ADP5501 Analog Devices, ADP5501 Datasheet - Page 9

• Manufacturer Part Number: ADP5501
• Description: Programmable Current Backlight Driver with Ambient Light Sensor Input
• Manufacturer: Analog Devices

Specifications of ADP5501

• 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 ADP5501 is an autonomous backlight white LED driver
with programmable current and ambient light sensor input. It is
ideal for cellular phone designs and other portable devices,
where programmable and automated light output is needed. Its
versatility makes it ideal for media-enabled mobile devices.
Programmable fade-in, fade-out, dim, and off timers provide
the backlight with excellent flexibility and control features.
Using an external photodiode, the ADP5501 can perform
ambient light sensing and adjust the backlight brightness
according to varying lighting conditions.
Programmable fading is also available for the three LED sinks.
Once programmed through its I
ADP5501 can run autonomously. An interrupt line ( INT ) is
available to alert an external microprocessor of the status of its
ambient light sensor comparator states, current limit, thermal
overload, and overvoltage conditions.
BACKLIGHT DRIVE 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
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, however, needs to be biased with a voltage
greater than the sum of each LED V
2.7V TO 5.5V
CAP_OUT
1µF
1µF
VDDIO
PGND
VBAT
2
C-compatible interface, the
F
SDA
4.7µH
SCL
RST
INT
(typically, 3.5 V), before they
F
before it can conduct.
21
16
20
15
1
5
4
3
POR
GND
18
INTERFACE
GND
2
19
EN
SW
BIAS/CLOCK
GND
24
LDO
CONTROL
I-LIMIT
IN
OUT
Figure 13. Internal Block Diagram
2.7V
BOOST
NC
6
NC
OVP
Rev. 0 | Page 9 of 28
7
ADP5501
NC
1µF
8
INTERRUPT/RESET
NC
STATE MACHINE
9
REGISTER MAP
NC
CONTROL
10
22
27V
BST
FB
NC
11
To achieve this high voltage, the ADP5501 contains a nonsyn-
chronous boost device capable of driving an LED string with an
OVP limited to 24.5 V(minimum). For detailed information
about the boost device, see the Applications Information
section. With sufficient forward voltage created, the ADP5501
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.
DAYLIGHT_MAX
LED2
DAYLIGHT_DIM
PROTECTION
0.65V
OFFICE_MAX
OFFICE_DIM
DARK_MAX
13
THERMAL
DARK_DIM
BL_LVL
LED1
12
BACKLIGHT
CONTROL
CURRENT
LED0
14
SENSOR
Figure 14. Backlight Brightness Control
BL_SNK
LIGHT
CURRENT
CONTROL
MUX
LED
23
BL_OFFT
BL_DIMT
BL_FO
BL_FI
BST
17
CMP_IN
COUNTERS
BL_VALUE
CONTROL
LOGIC
100nF
AND
VBAT
ADP5501
GENERATOR
BL_LAW
DIM_EN
CLOCK
BL_EN
BL_SNK