LM2751 Regulated 2X, 1.5X Switched Capacitor White LED Driver

LM2751
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SNVS299B – APRIL 2005 – REVISED MAY 2013
LM2751 Regulated 2X, 1.5X Switched Capacitor White LED Driver
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FEATURES
APPLICATIONS
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1
2
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Regulated Output Options: 4.5V, 5.0V
Output Voltage Regulated Within 3%
Peak Efficiency Over 90%
150mA (4.5V) or 80mA (5.0V) Output Current
Capability
Input Voltage Range: 2.8V to 5.5V
Low Input and Output Voltage Ripple
<1µA Typical Shutdown Current
Small Solution Size - NO INDUCTOR
Programmable 725kHz, 300kHz, 37kHz, or
9.5kHz Switching Frequencies
10-pin SON No-Pullback Package: 3mm × 3mm
× 0.8mm
White LED Display Backlights
White LED Keypad Backlights
General Purpose 2×, 1.5× Regulated Charge
Pump
DESCRIPTION
The LM2751 is a constant frequency switched
capacitor charge pump with regulated output voltage
options of 4.5V, and 5.0V. Over the input voltage
range of 2.8V to 5.5V the LM2751 provides up to
150mA of output current and requires only four lowcost ceramic capacitors.
Typical Application Circuit
VOUT = 4.5V, or 5.0V
VIN = 2.8V - 5.5V
3
CIN
2
2.2 µF
C1
VIN
VOUT
1
C1+
2.2 µF
9
10
C 1C 2+
LM2751
EN
CS1
Capacitors:
C 2-
DX
R
R
4
1 µF
7
D1
6
CS0
C2
COUT
1 µF
5
GND
8
1 µF - TDK C1608X7R1A105K
2.2 µF - TDK C2012X5R1A225K
LM2751 2x/1.5x Efficiency vs.
2x Charge Pump Efficiency
100
EFFICIENCY (%)
90
LM2751 2x, 1.5x Pump
VOUT = 4.5V
VOUT = 5.0V
80
70
60
VOUT = 5.0V
VOUT = 4.5V
50
Typical 2x Only Pump
40
2.7
3.0
3.3
3.6
3.9
4.2
INPUT VOLTAGE (V)
1
2
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2005–2013, Texas Instruments Incorporated
LM2751
SNVS299B – APRIL 2005 – REVISED MAY 2013
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DESCRIPTION (CONTINUED)
The LM2751 provides excellent efficiency without the use of an inductor by operating the charge pump in a gain
of 3/2 or 2. The proper gain for maintaining regulation is chosen so that efficiency is maximized over the input
voltage range.
LM2751 uses constant frequency pre-regulation to minimize conducted noise on the input and provide a
predictable switching frequency. The switching frequency is programmable to 725kHz, 300kHz, 37kHz, or
9.5kHz.
LM2751 is available in a 10-pin SON No-Pullback Package.
Connection Diagram
VOUT
1
10
C2+
C2+
10
1
VOUT
C1+
2
9
C1-
C1-
9
2
C1+
VIN
3
8
GND
GND
8
3
VIN
CS0
4
7
C2-
C2-
7
4
CS0
CS1
5
6
EN
EN
6
5
CS1
Die-Attach Pad: GND
Die-Attach Pad: GND
Top View
Bottom View
Figure 1. 10-pin SON No Pullback Package (3mm × 3mm × 0.8mm)
See Package Number DSC0010A
PIN DESCRIPTIONS
Pin #
Name
Description
1
VOUT
2
C1+
Flying Capacitor C1 Connection.
3
VIN
Input Supply Range: 2.8V to 5.5V.
4
CS0
Frequency Select Input 0.
5
CS1
Frequency Select Input 1.
6
EN
Enable Pin Logic Input.
7
C2−
Flying Capacitor C2 Connection.
8
GND
9
C1−
Flying Capacitor C1 Connection.
10
C2+
Flying Capacitor C2 Connection.
Pre-Regulated Output.
Ground.
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
2
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ABSOLUTE MAXIMUM RATINGS (1) (2) (3)
−0.3V to 6.0V
VIN Pin
−0.3V to (VIN+0.3)
w/ 6.0V max
EN, CS0, CS1 Pins
Continuous Power Dissipation (4)
Internally Limited
Junction Temperature (TJ-MAX-ABS)
150°C
−65°C to 150°C
Storage Temperature Range
Maximum Lead Temperature
ESD Rating
(5)
(Soldering, 10sec.)
