ANALOG DEVICES ADP5520 Service Manual

www.BDTIC.com/ADI

Backlight Driver with I/O Expander

FEATURES

Efficient asynchronous boost converter for driving up to

6 white LEDs

2.7 V to 5.5 V input voltage range
128 programmable backlight LED current levels (30 mA

maximum)

Ambient light sensing with autonomous backlight

adjustment
Programmable backlight fade-in/fade-out times
Programmable backlight dim and off times
8 configurable GPIO pins (input, output, up to 4 × 4 keypad)
Up to 3 auxiliary LED current sinks (1 dedicated, 2 configurable)
64 programmable auxiliary LED current levels (14 mA

maximum)
Programmable auxiliary LED fade-in/fade-out times
Programmable auxiliary LED on and off times (allows

blinking)

2

I

C-compatible serial interface
Interrupt line for signaling an external processor (nINT)
Hard reset (nRST)
Current limit protection
Thermal overload protection
Available in small 4.0 mm × 4.0 mm, 24-lead LFCSP package

I/O RAIL

10kΩ

TYPICAL OPERATING CIRCUIT

VBAT

10kΩ

1µF

1

21

16

2.2kΩ

2.2kΩ

5

4

3

15

1µF

4.7µH

2SW22

PGND

VBAT

VDDIO

SCL

SDA

nINT

nRST

13R36R27R18R09C010C111C212

BST

ADP5520

I/O

I/O

ABCD

EFGH

Figure 1.

ADP5520

23

BL_SNK

GND

GND

GND

CMP_IN

ILED

14

VBAT

20

19

18

24

17

CAP_OUT

C3

1µF

100nF

VBAT

7445-001

APPLICATIONS

Display backlight driver for phones that require slider or flip

keypad functions with single or multiple LED indicators

GENERAL DESCRIPTION

The ADP5520 is a versatile single-chip, white LED backlight
driver with a user configurable I/O expander. This device fits
handset applications where the flip or slider section of the phone
requires backlighting, I/O signaling and detecting, auxiliary LED
lighting, and keypad functions. By incorporating an I
compatible serial interface and a single line interrupt, the
ADP5520 significantly reduces the total number of lines
required to interface with the baseband processor across the
hinge flex.

2

C®-

The ADP5520 can detect ambient light levels and adjust the
backlight brightness accordingly, resulting in extended battery
operation.

Once configured, the ADP5520 is capable of controlling the
flip/slider backlight intensity, on/off timing, dimming, and
fading without the intervention of the main processor, which
results in valuable battery power saving.

Rev. 0

Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registered trademarks are the property of their respective owners.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone] www.analog.com
Fax: [phone] ©2008 Analog Devices, Inc. All rights reserved.

ADP5520

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TABLE OF CONTENTS

Features .............................................................................................. 1

Applications ....................................................................................... 1 

Typical Operating Circuit ................................................................ 1

General Description ......................................................................... 1

Revision History ............................................................................... 2

Specifications ..................................................................................... 3

I2C Timing Specifications ............................................................ 4

Absolute Maximum Ratings ............................................................ 5

Thermal Resistance ...................................................................... 5

ESD Caution .................................................................................. 5

Pin Configuration and Function Descriptions ............................. 6

Typical Performance Characteristics ............................................. 7

Theory of Operation ........................................................................ 9

Backlight Drive and Control ....................................................... 9

Backlight Operating Levels ....................................................... 10

Backlight Maximum and Dim Settings ................................... 10

Backlight Turn On/Off/Dim ..................................................... 11

Automatic Dim and Turn Off Timers ..................................... 11

Linear Backlight Fade In and Fade Out ................................... 12

Fade Override ............................................................................. 13

Advanced Fading (Square) ........................................................ 13

Advanced Fading (Cubic 1 and Cubic 2) ................................ 14

Ambient Light Sensing .............................................................. 14

Automatic Backlight Adjustment ............................................. 15

I/O Expansion Pins (GPIOs) .................................................... 15

