ADP5520 Analog Devices, ADP5520 Datasheet - Page 9

• Manufacturer Part Number: ADP5520
• Description: Backlight Driver with I/O Expander
• Manufacturer: Analog Devices

Specifications of ADP5520

• Vin Range: 2.7 to 5.5V
• Vout (v): 24 to 27
• Synchronous: No
• Package: 24-Lead LFCSP
• Led Configuration: Serial
• Topology: Inductive
• I2c Support: Yes
• Max Iout (ma): 30mA
• Brightness Control: I2C
• Switching Frequency: 1MHz
• Over Volt Protection (v): 24V

THEORY OF OPERATION
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
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.
VBAT
CAP_OUT
1µF
1µF
VDDIO
PGND
VBAT
nRST
nINT
SDA
4.7µH
SCL
2
C-compatible interface, the
20
21
16
15
1
5
4
3
GND GND GND
18
ADP5520
POR
19
INTERFACE
2
24
EN
SW
BIAS/CLOCK
LDO
R2
6
I-LIMIT
CONTROL
IN
OUT
2.7V
BOOST
R1
GPIO/KEYPAD
7
Figure 13. Internal Block Diagram
I/O CONFIG
27V
R0
8
1µF
C0
9
THERMAL S/D
Rev. A | Page 9 of 40
INTERRUPT/RESET
C1
10
OVP
STATE MACHINE
22
REGISTER MAP
BST
C2
CONTROL
11
AUTO
LOAD
R3
13
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
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
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.
C3
12
BACKLIGHT
FB
CURRENT
CONTROL
ILED
14
SENSOR
BL_SNK
LIGHT
CURRENT
CONTROL
0.65V
LED
F
, before they conduct current and emit light.
23
17
CMP_IN
100nF
VBAT
F
of each LED
ADP5520