AAT2860 Datasheet, PDF (11/23 Pages) Advanced Analogic Technologies – Backlight/Flash LED Driver and Multiple LDO Lighting Management Unit

PRODUCT DATASHEET
AAT2860
ChargePump^TM Backlight/Flash LED Driver and Multiple LDO Lighting Management Unit
Functional Block Diagram
IN IN
C1-
C1+
C2-
C2+
OUT
1x/1.5x/2x
Tri -mode
Charge pump
LDOA
LDOB
LDOC
SDA
SCL
LED_SEL
FL_LVL
LDO_SEL
AAT2860-x
REF
7
Control
Logic
PGND
AGND
BL1
BL2
BL3
BL4
BL5
BL6/FL1
BL7/FL2
Functional Description
The AAT2860-x is a highly integrated backlight and
photo-flash driver with three LDO regulators. The charge
pump LED driver powers the backlight and flash LEDs
from the 2.7V to 5.5V input voltage. The LDO regulators
get their power from the same input and produce regu-
lated output voltage between 1.5V and 3.0V. Control of
the LEDs and the LDO output voltage is through an I²C
compatible serial interface for easy programming.
LED Drivers
The AAT2860-x drives up to seven backlight LEDs up to
31mA each and up to two flash LEDs up to 300mA each.
The LEDs are driven from a charge pump to insure that
constant current is maintained over the entire battery
voltage range. The charge pump automatically switches
from 1x, 1.5x, and 2x modes and back to maintain the
LED current while minimizing power loss for high effi-
ciency. The charge pump operates at the high 1MHz
switching frequency allowing the use of small 1μF ceram-
ic fly capacitors.
The charge pump is controlled by the voltage across the
LED current sinks. When any one of the active backlight
current sink sink/channel voltages drops below 180mV
or the flash current sink/channel drops below 450mV,
the charge pump goes to the next higher mode (from 1x
to 1.5x or from 1.5x to 2x mode) to maintain sufficient
LED voltage for constant LED current. The AAT2860-x
continuously monitors the LED forward voltages and
uses the input voltage to determine when to reduce the
charge pump mode for better efficiency. There is also a
150mV mode-transition hysteresis that prevents the
charge pump from oscillating between modes.
LED Current Control
Both the backlight and flash LED currents are controlled
through an I²C compatible serial interface. The backlight
LED current can be set between 0.5mA and 31mA in
1mA steps while the flash LED current can be set
between 0mA and 300mA in 20mA steps. The backlight
LED currents match to within 3% while the flash LED
currents match to within 5%.
To eliminate the latency of the I²C compatible serial
interface, the flash LED is enabled through a dedicated
input, FL_LVL. The AAT2860-x also include a safety
timer that prevents overstress of the flash LED(s). This
is important because many flash LEDs operate for a brief
period beyond their steady-state operating limitations. If
the flash driving hardware and/or software fails to turn
2860.2008.05.1.0
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