I/O Expansion Pins (Keypad Matrix) ...................................... 15

I/O Expansion Pins and ILED Pin (Auxiliary LED Current

Sinks) ............................................................................................ 17

Interrupt Output (nINT) ........................................................... 19

Reset Input (nRST) .................................................................... 19

Communication Interface ............................................................. 20

Register Map ................................................................................... 21

Detailed Register Descriptions ..................................................... 22

Applications Information .............................................................. 34

Converter Topology ................................................................... 34

PCB Layout ................................................................................. 35

Example Circuits ............................................................................ 36

Outline Dimensions ....................................................................... 38

Ordering Guide .......................................................................... 38



REVISION HISTORY

7/08—Revision 0: Initial Version

Rev. 0 | Page 2 of 40

ADP5520

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SPECIFICATIONS

VBAT = 2.7 V to 4.8 V, TJ = −40°C to +125°C, unless otherwise noted.1

Table 1.

Parameter Symbol Conditions Min Typ Max Unit

SUPPLY VOLTAGE

VBAT Input Voltage Range V
VDDIO Input Voltage Range V
Undervoltage Lockout Threshold UVLO
UVLO
UVLO
UVLO
SW leakage SW

SUPPLY CURRENT

Shutdown Current3 I
Standby Current4 I

BACKLIGHT LED DRIVER (SW, BST)

Current Limit (Peak Inductor Current) 450 600 750 mA
Switch On Resistance 100 200 400 mΩ
Overvoltage Limit 24.5 27 29.5 V
Boost Startup Time 1 ms

BACKLIGHT LED CURRENT SINK (BL_SNK)

Full-Scale Backlight Current 26 30 32 mA
Backlight Current Ramp Rate Fade timers disabled 0.3 mA/ms

AMBIENT LIGHT SENSOR (CMP_IN)

Full-Scale Current BL

INPUT LOGIC LEVELS (SCL, SDA, nRST, C0, C1, C2, C3, R0, R1, R2, R3)5

Logic Low Input Voltage VIL 1.8 V ≤ VDDIO ≤ 3.3 V2 0.3 × VDDIO V
Logic High Input Voltage VIH 1.8 V ≤ VDDIO ≤ 3.3 V2 0.7 × VDDIO V

Input Leakage Current V
INPUT LOGIC DEBOUNCE (nRST, C0, C1, C2, C3, R0, R1, R2, R3)6 V
PUSH-PULL OUTPUT LOGIC LEVELS (C0, C1, C2, C3, R0, R1, R2, R3)7

Logic Low Output Voltage VOL I

Logic High Output Voltage VOH I
OPEN-DRAIN OUTPUT LOGIC LEVELS (nINT, SDA)

Logic Low Output Voltage VOL I

Logic High Leakage Current V
AUX LED CURRENT SINK (ILED, C3, R3)8

Leakage LED

Full-scale Current Sink LED
GPIO PULL-UP RESISTANCE (C0, C1, C2, C3, R0, R1, R2, R3)9 50 65 80 kΩ
THERMAL SHUTDOWN

Thermal Shutdown Threshold TS TJ rising 150 °C

Thermal Shutdown Hysteresis TS

1

All limits at temperature extremes are guaranteed via correlation using standard statistical quality control (SQC). Typical values are at T

2

3.3 V or VBAT, whichever is smaller.

3

Internal LDO powered down, digital blocks inactive, I2C inactive, boost inactive.

4

Internal LDO powered up, digital blocks active, I2C active, boost inactive.

5

C0, C1, C2, C3, R0, R1, R2, and R3 are configured as digital inputs.

6

C0, C1, C2, C3, R0, R1, R2, and R3 are configured as digital inputs, with debounce enabled.

7

C0, C1, C2, C3, R0, R1, R2, and R3 are configured as digital outputs.

8

C3 and R3 are configured as digital inputs with pull-up.

9

C0, C1, C2, C3, R0, R1, R2, and R3 are configured as digital inputs with pull-up.

