Datasheet

ADP5520
Rev. A | Page 9 of 40
THEORY OF OPERATION
1
PGND
21
VBAT
16
VDDIO
5
SCL
4
SDA
3
nINT
15
nRST
ADP5520
4.7µH
1µF
1µF
1µF
VBAT
13
R3
6
R2
7
R1
8
R0
9
C0
10
C1
11
C2
12
C3
2
SW
22
BST BL_SNK
20
CAP_OUT
100nF
1918 24
GND GND GND
17
CMP_IN
07445-004
14
ILED
STATE MACHINE
REGISTER MAP
INTERRUPT/RESET
CONTROL
INTERFACE
BIAS/CLOCK
LIGHT
SENSOR
LED
CURRENT
CONTROL
POR
LDO
I/O CONFIG
GPIO/KEYPAD
IN
EN
OUT
2.7V
23
THERMAL S/D
BACKLIGHT
CURRENT
CONTROL
27V
BOOST
CONTROL
0.65V
OVP
AUTO
LOAD
I-LIMIT
FB
VBAT
Figure 13. Internal Block Diagram
The ADP5520 is a backlight white LED driver with an I/O port
expander. It is ideal for cell phone designs and other portable
devices, where keypad and/or extended I/O functionality is
needed. Programmable fade-in, fade-out, dim, and off timers
provide the backlight with flexible control features. Using an
external photodiode, the ADP5520 can perform ambient light
sensing, and adjust the backlight brightness according to
varying lighting conditions.
The I/O port expander has eight configurable GPIO pins. The
I/Os can be configured as a keypad matrix, digital inputs, or
digital outputs. Additionally, two of the I/Os (R3 and C3) can be
configured as current sink lines and, paired with a dedicated
sink line (ILED), can be used to drive up to three auxiliary LEDs.
Programmable fading is also available for auxiliary LEDs.
Once programmed through its I
2
C-compatible interface, the
ADP5520 can run autonomously. An interrupt line (nINT) is
available to alert an external microprocessor of the status of its
I/Os, keypad presses and releases, ambient light sensor comparator
states, and overvoltage conditions.
BACKLIGHT DRIVE AND CONTROL
White LEDs are common in backlighting the displays of modern
portable devices such as cell phones. White LEDs require a high
forward voltage, V
F
, before they conduct current and emit light.
Display panels, depending on their size, can be backlit with
single or multiple white LEDs. In panels that require multiple
LEDs, the LEDs are commonly connected in a series string to
achieve uniform brightness in each LED by passing a common
current through all of them. The LED string needs to be biased
with a voltage greater than the sum of the V
F
of each LED
before it conducts.
The ADP5520 is an asynchronous boost converter capable of
driving an LED string with 24.5 V (minimum). For detailed
information about the boost device, see the Applications
Information section. With sufficient forward voltage created,
the ADP5520 controls the current (and thus the brightness)
of the LED string via an adjustable internal current sink. An
internal state machine, in conjunction with programmable
timers, dynamically adjusts the current sink between 0 mA
and 30 mA to achieve impressive backlight control features.