265°C
Human-body model
2kV
Machine model
(1)
(2)
(3)
(4)
(5)
200V
Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under
which operation of the device is specified. Operating Ratings do not imply ensured performance limits. For specified performance limits
and associated test conditions, see the Electrical Characteristics tables.
All voltages are with respect to the potential at the GND pin.
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ=150°C (typ.) and
disengages at TJ=140°C (typ.).
The Human body model is a 100 pF capacitor discharged through a 1.5kΩ resistor into each pin. The machine model is a 200pF
capacitor discharged directly into each pin (MIL-STD-883 3015.7).
OPERATING RATINGS (1) (2)
Input Voltage Range
2.8V to 5.5V
EN, CS0, CS1 Input Voltage Range
0V to VIN
Junction Temperature (TJ) Range
-40°C to 115°C
Ambient Temperature (TA) Range (3)
-40°C to 85°C
Recommended Maximum Load Current
Version B
Version A
(1)
(2)
(3)
Freq. = 725kHz
150mA
Freq. = 300kHz
120mA
Freq. = 37kHz
40mA
Freq. = 9.5kHz
10mA
Freq. = 725kHz
80mA
Freq. = 300kHz
60mA
Freq. = 37kHz
16mA
Freq. = 9.5kHz
4mA
Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under
which operation of the device is specified. Operating Ratings do not imply ensured performance limits. For specified performance limits
and associated test conditions, see the Electrical Characteristics tables.
All voltages are with respect to the potential at the GND pin.
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 operation junction temperature (TJ-MAX-OP =
115ºC), 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 (θJA), as given by the following equation:
TA-MAX = TJ-MAX-OP - (θJA × PD-MAX).
THERMAL PROPERTIES
Junction-to-Ambient Thermal
Resistance, 10-pin SON
(1)
Package (θJA) (1)
55°C/W
Junction-to-ambient thermal resistance (θJA) is taken from a thermal modeling result, performed under the conditions and guidelines set
forth in the JEDEC standard JESD51-7. The test board is a 4 layer FR-4 board measuring 102mm x 76mm x 1.6mm with a 2 x 1 array
of thermal vias. The ground plane on the board is 50mm x 50mm. Thickness of copper layers are 36µm/18µm
/18µm/36µm(1.5oz/1oz/1oz/1.5oz). Ambient temperature in simulation is 22ºC, still air. Power dissipation is 1W. The value of θJA of the
LM2751 in 10-pin SON could fall in a range as wide as 50ºC/W to 150ºC/W (if not wider), depending on PWB material, layout, and
environmental conditions. In applications where high maximum power dissipation exists (high VIN, high IOUT), special care must be paid
to thermal dissipation issues. For more information on these topics, see the TI AN-1187 Application Report (SNOA401) and the Power
Efficiency and Power Dissipation section of this datasheet.
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LM2751
SNVS299B – APRIL 2005 – REVISED MAY 2013
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ELECTRICAL CHARACTERISTICS (1) (2)
Limits in standard typeface are for TA = 25ºC. Limits in boldface type apply over the full operating ambient temperature range
(-40°C ≤ TA ≤ +85°C) . Unless otherwise noted, specifications apply to the LM2751 Typical Application Circuit (pg. 1) with: VIN
= 3.6V, V(EN) = VIN, CS0 = CS1 = VIN, C1 = C2 = 1.0µF, CIN = COUT = 2.2µF (3).