2.7 5.5 V

BAT

1.8 3.32 V

VDDIO

VBAT falling 1.7 2.1 V

VBAT

VBAT rising 2.4 2.7 V

VBAT

VDDIO falling 1.1 1.3 V

VDDIO

VDDIO rising 1.4 V

VDDIO

0.1 1 A

LEAKAGE

VDDIO = 0 V 0.1 1 A

SD

1.8 V ≤ VDDIO ≤ 3.3 V2,

STNBY

25 45 A

nSTNBY = 0

0.7 1 1.2 mA

FULLSCALE

1.8 V ≤ VDDIO ≤ 3.3 V2 0.1 1 µA

I-LEAKAGE

50 75 100 µs

IL-DBNC

= 1 mA 0.4 V

SINK

= 1 mA VDDIO − 0.2 V

SOURCE

= 1 mA 0.4 V

SINK

1.8 V ≤ VDDIO ≤ 3.3 V2 0.1 1 µA

OH-LEAKAGE

Sink disabled 0.1 1 µA

LEAKAGE

Applied pin voltage = 1 V 10.5 14 16.5 mA

FULLSCALE

T

HYS

falling 10 °C

J

= 25⁰C, VBAT = 3.6 V.

A

Rev. 0 | Page 3 of 40

ADP5520

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I2C TIMING SPECIFICATIONS

Table 2.

Parameter Description Min Max Unit

Delay from Reset Deassertion to I2C Access 60 s
f

SCL clock frequency 400 kHz

SCL

t

SCL high time 0.6 s

HIGH

t

SCL low time 1.3 s

LOW

t

Data setup time 100 ns

SU, DAT

t

Data hold time 0 0.9 s

HD, DAT

t

Setup time for repeated start 0.6 s

SU, STA

t

Hold time for start/repeated start 0.6 s

HD, STA

t

Bus free time for stop and start condition 1.3 s

BUF

t

Setup time for stop condition 0.6 s

SU, STO

tR Rise time for SCL and SDA 20 + 0.1 CB 300 ns
tF Fall time for SCL and SDA 20 + 0.1 CB 300 ns
tSP Pulse width of suppressed spike 0 50 s

1

C

Capacitive load for each bus line 400 pF

B

1

CB is the total capacitance of one bus line in picofarads.

SDA

t

t

LOW

SCL

S

S = START CONDI TION
Sr = REPEATED START CONDITION
P = STOP CO NDITION

t

R

t

HD, DAT

t

SU, DAT

t

HIGH

Figure 2. I

t

F

t

F

t

SU, STA

2

C Interface Timing Diagram

Sr P S

t

HD, STA

t

SP

t

SU, STO

BUF

t

R

07445-002

Rev. 0 | Page 4 of 40

ADP5520

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ABSOLUTE MAXIMUM RATINGS

Table 3.

Parameter Rating

VBAT to GND −0.3 V to +6 V
VDDIO to GND −0.3 V to VBAT
SW, BST to GND −0.3 V to +30 V
ILED, R0, R1, R2, R3, C0, C1, C2, C3, CMP_IN,

−0.3 V to +6 V
SCL, SDA, nINT, nRST, CAP_OUT, BL_SNK
to GND

PGND to GND −0.3 V to +0.3 V
Operating Ambient Temperature Range −40°C to +85°C1
Operating Junction Temperature Range −40°C to +125°C
Storage Temperature Range −65°C to +150°C
Soldering Conditions JEDEC J-STD-020

1

In applications where high power dissipation and poor thermal resistance

are present, the maximum ambient temperature may have to be derated.
Maximum ambient temperature (T
operating junction temperature (T
dissipation of the device (PD
resistance of the part/package in the application (θ
equation: T

A(MAX)

= T

J(MAXOP)

(MAX)

− (θJA × P

) is dependent on the maximum

A(MAX)

= 125°C), the maximum power

J(MAXOP)

), and the junction-to-ambient thermal

).

D(MAX)

), using the following

JA

THERMAL RESISTANCE

θJA is specified for the worst-case conditions, that is, a device
soldered in a circuit board for surface-mount packages.

