a8435 Allegro MicroSystems, Inc., a8435 Datasheet - Page 8

• Manufacturer Part Number: a8435
• Description: High Efficiency Charge Pump White Led Driver
• Manufacturer: Allegro MicroSystems, Inc.

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
longer than t
A8435
Figure 3. Single-Wire Serial Dimming Control, at pin EN1; CTRL = LOW, EN2 = LOW.
I ILED
EN1
SHDN
X
SHDN
(2 ms typical) in order to enter shutdown mode.
0
t
HI(Init)
100%
t
SS
1
90%
2
80%
High Efficiency Charge Pump White LED Driver
3
70%
4
60%
5
50%
t
LO
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.
6
40%
7
30% 20%
t
HI
8
9
10%
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
10
5%
11
100% 90%
t
SHDN
SHDN
8