Symbol
VOUT
Parameter
Output Voltage
Conditions
Version A, 2.8V ≤ VIN ≤ 5.5V,
Freq. = 300kHz, 725kHz, TA = 25°C
IOUT = 0 to 60mA
Min
Typ
Max
Units
4.850
(-3%)
5.0
5.150
(+3%)
V
Version A, 2.8V ≤ VIN ≤ 5.5V,
Freq. = 300kHz, IOUT = 0 to 60mA
Freq. = 725kHz, IOUT = 0 to 80mA
4.775
(-4.5%)
Version B, 2.8V ≤ VIN ≤ 5.5V,
Freq. = 300kHz, 725kHz, TA = 25°C
IOUT = 0 to 120mA
4.343
(-3.5%)
Version B, 2.8V ≤ VIN ≤ 5.5V,
Freq. = 300kHz, IOUT = 0 to 120mA
Freq. = 725kHz, IOUT = 0 to 150mA
4.275
(-5%)
5.225
(+4.5%)
4.5
4.658
(+3.5%)
4.725
(+5%)
VR
Output Ripple
2.8V ≤ VIN ≤ 5.5V
IOUT = 60mA
IQ
Quiescent Current
Freq. = 9.5kHz, IOUT = 0mA, VIN = 3.7V
425
600
Freq. = 37kHz, IOUT = 0mA, VIN = 3.7V
450
640
ISD
E
f
SW
Shutdown Supply Current
Efficiency
Switching Frequency
8
mV
Freq. = 300kHz, IOUT = 0mA, VIN = 3.7V
700
900
Freq. = 725kHz, IOUT = 0mA, VIN = 3.7V
1000
1500
V(EN) = 0V
0.77
1.3
V(EN) = 0V, TA = 85°C
1.0
IOUT = 80mA (Version A, 5.0V)
Freq. = 300kHz, 725kHz
92
IOUT = 150mA (Version B, 4.5V)
Freq. = 300kHz, 725kHz
83
µA
µA
%
CS0 = High, CS1 = Low
2.8V ≤ VIN ≤ 5.5V
6.7
(−30%)
9.5
12.3
(+30%)
CS0 = Low, CS1 = Low
2.8V ≤ VIN ≤ 5.5V
26
(−30%)
37
48
(+30%)
CS0 = Low, CS1 = High
2.8V ≤ VIN ≤ 5.5V
210
(−30%)
300
390
(+30%)
CS0 = High, CS1 = High
2.8V ≤ VIN ≤ 5.5V
508
(−30%)
725
942
(+30%)
kHz
VIH
Logic Input High
Input Pins: EN, CS0, CS1
2.8V ≤ VIN ≤ 5.5V
1.00
VIN
V
VIL
Logic Input Low
Input Pins: EN, CS0, CS1
2.8V ≤ VIN ≤ 5.5V
0
.30
V
IIH
Logic Input High Current
Input Pins: CS0, CS1
V(CSx) = 1.8V
10
nA
Input Pin: EN
V(EN) = 1.8V (4)
2
µA
10
nA
3.50
3.58
V
IIL
Logic Input Low Current
Input Pins: EN, CS0, CS1
V(EN, CSx) = 0V
VG
Gain Transition Voltage
(Version A, B)
1.5X to 2X
2X to 1.5X
ISC
Short Circuit Output
Current
Hysteresis
(1)
(2)
(3)
(4)
4
40
VOUT = 0V
80
250
150
mV
mA
All voltages are with respect to the potential at the GND pin.
Min and Max limits are specified by design, test, or statistical analysis. Typical numbers are not ensured, but represent the most likely
norm.
CIN, COUT, C1, and C2: Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics.
EN Logic Input High Current (IIH) is due to a 1MΩ(typ.) pull-down resistor connected internally between the EN pin and GND.
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ELECTRICAL CHARACTERISTICS(1)(2) (continued)
Limits in standard typeface are for TA = 25ºC. Limits in boldface type apply over the full operating ambient temperature range
(-40°C ≤ TA ≤ +85°C) . Unless otherwise noted, specifications apply to the LM2751 Typical Application Circuit (pg. 1) with: VIN
= 3.6V, V(EN) = VIN, CS0 = CS1 = VIN, C1 = C2 = 1.0µF, CIN = COUT = 2.2µF (3).
Symbol
tON
(5)
Parameter
VOUT Turn-On Time
Conditions
(5)
Min
Typ
Max
Units
300
µs
Turn-on time is measured from when the EN signal is pulled high until the output voltage on VOUT crosses 90% of its final value.
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LM2751
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BLOCK DIAGRAM
LM2751
VIN
C1+
GAIN
CONTROL
1.2V Ref.
SWITCH
CONTROL
SWITCH
ARRAY
CS0
G= 2 ,
C13
2
C2+
FREQ. CTRL
CS1
C2-
725 kHz
OSC
Divider
(Div 16,
Div 8)
300 kHz
VOUT
Short-Circuit
Protection
Thermal Shutdown
OSCILLATOR
EN
EN
6
Enable /
Shutdown
Control
1.2V
Ref.