Table 4. Thermal Resistance

Package Type θJA Unit

24-Lead LFCSP (CP-24-2) 50 °C/W

ESD CAUTION

Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.

Absolute maximum ratings apply individually only, not in
combination. Unless otherwise specified, all other voltages are
referenced to GND.

Rev. 0 | Page 5 of 40

ADP5520

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PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

VBAT

BST

BL_SNK

GND

CAP_OUT

GND

20

19

21

22

23

24

PIN 1
INDICATOR

1PGND
2SW
3nINT

ADP5520

4SDA

TOP VIEW

5SCL

(Not to Scal e)

6R2

9

7

8

R0

C0

NOTES

1. EXPOSED PAD MUST BE CONNE CTED
TO GROUND.

R1

Figure 3. Pin Configuration

Table 5. Pin Function Descriptions

Pin No. Mnemonic Description

1 PGND Power Switch Output to Ground.
2 SW Power Switch Input.
3 nINT Processor Interrupt. This pin is active low, open drain, and should be pulled up to VDDIO.
4 SDA I2C-Compatible Serial Data Line. Open drain requires external pull-up to VDDIO.
5 SCL I2C-Compatible Serial Clock Line. Open drain requires external pull-up to VDDIO.
6 R2 Row 2 when configured in a keypad matrix, D2 when configured as an I/O.
7 R1 Row 1 when configured in a keypad matrix, D1 when configured as an I/O.
8 R0 Row 0 when configured in a keypad matrix, D0 when configured as an I/O.
9 C0 Column 0 when configured in a keypad matrix, D4 when configured as an I/O.
10 C1 Column 1 when configured in a keypad matrix, D5 when configured as an I/O.
11 C2 Column 2 when configured in a keypad matrix, D6 when configured as an I/O.
12 C3 Column 3 when configured in a keypad matrix, D7 when configured as an I/O, LED 2 when configured as a current sink.
13 R3 Row 3 when configured in a keypad matrix, D3 when configured as an I/O, LED 3 when configured as a current sink.
14 ILED LED 1 Current Sink.
15 nRST

Reset Input, Active Low. This input signal resets the device to the power-up default conditions. Must be driven low
for 75 µs (typical) to be valid.

16 VDDIO

Supply Voltage for the I/O Pins. Voltage is 1.8 V to 3.3 V (or VBAT, whichever is smaller). If VDDIO = 0, the device goes

into full shutdown mode.
17 CMP_IN Input for Ambient Light Sensing.
18 GND Ground.
19 GND Ground.
20 CAP_OUT

Capacitor for Internal 2.7 V LDO. A 1 F capacitor must be connected between this pin and GND. Do not use this

pin to supply external loads.
21 VBAT Main Supply Voltage for the IC (2.7 V to 5.5 V).
22 BST Overvoltage Monitor Input for the Boost Converter.
23 BL_SNK Backlight Current Sink.
24 GND Ground.

18 G ND
17 CMP_IN
16 V DDIO
15 n RST
14 ILE D
13 R3

11

12

10

C2

C3

C1

07445-003

Rev. 0 | Page 6 of 40

ADP5520

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TYPICAL PERFORMANCE CHARACTERISTICS

VBAT = 3.6 V, TA = 25°C, unless otherwise noted. Inductor = LPS4012-472MLB. Schottky rectifier = MBR140SFT1G.

