LTC3524

7

3524f

LCD BIAS PIN FUNCTIONS

FBN (Pin 13): Feedback Pin for the VN Charge-Pump

Output. Reference voltage is 1.0V. Connect the resistive

trace area.

VN

RV

R

See Block Diagram

OUT

=

−−

()

+

61

5

1(

)

FBH (Pin 14): Feedback Pin for the VH Charge-Pump

Output. Reference voltage is 1.225V. Connect resistive

divider tap here with minimum trace area.

VH

R

R

See Block Diagram

=+

⎛

⎝⎜

⎞

⎠⎟

1 225 1

3

4

.(

)

VH (Pin 15): Charge Pump Quadrupler Output. This output

up to 2mA to a load. VH should be bypassed to GND with

a 0.47μF X5R type ceramic capacitor. Connect V2x to

Charge Pump Quadrupler Flying Capacitor

Positive Node. The charge pump quadrupler (4X) flying

50% duty cycle while the charge pump is operating. Use

a 0.1μF X5R type ceramic capacitor for best results.

Charge Pump Quadrupler (4X) Flying Ca-

between GND and V2x at an approximate 50% duty cycle

while the charge pump is operating. Use a 0.1μF X5R type

ceramic capacitor for best results.

WHITE LED DRIVER PIN FUNCTIONS

LED2 (Pin 18): Output for Second LED String. Connect

up to five white LEDs between LED2 (anode) and GND

(cathode). For best current matching and efficiency use

the same number of white LEDs in both strings.

LED1 (Pin 19): Output for First LED String.

VLED (Pin 20): Output of the LED Switcher. Bypass VLED

with a low ESR, ESL ceramic capacitor (X5R type) of at

least 1μF. Keep PCB trace lengths as short and wide as

possible to minimize EMI and voltage overshoot.

SW2 (Pin 21): White LED Boost Switch. Connect a 3.3-

of the internal NPN power switch. Connect an external

Schottky diode between SW2 and VLED. Keep PCB trace

lengths as short and wide as possible to minimize EMI

and voltage overshoot.

ELED2 (Pin 22): Enable and PWM Dimming Control Input

for the LED2 String. The LED2 string is disabled when this

pin is grounded. Digital dimming can be implemented

by driving the ELED2 pin between 0V and >1.2V at low

frequency (ie., 500Hz). Driving ELCD, ELED1, and ELED2

low initiates shutdown mode which disables all IC func-

tions and reduces quiescent current from the battery to

less than 2μA.

PROG (Pin 23): A single resistor (RPROG) between

PROG and GND sets the current in the LED strings. LED

current in mA is programmed by:

ILED

ILED

R

mA

PROG

12

==

×

⎛

⎝⎜

⎞

⎠⎟

A 100K resistor programs 20mA in each string. Analog

dimming can be implemented by connecting a second

resistor between PROG and a control voltage.

ELED1 (Pin 24): Enable and Pulse Dimming Control Input

for the LED1 String. For applications with five or fewer

LEDs, better efficiency is achieved by operating a single

LED string. For example, ELED1 = 1, ELED2 = 0, LED2 left

open circuit and the LED string connected to LED1.