequence.
All LED strings are utilized: Setting one or both EN pins
HIGH enables the device and VOUT rises to 7.5 V.
© 2010 Fairchild Semiconductor Corporation
FAN5776 • Rev. 1.1.0
www.fairchildsemi.com
11
FAN5776 — Synchronous Boost and Series/Parallel 10-LED Driver
Circuit Description
External Component Selection
Four external components are required to power the
FAN5776: an inductor between the VIN and SW pins, storage
capacitor at the output, storage capacitor at the input, and
reference resistor at the ISET pin.
The inductor’s minimum inductance requirement is 2.45 µH
with an ESR ≤ 300 m at 500 mA bias current at 1.8 MHz
frequency. A lower inductance drops device efficiency, while a
higher inductance reduces output ripple.
The minimum capacitance for the output capacitor is 4.8 µF at
5 V. Note that the ceramic capacitor value depends on the DC
bias voltage. Check the datasheet of the capacitor to make
sure the capacitor meets all specifications.
Figure 28. Schematic for Recommended Layout
Startup Power Minimization
The FAN5776 is optimized to minimize startup power when
all five LED driver outputs are connected to LEDs. Where
some of the LED strings are not used due to smaller LCD
display size, the startup power can still be minimized.
Connecting the unused LED driver outputs to ground (GND)
prevents LED current drop during startup and VOUT starts at
7.5 V, which reduces power consumption. Secondly, the
unused LED driver outputs connected to GND are disabled
at startup, minimizing the leakage current to GND. If left
open the unused LED strings cause VOUT to rise to the OVP
voltage of 9.0 V instead of starting at 7.5 V. The device
detects an open circuit due to the unused LED strings and
therefore goes up to 9.0 V, then adjusts to a VOUT that is
appropriate to power the LED strings.
An input capacitor of 2.2 µF is recommended to improve
device’s transient behavior. Ensure the VIN supply voltage is
ripple-free for optimal device performance.
The reference resistor value is at least 20 k. The LED
current accuracy is defined by this resistor and a highprecision resistor with low temperature dependency is
recommended. To guarantee the FAN5776 performance and
achieve ILED maximum current of 25 mA, 20 k, ±1% or
better resistor must be used.
PCB Layout Guidelines
A separate ground plane is recommended to minimize noise.
Place the FAN5776 device, inductor (L), CIN and COUT
capacitors, and their interconnections on the same side of the
board. High-current paths from the supply voltage to the SW
pin via the inductor, and GND pin to ground plane, are
recommended as low resistance paths. Keep the VOUT-pinto-COUT-capacitor path as short as possible to minimize the
inductance of the VOUT-pin-to-COUT for low VOUT ripple
voltage. Minimize the SW pin capacitance to realize optimum
system efficiency. Keep the ISET-pin-to-RSET-resistor path
away from noisy signals (SW pin) to minimize crosstalk from
the SW pin to the ISET pin.
The device is also working to specification when un-used LED
drivers are connected to the VOUT pin or left floating.
Combined LCD Backlight and Blinker
Figure 29. Schematic for Screen Backlight and Blinker
The FAN5776 can be utilized for different lighting
applications by configuring it to suit the design requirements.
Each LED driver output is independent such that each output
can support a different output voltage while being controlled
simultaneously.
Configuring the FAN5776 with a different number of LEDs for
each output results in a lower system efficiency because the
outputs with a single LED have a higher dropout voltage
compared to the outputs with two LEDs in series. The system
efficiency (η) is calculated as follows:
Figure 27. Recommended PCB Layout
© 2010 Fairchild Semiconductor Corporation
FAN5776 • Rev. 1.1.0
www.fairchildsemi.com
12
FAN5776 — Synchronous Boost and Series/Parallel 10-LED Driver
Applications
𝜂 =
𝑖 =1
𝐼𝑖 𝑉𝑖
𝐼𝐼𝑁 𝑉𝐼𝑁
Figure 29 illustrates an application where the FAN5776 uses
three LED outputs (LED1 to LED3) with two LEDs in series
per channel to backlight the main LCD display, while LED5
powers a single LED for blinking functionality. LED4 is unused
and connected to GND. Backlighting and PWM dimming of the
LEDs for the LCD display are controlled by EN13, while EN45
controls the blinking and dimming level for LED5.
