High Efficiency Charge Pump White LED Driver

A8435

8

Allegro MicroSystems, Inc.

115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (508) 853-5000

www.allegromicro.com

When changing from one specific brightness level to another, the

user may not want to keep the existing brightness level stored

in memory. A simpler method is to program a shutdown and

re-enable, followed by an appropriate number of pulses (from

100%) to reach the target brightness level. The total “LED off”

time during shutdown, re-enable, and brightness programming

can be kept sufficiently short such that no delay is discernable to

the eye.

Shutdown

If the CTRL pin is unconnected or HIGH, the device enters the

shutdown mode when EN1 and EN2 are pulled LOW. When

configured to have a serial pulse dimming control (the CTRL pin

is grounded), the EN1 and the EN2 pins must be pulled LOW for

The output is high impedance after shutdown.

Disabling Unused LEDs

If any WLED is not used, connect the corresponding pin to either

VIN or VOUT to disable it. Never leave open any unused WLED

pin. LED pins will sink 30 μA typical when connected to VIN or

VOUT and the IC is enabled.

LED3 must always be selected. For example, to drive 2 LEDs,

select LED3 and one of either LED1, LED2, or LED4.

Component Selection

Ceramic capacitors with X5R or X7R dielectric are recommended

for the input capacitor, CIN, the output capacitor, COUT, and the

charge pump capacitors, C1 and C2.

SHDN

EN1

0

100%

90% 80% 70%

60%

50%

40%

30% 20%

10%

5%

100% 90%

SHDN

1

234

5

6

78

9

10

11

Figure 3. Single-Wire Serial Dimming Control, at pin EN1; CTRL = LOW, EN2 = LOW.