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LM2796
Dual-Display White LED Driver with 3/2x Switched
Capacitor Boost
LM2796 Dual-Display White LED Driver with 3/2x Switched Capacitor Boost
February 2004
General Description
The LM2796 is a charge-pump based white-LED driver that
is ideal for mobile phone display backlighting. It can drive up
to 7 LEDs in parallel with up to 20mA through each LED.
Regulated internal current sources deliver excellent current
and brightness matching in all LEDs. The LED-driver current
sources are split into two independently controlled groups.
The primary group (4 LEDs) can be used to backlight the
main phone display. The second group (3 LEDs) can be
used to backlight a secondary display or to provide other
lighting features (keypad LEDs, for example). Brightness of
the two groups can be adjusted independently with pulsewidth modulated (PWM) digital signals.
The LM2796 works off an extended Li-Ion input voltage
range (2.7V to 5.5V). Voltage boost is achieved with a highefficiency 3/2x-gain charge pump.
The LM2796 is available in National’s chip-scale 18-bump
micro SMD package.
Typical Application Circuit
Features
n Drives up to 7 LEDs with up to 20mA each
n LEDs controlled in 2 Distinct Groups, for Backlighting 2
Displays (main LCD and sub-LCD)
n Excellent Current and Brightness Matching
n High-Efficiency 3/2x Charge Pump
n Extended Li-Ion Input: 2.7V to 5.5V
n PWM Brightness Control: 100Hz - 1kHz
n 18-bump Thin Micro SMD Package:
(2.1mm x 2.4mm x 0.6mm)
Applications
n Mobile Phone Display Lighting
n Mobile Phone Keypad Lighting
n PDAs
n General LED Lighting
20093801
© 2004 National Semiconductor Corporation DS200938 www.national.com
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Connection Diagram
LM2796
Pin Description
Pin #s Pin Names Pin Descriptions
C1 V
D2 GND Ground
A3 P
A1, B2, A5, E1 C1+, C1-, C2+,
A7 EN Enable pin. Logic input. High = normal operation, Low = shutdown (charge
D6, E5, D4, E3 D1A, D2A, D3A,
C5, B4, C3 D1B, D2B, D3B LED Outputs - Group B
B6 EN-A Enable for Group-A LEDs (current outputs). Logic input.
E7 EN-B Enable for Group-B LEDs (current outputs). Logic input.
C7 I
18-Bump Thin Micro SMD Package, Large Bump
NS Package Number TLA18
IN
OUT
Input voltage. Input range: 2.7V to 5.5V.
Charge pump output. Approximately 1.5xV
Flying capacitor connections.
C2-
pump and all current sources OFF).
LED Outputs - Group A
D4A
High = Group-A LEDs ON. Low = Group A LEDs OFF.
Pulsing this pin with a PWM signal (100Hz-1kHz) can be used to dim LEDs.
High = Group-B LEDs ON. Low = Group B LEDs OFF.
Pulsing this pin with a PWM signal (100Hz-1kHz) can be used to dim LEDs.
SET
Placing a resistor (R
) between this pin and GND sets the LED current for
SET
all LEDs. LED Current = 100 x (1.25V ÷ R
IN
SET
20093802
).
Ordering Information
Order Information Package Supplied As
LM2796TL TLA18 Micro SMD 250 Units, Tape & Reel
LM2796TLX 3000 Units, Tape & Reel
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LM2796
Absolute Maximum Ratings (Notes 1, 2)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
pin voltage -0.3V to 7.1V
V
IN
EN, ENA, ENB pin voltages -0.3V to (V
+0.3V)
IN
Operating Rating (Notes 1, 2)
Input Voltage Range 2.7V to 5.5V
Junction Temperature (T
Ambient Temperature (T
(Note 5)
) Range -30˚C to +125˚C
J
) Range
A
-30˚C to +85˚C
w/ 5.6V max
Continuous Power Dissipation
Internally Limited
(Note 3)
Junction Temperature (T
) 150oC
J-MAX
Storage Temperature Range -65
Maximum Lead Temperature
o
C to +150oC
265
o
C
Thermal Properties
Juntion-to-Ambient Thermal
Resistance (θ
), (Note 6)
JA
100˚C/W
(Soldering, 10 sec.)
ESD Rating (Note 4)Human Body
Model:
2.0kV
200V
Machine Model
Electrical Characteristics (Notes 2, 7)
Limits in standard typeface and typical values apply for TJ=25oC. Limits in boldface type apply over the full operating junction
temperature range (-30˚C ≤ T
Group B LEDs not ON simultaneously (ENA = V
, and C
C
2
= 1µF. (Note 8)
POUT
≤ +85˚C) . Unless otherwise specified: VIN= 3.6V; V
J
and ENB = GND, or ENA = GND and ENB = VIN); R
IN
Symbol Parameter Condition Min Typ Max Units
≤ 4.2V, and VIN= 5.5V
IN
≤ 3.8V;
Dxx
= 8.35kΩ
≤ 5.5V;
IN
≤ 3.6V;
Dxx
= 6.25kΩ
≤ 5.5V;
IN
≤ 3.9V;
Dxx
= 12.5kΩ
≤ 3.0V;
IN
≤ 3.3V;
Dxx
= 8.35kΩ
outputs active),
DX
= 3.0V, CIN=C
OUT
= 2.2µF
= 3.0V (Note 10) 1 %
I
Dxx
I
Dxx-MATCH
Output Current Regulation
Current Matching Between Any
3.0V ≤ V
2.5V ≤ V
R
SET
3.0V ≤ V
2.5V ≤ V
R
SET
3.0V ≤ V
2.5V ≤ V
R
SET
2.7V ≤ V
2.5V ≤ V
R
SET
ENA and ENB ON (all 7 I
V
IN
V
IN
Two Group A Outputs or Group
B Outputs
I
Q
Quiescent Supply Current 2.7V ≤ VIN≤ 4.2V;
No Load Current,
EN = ON, ENA = ENB = OFF
I
SD
V
SET
I
Dxx/ISET
Shutdown Supply Current 2.7V ≤ VIN≤ 5.5V, EN = OFF 3 4.5 µA
I
Pin Voltage 2.7V ≤ VIN≤ 5.5V 1.25 V
SET
Output Current to Current Set
Ratio
R
OUT
Charge Pump Output Resistance
VIN= 3.0V 2.7 Ω
(Note 11)
V
HR
Current Source Headroom
Voltage Requirement (Note 12)
I
=95%XI
Dxx
= 8.35kΩ
R
SET
(nom) ≈ 15mA)
(I
Dxx
= 95%X I
I
Dxx
= 12.5kΩ
R
SET
(nom) ≈ 10mA)
(I
Dxx
Dxx
Dxx
(nom)
(nom)
= 3.6V; V(EN) = 2.0V; Group A and
Dxx
13.8
(-8%)
= 8.35kΩ;CIN,C1,
SET
15
16.2
(+8%)mA(%)
20
10
15
15
3.5 6 mA
100
320 mV
220
mA
mA
mA
mA
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