90

85

80

75

70

65

60

EFFICIE NCY (%)

55

50

45

40

024681012141618202224262830

BACKLIGHT CURRENT (mA)

6 LEDs, VBAT = 3. 0V
6 LEDs, VBAT = 3. 6V
6 LEDs, VBAT = 4. 2V
6 LEDs, VBAT = 5. 5V

Figure 4. Efficiency vs. Backlight Current (6 LEDS)

07445-047

48

40

TEMP = +25°C

32

24

16

8

STANDBY SUPPLY CURRENT (µA)

0

2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

TEMP = –40°C

TEMP = +85°C

VBAT (V)

Figure 7. Standby Supply Current vs. VBAT

07445-050

90

85

80

75

70

65

60

EFFICIE NCY (%)

55

50

45

40

024681012141618202224262830

BACKLIGHT CURRENT (mA)

6 LEDs, VBAT = 3. 6V
5 LEDs, VBAT = 3. 6V
4 LEDs, VBAT = 3. 6V

Figure 5. Efficiency vs. Backlight Current (4, 5, and 6 LEDS)

90

85

80

75

70

65

60

EFFICIE NCY (%)

55

50

45

40

024681012141618202224262830

BACKLIGHT CURRENT (mA)

6 LEDs, VBAT = 4.2V
6 LEDs, VBAT = 4.2V,

AUTOLOAD-ENABLED

Figure 6. Efficiency vs. Backlight Current (Autoload On/Off)

16

14

12

10

8

6

4

2

AUX LED FULL -SCALE SINK CURRENT (mA)

0

0 0.5 1.0 1.5 2.0 2.5 3.0

07445-048

AUX LED PIN VO LTAGE (V)

07445-051

Figure 8. Typical Auxiliary LED Pin (R3, C3, or ILED), Full-Scale Sink Current vs.

Applied Pin Voltage

07445-049

Rev. 0 | Page 7 of 40

ADP5520

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SW

1

INDUCTOR CURRENT

2

BST

BL_SNK

3

4

CH1 20.0V

CH3 10.0V

CH2 500mA

CH4 1.0V

Figure 9. Boost Operation (Backlight = 30 mA)

SW

1

INDUCTOR CURRENT

2

BST

TIME (4µs/DIV)

SW

1

INDUCTOR CURRENT

2

BST

BL_SNK

3

4

CH1 20.0V

07445-052

CH3 10.0V

CH2 500mA

CH4 1.0V

TIME (4µs/DIV)

07445-054

Figure 11. Boost Operation (Backlight = 2 mA)

SW

1

INDUCTOR CURRENT

2

BST

BL_SNK

3

4

CH1 20.0V

CH3 10.0V

CH2 500mA

CH4 1.0V

Figure 10. Boost Operation (Backlight = 15 mA)

TIME (4µs/DIV)

07445-053

3

4

BL_SNK

CH1 10.0V

CH3 10.0V

CH2 500mA

CH4 1.0V

TIME (1ms/DIV)

Figure 12. Boost Startup

07445-055

Rev. 0 | Page 8 of 40

ADP5520

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THEORY OF OPERATION

VBAT

1µF

4.7µH

1µF

PGND

VBAT

VDDIO

CAP_OUT

1µF

SCL

SDA

nINT

nRST

1

21

16

20

5

4

3

15

GND GND GND

2

POR

INTERFACE

ADP5520

1918 24

SW

I-LIMIT

BOOST

CONTROL

IN

EN

LDO

OUT

2.7V

BIAS/CLOCK

I/O CONF IG

GPIO/KEYPAD

6R27R18R09C010C111

27V

THERMAL S/D

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.

BST BL_SNK

22

AUTO
LOAD

OVP

STATE MACHINE

REGISTER MAP

INTERRUPT/ RESET

CONTROL

13

R3

C2

FB

BACKLIGHT

CURRENT

CONTROL

12

C3

ILED

14

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.

23

0.65V

VBAT

100nF

07445-004

of each LED

F

LIGHT

SENSOR

LED
CURRENT
CONTROL

, before they conduct current and emit light.

F

17

CMP_IN

Rev. 0 | Page 9 of 40

ADP5520

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BACKLIGHT MAXIMUM AND DIM SETTINGS

The backlight maximum and dim current settings are deter­mined by a 7-bit code programmed by the user into the registers
listed in the Backlight Operating Levels section. This 7-bit
resolution allows the user to set the backlight to 1 of 128
different levels between 0 mA and 30 mA. The ADP5520 can
implement two distinct algorithms to achieve a linear and a
nonlinear relationship between input code and backlight
current. The BL_LAW bits in Register 0x02 are used to swap
between algorithms.