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Soft-Start
Ramp
GND
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TYPICAL PERFORMANCE CHARACTERISTICS
Unless otherwise specified: TA = 25°C, VIN = 3.6V, CS0 = CS1 = VIN, V(EN) = VIN, CIN = COUT = 2.2µF, C1 = C2 = 1µF.
Output Voltage
vs.
Output Current, Version A (5V), 300kHz
Output Voltage
vs.
Output Current, Version B (4.5V), 300kHz
4.60
VIN = 4.2V
5.08
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
5.10
VIN = 5.5V
VIN = 3.3V
5.05
5.03
4.58
VIN = 5.5V
VIN = 4.2V
4.56
VIN = 2.8V
4.54
VIN = 3.6V
4.52
VIN = 3.6V
VIN = 3.3V
VIN = 2.8V
4.50
5.00
0
10
20
30
40
50
60
0 13 26 39 52 65 78 91 104 117 130
70
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
Figure 2.
Figure 3.
Output Voltage
vs.
Output Current, Version A (5V), 725kHz
Output Voltage
vs.
Output Current, Version B (4.5V), 725kHz
4.60
VIN = 5.5V
5.06
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
5.08
VIN = 4.2V
5.03
5.01
4.57
VIN = 5.5V
VIN = 4.2V
4.54
4.51
VIN = 3.3V
VIN = 3.6V
4.48
VIN = 2.8V
VIN = 3.6V
VIN = 2.8V
VIN = 3.3V
4.45
4.98
0
15
30
45
60
75
0
90
20
1.70
40
60
80
100 120 140 160
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
Figure 4.
Figure 5.
Input Current
vs.
Input Voltage, Version A (5V)
Input Current
vs.
Input Voltage, Version B (4.5V)
1.5
FSW = 725 kHz
IOUT = 0
1.50
FSW = 725 kHz
IOUT = 0
1.3
TA = 25°C
TA = 25°C
IQ (mA)
IQ (mA)
1.30
1.10
FSW = 300 kHz
1.1
0.9
0.90
0.7
0.70
FSW = 300 kHz
0.5
0.50
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
INPUT VOLTAGE (V)
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
INPUT VOLTAGE (V)
Figure 6.
Figure 7.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Unless otherwise specified: TA = 25°C, VIN = 3.6V, CS0 = CS1 = VIN, V(EN) = VIN, CIN = COUT = 2.2µF, C1 = C2 = 1µF.
Output Voltage
vs.
Input Voltage, Version A (5V), 300kHz
Output Voltage
vs.
Input Voltage, Version B (4.5V), 300kHz
5.09
4.63
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
IOUT = 0 mA
5.07
IOUT = 20 mA
5.04
IOUT = 60 mA
5.02
4.60
IOUT = 0 mA
4.57
IOUT = 40 mA
4.54
IOUT = 120 mA
4.51
IOUT = 70 mA
IOUT = 80 mA
4.99
4.48
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
2.7
3.1
INPUT VOLTAGE (V)
3.5
3.9
4.3
4.7
5.1
5.5
INPUT VOLTAGE (V)
Figure 8.
Figure 9.
Output Voltage
vs.
Input Voltage, Version A (5V), 725kHz
Output Voltage
vs.
Input Voltage, Version B (4.5V), 725kHz
5.09
4.60
5.06
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
IOUT = 0 mA
IOUT = 0 mA
IOUT = 20 mA
5.03
IOUT = 80 mA
5.00
4.57
4.54
IOUT = 40 mA
IOUT = 120 mA
4.51
IOUT = 152 mA
4.48
IOUT = 60 mA
4.97
4.45
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
2.7
3.1
4.3
4.7
5.1
Figure 11.
Efficiency
vs.
Input Voltage, Version A (5V)
Efficiency
vs.
Input Voltage, Version B (4.5V)
100
90
90
80
70
60
50
5.5
80
70
60
50
3.1
3.5
3.9
4.3
4.7
5.1
5.5
INPUT VOLTAGE (V)
40
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
INPUT VOLTAGE (V)
Figure 12.
8
3.9
Figure 10.
100
40
2.7
3.5
INPUT VOLTAGE (V)
EFFICIENCY (%)
EFFICIENCY (%)
INPUT VOLTAGE (V)
Figure 13.