(2)
where:
Ii is the LED(i) channel current;
Vi is the LED(i) channel voltage;
IIN is the supply current (rms); and
VIN is the supply voltage (rms).
If all the LED strings are equivalent, I1 = I2 = … = I5 and V1 =
V2 = … = V5 and N channels are used (N = 1, 2, 3, 4 or 5),
the equation simplifies to:
𝜂 = 𝑁
𝐼𝐿𝐸𝐷 𝑉𝐿𝐸𝐷
𝐼𝐼𝑁 𝑉𝐼𝑁
(3)
where:
ILED is the LED channel current (total output current is
N*ILED) and VLED is the LED channel voltage.
Figure 30. Schematic for Flashlight Applications
To use FAN5776 as an LED flashlight driver, as shown in
Figure 30, connect VIN to the battery voltage and add a
single-pole switch (mechanical or electrical) from EN13 and/or
EN45 pins to VIN. Pull-down resistors on the EN pins disable
the device when the switch is in a non-conducting state.
There are two LED output groups with separate control for
each group. EN13 and EN45 pins are the control/PWM for
LED1-3 and LED4-5 outputs, respectively.
© 2010 Fairchild Semiconductor Corporation
FAN5776 • Rev. 1.1.0
www.fairchildsemi.com
13
FAN5776 — Synchronous Boost and Series/Parallel 10-LED Driver
5
FAN5776 — Synchronous Boost and Series/Parallel 10-LED Driver
Physical Dimensions
0.03 C
E
2X
F
A
0.80
B
1.20
0.40
PIN A1 AREA
D
(Ø0.200)
Cu Pad
(Ø0.300)
Solder Mask
0.40
0.03 C
2X
TOP VIEW
RECOMMENDED LAND PATTERN
(NSMD PAD TYPE)
0.292±0.018
0.539
0.461
0.05 C
0.208±0.021
0.06 C
C
SEATING PLANE
D
SIDE VIEWS
0.005
0.80
Ø0.260±0.02
12X
0.40
1.20
NOTES:
A. NO JEDEC REGISTRATION APPLIES.
B. DIMENSIONS ARE IN MILLIMETERS.
D
C
B
A
0.40
C A B
(Y)±0.018
F
1 2 3
(X)±0.018
C. DIMENSIONS AND TOLERANCES PER
ASME Y14.5M, 1994.
D. DATUM C IS DEFINED BY THE SPHERICAL
CROWNS OF THE BALLS.
E. PACKAGE NOMINAL HEIGHT IS 500 MICRONS
±39 MICRONS (461-539 MICRONS).
BOTTOM VIEW
F. FOR DIMENSIONS D, E, X, AND Y SEE
PRODUCT DATASHEET.
G. DRAWING FILENAME: MKT-UC012ADrev1.
Figure 31. 12-Bump, Wafer-Level Chip-Scale Package (WLCSP) 1.42 x 1.66 x 0.50 mm, 0.40 mm Pitch
Product-Specific Dimensions
D
E
X
Y
1.660 mm
1.420 mm
0.310 mm
0.230 mm
Package drawings are provided as a service to customers considering Fairchild components. Drawings may change in any manner without
notice. Please note the revision and/or date on the drawing and contact a Fairchild Semiconductor representative to verify or obtain the most
recent revision. Package specifications do not expand the terms of Fairchild’s worldwide terms and conditions, specifically the warranty therein, which
covers Fairchild products.
Always visit Fairchild Semiconductor’s online packaging area for the most recent package drawings:
http://www.fairchildsemi.com/dwg/UC/UC012AD.pdf.
© 2010 Fairchild Semiconductor Corporation
FAN5776 • Rev. 1.1.0
www.fairchildsemi.com
14
FAN5776 — Synchronous Boost and Series/Parallel 10-LED Driver
© 2010 Fairchild Semiconductor Corporation
FAN5776 • Rev. 1.1.0
www.fairchildsemi.com
15
Mouser Electronics
Authorized Distributor
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