By default, the ADP5520 uses a linear algorithm (BL_LAW =

00), where backlight current increases linearly for a correspond­ing increase of input code. Backlight current (in mA) is determined
by the following equation:

Backlight Current = Code × (Fullscale_Current/127) (1)

where:

Code is the input code programmed by the user.
Fullscale_Current is the maximum sink current allowed

(typically 30 mA).

The ADP5520 can also implement a nonlinear (square approxima­tion) relationship between input code and backlight current level.
In this case (BL_LAW = 01), the backlight current (in mA) is
determined by the following equation:

2

⎞
⎟
⎟
⎠

07445-007

Backlight Current =

⎛
⎜

×

Code (2)

⎜
⎝

127

CurrentFullscale

_

Figure 16 shows the backlight current level vs. input code for
both the linear and square law algorithms.

30

25

20

15

10

BACKLIGHT CURRENT (mA)

5

0

0 32 64 96 128

LINEAR

SQUARE

SINK CODE

Figure 16. Backlight Current vs. Sink Code

DAYLIGHT_MAX

DAYLIGHT_DIM

OFFICE_MAX

OFFICE_DIM

DARK_MAX

DARK_DIM

BL_LVL

MUX

BST

BL_OFFT
BL_DIMT

BL_FI

BL_FO

BL_VALUE

COUNTERS

AND

CONTROL

LOGIC

BL_SNK

BL_EN

DIM_EN

BL_LAW

CLOCK

GENERATOR

Figure 14. Backlight Brightness Control

BACKLIGHT OPERATING LEVELS

Backlight brightness control can operate in three distinct levels:
daylight (L1), office (L2), and dark (L3). The BL_LVL bits in
Register 0x02 control the level in which the backlight operates.
The BL_LVL bits can be changed manually, or if in automatic
mode, by the ambient light sensor (see the Ambient Light Sensing
section). By default, the backlight operates at daylight level
(BL_LVL = 00), where the maximum brightness is set using
Register 0x05 (DAYLIGHT_MAX). A daylight dim setting can
also be set using Register 0x06 (DAYLIGHT_DIM). When operat­ing at office level (BL_LVL = 01), the backlight maximum and
dim brightness settings are set by Register 0x07 (OFFICE_MAX)
and Register 0x08 (OFFICE_DIM). When operating at dark
level (BL_LVL = 10), the backlight maximum and dim brightness
settings are set by Register 0x09 (DARK_MAX) and Register 0x0A
(DARK_DIM).

D

30mA

BACKLIGHT CURRENT

0

LIGHT ( L1) OFFICE (L2) DARK (L3)

DAYLIGHT_MAX

OFFICE_MAX

DARK_MAX

DAYLIGHT_DIM

OFFICE_DIM

DARK_DIM

BACKLIGHT OPERATING LEVELS

Figure 15. Backlight Operating Levels

07445-005

07445-006

Rev. 0 | Page 10 of 40

ADP5520

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BACKLIGHT TURN ON/OFF/DIM

With the device in operating mode (nSTNBY = 1), the backlight
can be turned on using the BL_EN bit in Register 0x00. Before
turning on the backlight, the user should choose which level
(daylight (L1), office (L2), or dark (L3)) to operate in, and ensure
that maximum and dim settings are programmed for that level.
The backlight turns on when BL_EN = 1. The backlight turns
off when BL_EN = 0.

BACKLIGHT

CURRENT

MAX

AUTOMATIC DIM AND TURN OFF TIMERS

The user can program the backlight to dim automatically by
using the BL_DIMT timer in Register 0x03. The dim timer has
15 settings ranging from 10 sec to 2 min. The user should
program the dim timer before turning on the backlight. If
BL_EN = 1, the backlight turns on to its maximum setting, and
the dim timer starts counting. When the dim timer expires, the
internal state machine sets DIM_EN = 1, and the backlight goes
to its dim setting.