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TYPICAL PERFORMANCE CHARACTERISTICS (continued)
Unless otherwise specified: TA = 25°C, VIN = 3.6V, CS0 = CS1 = VIN, V(EN) = VIN, CIN = COUT = 2.2µF, C1 = C2 = 1µF.
Output Voltage Ripple
vs. Input Voltage Version B (4.5V), Load = 120mA
OUTPUT VOLTAGE RIPPLE (mV)
22
Output Voltage Ripple, Version B (4.5V)
CIN = 1.0 F
COUT: 2.2 F
Capacitance,
300 kHz
18
13
COUT: 2.2 F
Capacitance,
725 kHz
9
COUT: 10 F
Capacitance,
725 kHz
COUT: 10 F
Capacitance,
300 kHz
4
0
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
INPUT VOLTAGE (V)
Figure 14.
VIN = 3.6V, Load = 150mA
CH1: VOUT; Scale: 10mV/Div, AC Coupled
Time scale: 400ns/Div
Figure 15.
Line Step Response, Version B (4.5V)
VIN = 3.2V - 4.2V Step, Load = 150mA
CH1 (top): VIN; Scale: 1V/Div, DC Coupled
CH2: VOUT; Scale: 50mV/Div, AC Coupled
Time scale: 200µs/Div
Figure 16.
VIN = 3.6V, Load = 20mA - 150mA Step
CH1 (top): VOUT; Scale: 50mV/Div, AC Coupled
CH2: Output Current; Scale: 50mA/Div
Time scale: 200µs/Div
Figure 17.
Start-up Behavior, Version A (5V), Load = 80mA
CH1: EN pin; Scale: 2V/Div
CH2: VOUT; Scale: 2V/Div
Time scale: 100µs/Div
Load Step Response, Version B (4.5V)
Start-up Behavior, Version B (4.5V), Load = 150mA
CH1: EN pin; Scale: 2V/Div
CH2: VOUT; Scale: 2V/Div
Time scale: 100µs/Div
Figure 18.
Figure 19.
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APPLICATION INFORMATION
CIRCUIT DESCRIPTION
The LM2751 is a Switched Capacitor Convertor with gains of 2x and 1.5x. It is capable of continuously supplying
up to 150mA at 4.5V or up to 80mA at 5V depending on the output voltage option. The LM2751's fixed frequency
pre-regulation maintains the output voltage to within 3% (typ.), making it well suited for driving White LEDs.
There are also four user programmable switching frequencies to reduce the quiescent current consumption at
light loads.
Aside from powering LEDs, the LM2751 is suitable for driving other devices with power requirements up to
150mA. The LM2751 operates over the extended Li-Ion battery range from 2.8V to 5.5V. The LM2751 limits
output current to 250mA (typ.) during an output short circuit condition. LED brightness is controlled by applying a
PWM (Pulse Width Modulation) signal to the Enable pin (EN). See PWM BRIGHTNESS CONTROL.
SOFT START
Soft Start is engaged when the device is taken out of Shutdown mode (EN = logic HIGH) or when voltage is
supplied simultaneously to the VIN and EN pins. During Soft Start, the voltage on VOUT will ramp up in proportion
to the rate that the reference voltage is being ramped up. The output voltage is programmed to rise from 0V to
the regulated output voltage level (4.5V or 5V) in 300µs (typ.).
ENABLE MODE
The Enable logic pin (EN) disables the part and reduces the quiescent current to 0.77µA (typ.). The LM2751 has
an active-high enable pin (LOW = shut down, HIGH = operating) which can be driven with a low-voltage CMOS
logic signal (1.5V logic, 1.8V logic, etc). There is an internal 1MΩ pull-down resistor between the EN and GND
pins of the LM2751.
FREQUENCY MODE SELECT
The LM2751 switching frequency is user programmable via two logic input pins, CS0 and CS1. Both logic input
pins have active-high logic (LOW = un-selected, HIGH = selected) and can be driven with a low-voltage CMOS
logic signal (1.5V logic, 1.8V logic, etc). There are no internal pull-down or pull-up resistors between the CSx and
GND pins of the LM2751. The CSO and CS1 can be controlled independently or with the same logic signal.
The selectable switching frequencies are 9.5kHz, 37kHz, 300kHz, 725kHz. The switching frequency is
programmed according to Table 1.
