a8434 Allegro MicroSystems, Inc., a8434 Datasheet - Page 9

• Manufacturer Part Number: a8434
• Description: 6-channel High Efficiency Charge Pump White Led Driver
• Manufacturer: Allegro MicroSystems, Inc.

A8434
Sub Display LED5 and LED6 Operation. The sub display
backlight LEDs (LED5 and LED6) brightness and on/off can
be controlled using digital input at the ENS pin. The ENS pin
accepts one-wire serial pulse input to enable the A8434 and to set
up to 11 dimming levels, from 100% down to 5%.
When ENS is initially pulled up from shutdown, after a soft-start,
the current for the backlight LEDs is programmed to 100% of
the setting current, which is determined by the current through
the ISET pin. Each subsequent pulse reduces the LED current
by 10%, and the 10
pulse restores 100% (full) brightness. Figure 5 shows the timing
diagram for ENS control.
Simultaneous Dimming of All 6 LEDs
For larger displays 6 LEDs can be grouped together. The LEDs
LED1 through LED6 can be dimmed simultaneously by con-
necting ENM and ENS together and applying serial pulses for
dimming, as shown in figure 1.
Absolute Level Operation Some applications require dimming
to a specific level, regardless of the present level of dimming.
Symbol
th
C1
C2
C3
pulse reduces the current by 5%. The next
t
Figure 6. Absolute Dimming Level Setting. With ENM pulled low longer the t
pulsing the corresponding ENx pin sets an absolute target level.
Parameter
V
V
I
time
OUT
ENM
OUT
Units/Division
2.00 V
2.00 V
0.5 ms
50 mA
6-Channel High Efficiency Charge Pump
C2
C3
C1
100%
For example, if the IC should dim to 30%, this can be done with
7 steps, as shown in figure 5, irrespective of the dimming level
in effect. This can be achieved by pulling corresponding ENx
pin low for time greater than t
shown in figure 5 (7 for 30% dimming). If the pulses are applied
within 2-3 ms, the display flicker is not visible. The procedure is
shown in figure 6.
Shutdown
When the ENM or ENS pin is pulled low for 0.5 ms or longer, the
corresponding display channels are shut off and dimming is reset
to 100% upon the next ENM or ENS going high edge. When both
ENM and ENS are pulled low for 0.5 ms or longer, the A8434
enters the shutdown mode.
Short Circuit Protection
The A8434 is protected against short circuits on the output. When
V
mode. The A8434 resumes normal operation when the short
circuit is removed.
ENx pulled low
OUT
is externally pulled below 1.2 V, the IC enters short circuit
∆t > t
SHDN
I
SET
t
counter resets
115 Northeast Cutoff, Box 15036
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 [phone]
www.allegromicro.com
White LED Driver
SHDN
SHDN
Rapid pulse pattern
,
and then applying pulses as
30%
V
V
I
ENM
OUT
OUT
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