National Semiconductor LM2796 Technical data

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

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

www.national.com 2

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

www.national.com3