Table 1. Frequency Modes
CS0
CS1
Frequency
0
0
37kHz
0
1
300kHz
1
0
9.5kHz
1
1
725kHz
VOUT REGULATION
The LM2751 uses pre-regulation to regulate the output voltage to 4.5V or 5.0V depending on the voltage option.
Pre-regulation uses the voltage present at VOUT to limit the gate drive of the switched capacitor charge pump.
This regulation is done before the voltage is gained up by the charge pump, giving rise to the term "preregulation". Pre-regulation helps to reduce input current noise and large input current spikes normally associated
with switched capacitor charge pumps.
The LM2751 switched capacitor charge pump has gains of 2x and 1.5x. When the input voltage to the device is
greater than 3.58V (typ.), the LM2751 operates in a gain of 1.5x. When the input voltage falls below 3.5V (typ.),
the device switches to a gain of 2x.
10
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OUTPUT VOLTAGE RIPPLE
The primary contributor in keeping the output voltage ripple of the LM2751 low is its switching topology. The
output capacitance, input voltage, switching frequency and output current also play a significant part in
determining the output voltage ripple. Due to the complexity of the LM2751 operation, providing equations or
models to approximate the magnitude of the ripple cannot be easily accomplished. However, the following
general statements can be made.
The LM2751 has very low output ripple when compared to typical boost regulators due to its double-pump
topology, where charge is continually supplied to the output during both 2x and 1.5x modes. Combined with fixed
frequency operation modes, double-pumping allows for the use of a very small, low value ceramic capacitor on
the output node while still achieving minimal output ripple. Increasing the capacitance by adding a higher value
capacitor or placing multiple capacitors in parallel can further reduce the ripple magnitude.
CAPACITOR SELECTION
The LM2751 requires 4 external capacitors for proper operation. Surface-mount multi-layer ceramic capacitors
are recommended. These capacitors are small, inexpensive and have very low equivalent series resistance
(ESR, ≤15mΩ typ.). Tantalum capacitors, OS-CON capacitors, and aluminum electrolytic capacitors are generally
not recommended for use with the LM2751 due to their high ESR, as compared to ceramic capacitors.
For most applications, ceramic capacitors with X7R or X5R temperature characteristic are preferred for use with
the LM2751. These capacitors have tight capacitance tolerance (as good as ±10%), hold their value over
temperature (X7R: ±15% over −55°C to 125°C; X5R: ±15% over −55°C to 85°C), and typically have little voltage
coefficient when compared to other types of capacitors. However selecting a capacitor with a voltage rating much
higher than the voltage it will be subjected to, will ensure that the capacitance will stay closer to the capacitor's
nominal value. Capacitors with Y5V or Z5U temperature characteristic are generally not recommended for use
with the LM2751. Capacitors with these temperature characteristics typically have wide capacitance tolerance
(+80%, −20%), vary significantly over temperature (Y5V: +22%, −82% over −30°C to +85°C range; Z5U: +22%,
−56% over +10°C to +85°C range), and have poor voltage coefficients. Under some conditions, a nominal 1µF
Y5V or Z5U capacitor could have a capacitance of only 0.1µF. Such detrimental deviation is likely to cause Y5V
and Z5U capacitors to fail to meet the minimum capacitance requirements of the LM2751.
The voltage rating of the output capacitor should be 10V or more. All other capacitors should have a voltage
rating at or above the maximum input voltage of the application.
DRIVING WHITE LEDS
The desired LED current is set by placing a resistor (R) in series with each LED, and is determined by the
equation:
ILED = (VOUT - VLED) ÷R
(1)
In the equation above, ILED is the current that flows through a particular LED, and VLED is the forward voltage of
the LED at the given current. The output voltage (VOUT) of the LM2751 is tightly regulated to 4.5V or 5V
depending on the output voltage option. However, LED forward voltage varies from LED to LED, and LED current
will vary accordingly. Mismatch of LED currents will result in brightness mismatch from one LED to the next.
Therefore it is suggested that LED groups with tightly controlled I-V characteristics ("Binned" LEDs) be used.
LEDs with looser tolerance can be used in applications where brightness matching is not critical, such as in
keypad or general backlighting. The typical and maximum diode forward voltage depends highly on the
manufacturer and their technology.
