Datasheet

ADP8860
Rev. 0 | Page 12 of 52
THEORY OF OPERATION
The ADP8860 combines a programmable backlight LED charge
pump driver with automatic phototransistor control. This combi-
nation allows for significant power savings because it is able to
change the current intensity based on the lighting conditions. It
performs this function automatically thereby removing the
need for a processor to monitor the phototransistor. The light
intensity levels are fully programmable via the I
2
C interface. A
second phototransistor input, with dedicated comparators,
improves the ambient light detection abilities for various user-
operating conditions.
The ADP8860 allows up to seven LEDs to be independently
driven up to 30 mA (typical). The seventh LED can also be
driven to 60 mA (typical). All LEDs can be individually pro-
grammed or combined into a group to operate backlight LEDs.
A full set of safety features including short-circuit, overvoltage,
and overtemperature protection with input-to-output isolation
allow for a robust and safe design. The integrated soft start
limits inrush currents at startup, restart attempts, and gain
transitions.
C1
1µF
C2
1µF
GND2
D1
nINT
CMP_IN
C3
D2
C
OUT
VOUT
A2
C
IN
VIN
V
REFS
I
REFS
STNDBY
EN
VIN
VBAT
C1+
SDA
C2
SCL
E2
I
2
C
LOGIC
VDDIO
STNDBY
SWITCH CONTROL
ILED CONTROL
A1
C1
B1
B2
C1–
C2+
C2–
nRST
E1
NOISE FILTER
50µs
RESET
A3
D2
E3
D3
E4
D4
D4
D5
C4
D6
B4
D7
B3
D1
D3
V
ALS
OPTIONAL
PHOTOSENSOR
ID1
ID2
ID3
ID4 ID5
ID6
ID7
GAIN
SELECT
LOGIC
CHARGE
PUMP
LOGIC
V
IN
LIGHT
SENSOR
LOGIC
GND1
A4
CLK
UVLO
PHOTOSENSOR
CONVERSION
CHARGE
PUMP
(1×, 1.5×, 2×)
SOFT START
07967-011
I
SS
Figure 26. Detailed Block Diagram