a8530 Allegro MicroSystems, Inc., a8530 Datasheet - Page 8

• Manufacturer Part Number: a8530
• Description: Ultracompact 6-channel Backlight And Flash/torch White Led Driver
• Manufacturer: Allegro MicroSystems, Inc.

A8530
Setting LED Current
Use the following formula to set the display backlight LED full
current (100%) using RSET on LED1 through LED4. The maxi-
mum current through one LED should not exceed 30 mA:
where R
The default flash/torch current on LED5 and LED6 is set inter-
nally to 100 mA per channel. When both the display backlight
and the flash/torch LEDs are on, the maximum current output
from LED1 through LED4 is 30 mA per channel. The output cur-
rent of the flash/torch LEDs (LED5 and LED6) can be adjusted
by serial dimming at the ENF pin within 1 ms after ENF is pulled
high.
Transitions Between 1× and 1.5× or 2× Modes
The A8530 adaptively selects operating mode. When V
ficiently high to maintain V
ENM (LED1-4) or
ENF (LED5-6)
Figure 5. Mode change transitions
95
90
85
80
75
70
65
60
55
I ILED
I ILED
2.7
Figure 6. Single-Wire Serial Dimming Control; at pins ENF and ENM.
SET
(1-4)
(5-6)
R
SET
is in Ω and I
or
3.1
= 0.6 V × 220 / I
SHDN
0
3.5
LEDx
t
HI(Init)
100%
LEDx
3.9
t
SS
in amperes.
LEDx
V IN (V)
> 150 mV, the A8350 operates
4.3
1
90%
2
4.7
80%
V
I
Fx
Fx
= 20 mA
= 3.4 V
Application Information
3
70%
5.1
IN
4
60%
is suf-
5.5
5
50%
t
LO
in 1 × mode unless, as V
the 150 mV threshold. When V
enters 1.5× mode.
When the A8530 switches from 1× to 2× mode, it first switches
to 1.5× mode for a typical duration of 1 ms before entering
2× mode.
When operating in 1.5× mode, if V
switches back to 1× mode every 130 ms, and then reenters 1.5×
mode again if necessary.
Transitions Between 1.5× and 2× Modes
The transition from 1.5× to 2× mode depends upon dropout
conditions.
When operating in 2× mode, the IC switches back to 1.5× mode
every 130 ms, and then reenters 2× mode again if necessary.
Furthermore, when in 2× mode, whenever a channel disabling
is sensed (that is, whenever ENM is held low for > 0.5 ms with
ENF high, or vice versa), the IC automatically reverts to 1.5×
mode, and then reenters 2× mode again if necessary.
Dimming
Display Backlight LED1 through LED4 Dimming The display
backlight LEDs (LED1 through LED4) brightness and on/off can
be controlled using digital input at the ENM pin. The ENM pin
accepts one-wire serial pulse input to enable the A8350 and to set
up to 11 dimming levels, from 100% down to 5%.
When ENM 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 10th pulse reduces the current by 5%. The next
pulse restores 100% (full) brightness. Figure 6 shows the timing
diagram for ENM control.
and Flash/Torch White LED Driver
Ultracompact 6-Channel Backlight
6
40%
7
30% 20%
t
HI
8
IN
9
10%
drops, the LEDx nodes fall below
115 Northeast Cutoff, Box 15036
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 [phone]
www.allegromicro.com
10
LEDx
5%
OUT
11
falls below 150 mV, the IC
100% 90%
< V
IN
, then the IC
t
SHDN
SHDN or
Dimming
Reset
8