PWM BRIGHTNESS CONTROL
Perceived LED brightness can be adjusted using a PWM control signal on the Enable pin of the LM2751, to turn
the voltage output ON and OFF at a rate faster than perceptible by the eye. When this is done, the total
brightness perceived is proportional to the duty cycle (D) of the PWM signal (D = the percentage of time that the
LED is on in every PWM cycle). A simple example: if the LEDs are driven at 15mA each with a PWM signal that
has a 50% duty cycle, perceived LED brightness will be about half as bright as compared to when the LEDs are
driven continuously with 15mA.
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LM2751
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For linear brightness control over the full duty cycle adjustment range, the PWM frequency (f) should be limited
to accommodate the turn-on time (typ. TON = 300µs) of the device.
D × (1/f) > TON
fMAX = DMIN ÷ TON
(2)
(3)
The minimum recommended PWM frequency is 100Hz. Frequencies below this may be visibly noticeable as
flicker or blinking. The maximum recommended PWM frequency is 1kHz. Frequencies above this may cause
noise in the audible range.
THERMAL PROTECTION
When the junction temperature exceeds 150°C (typ.), internal thermal protection circuitry disables the device.
This feature protects the LM2751 from damage due to excessive power dissipation. The device will recover and
operate normally when the junction temperature falls below 140°C (typ.). It is important to have good thermal
conduction with a proper layout to reduce thermal resistance.
POWER EFFICIENCY
Charge-Pump efficiency is derived in the following two ideal equations (supply current and other losses are
neglected for simplicity):
IIN = G x IOUT
E = (VOUT x IOUT) ÷ (VIN x IIN) = VOUT ÷ (G x VIN)
(4)
(5)
In the equations, G represents the charge pump gain. Efficiency is at its highest as G x VIN approaches VOUT.
Refer to the efficiency graph in the Typical Performance Characteristics for the detailed efficiency data.
POWER DISSIPATION
The power dissipation (PDISSIPATION) and junction temperature (TJ) can be approximated with the equations
below. PIN is the product of the input current and input voltage, POUT is the power consumed by the load
connected to the output, TAis the ambient temperature, and θJA is the junction-to-ambient thermal resistance for
the 10-pin SON package. VIN is the input voltage to the LM2751, VVOUT is the voltage at the output of the device,
and IOUT is the total current supplied to the load connected to VOUT.
PDISSIPATION = PIN - POUT
= (VIN × IIN) − (VVOUT × IOUT)
TJ = TA + (PDISSIPATION × θJA)
(6)
(7)
(8)
The junction temperature rating takes precedence over the ambient temperature rating. The LM2751 may be
operated outside the ambient temperature rating, so long as the junction temperature of the device does not
exceed the maximum operating rating of 115°C. The maximum ambient temperature rating must be derated in
applications where high power dissipation and/or poor thermal resistance causes the junction temperature to
exceed 115°C.
12
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SNVS299B – APRIL 2005 – REVISED MAY 2013
REVISION HISTORY
Changes from Revision A (May 2013) to Revision B
•
Page
Changed layout of National Data Sheet to TI format .......................................................................................................... 12
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PACKAGE OPTION ADDENDUM
www.ti.com
11-Sep-2016
PACKAGING INFORMATION
Orderable Device
Status
(1)
LM2751SD-B/NOPB
ACTIVE
Package Type Package Pins Package
Drawing
Qty
WSON
DSC
10
1000
Eco Plan
Lead/Ball Finish
MSL Peak Temp
(2)
(6)
(3)
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
Op Temp (°C)
Device Marking
(4/5)
-40 to 85
L146B
(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
www.ti.com
11-Sep-2016
Addendum-Page 2
PACKAGE MATERIALS INFORMATION
www.ti.com
10-Aug-2016
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
LM2751SD-B/NOPB
Package Package Pins
Type Drawing
WSON
DSC
10
SPQ
Reel
Reel
A0
Diameter Width (mm)
(mm) W1 (mm)
1000
178.0
12.4
Pack Materials-Page 1
3.3
B0
(mm)
K0
(mm)
P1
(mm)
3.3
1.0
8.0
W
Pin1
(mm) Quadrant
12.0
Q1
PACKAGE MATERIALS INFORMATION
www.ti.com
10-Aug-2016
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
LM2751SD-B/NOPB
WSON
DSC
10
1000
210.0
185.0
35.0
Pack Materials-Page 2
MECHANICAL DATA
DSC0010A
SDA10A (Rev A)
www.ti.com
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