BACKLIGHT

CURRENT

MAX

DIM

DIM TIME R

RUNNING

DIM TIMER

RUNNING

BL_EN = 1 BL_EN = 0

Figure 17. Backlight Turn On/Off

07445-008

While the backlight is on (BL_EN = 1), the user can make it
change to a dim setting by programming DIM_EN = 1 in
Register 0x00. If DIM_EN = 0, the backlight reverts to its
maximum setting.

BACKLIGHT

CURRENT

MAX

DIM

BL_EN = 1

Figure 18. Backlight Turn On/Dim/Off

DIM_EN = 1 DIM_EN = 0 BL_EN = 0

07445-009

The maximum and dim settings can be set between 0 mA and
30 mA; therefore, it is possible to program a dim setting that is
greater than a maximum setting. For normal expected operation,
users should ensure that the dim setting is programmed to be less
than the maximum setting.

It is also possible to activate the backlight automatically when a
key press is detected. With the row and column pins configured as
a keypad matrix, and the KP_BL_EN bit asserted in Register 0x02,
the internal state machine asserts BL_EN and turns on the back­light if a key is pressed. See the I/O Expansion Pins (Keypad
Matrix) section for more information on using keypad
functionality.

BL_EN = 1

SET BY USER
SET BY INTERNAL STATEMACHINE

Figure 19. Dim Timer

BL_EN = 1

OR

DIM_EN = 1

BL_EN = 0DIM_EN = 1 DIM_EN = 0

If the user clears the DIM_EN bit (or reasserts the BL_EN bit),
the backlight reverts to its maximum setting and the dim timer
begins counting again. When the dim timer expires, the internal
state machine again sets DIM_EN = 1, and the backlight goes to
its dim setting. Reasserting BL_EN at any point during the dim
timer countdown causes the timer to reset and begin counting
again. The backlight can be turned off at any point during the
dim timer countdown by clearing BL_EN.

The user can also program the backlight to turn off automati­cally by using the BL_OFFT timer in Register 0x03. The off
timer has 15 settings ranging from 10 sec to 2 min. The user
should program the off timer before turning on the backlight.
If BL_EN = 1, the backlight turns on to its maximum setting,
and the off timer starts counting. When the off timer expires,
the internal state machine clears the BL_EN bit, and the
backlight turns off.

BACKLIGHT

CURRENT

MAX

OFF TIMER

RUNNING

07445-010

Rev. 0 | Page 11 of 40

SET BY USER
SET BY INTERNAL STATE MACHINE

BL_EN = 1 BL_EN = 0

Figure 20. Off Timer

07445-011

ADP5520

A

www.BDTIC.com/ADI

Reasserting BL_EN at any point during the off timer countdown
causes the timer to reset and begin counting again. The backlight
can be turned off at any point during the off timer countdown
by clearing BL_EN.

The dim timer and off timer can be used together for sequential
maximum-to-dim-to-off functionality. With both the dim and
off timers programmed, if BL_EN is asserted, the backlight turns
on to its maximum setting. When the dim timer expires, the
backlight changes to its dim setting. When the off timer expires,
the backlight turns off.

BACKLIGHT

CURRENT

MAX

DIM

SET BY USER
SET BY INTERNAL STATE MACHINE

DIM TIMER

RUNNING

OFF TIMER

RUNNING

BL_EN = 1 BL _EN = 0DIM_EN = 1

Figure 21. Dim and Off Timers Used Together

LINEAR BACKLIGHT FADE IN AND FADE OUT

To counteract the abrupt visual effect of near instant turn-on
and turn-off of the backlight, the ADP5520 contains timers to
facilitate the smooth fading between off, on, and dim states. By
default (BL_LAW = 00), the ADP5520 implements a fading
scheme using the linear backlight code algorithm (see Equation 1).

The BL_FI timer in Register 0x04 can be used for smooth fade-in
transitions from low to high backlight settings, such as off-to-dim,
off-to-maximum, and dim-to-maximum. The BL_FI timer can be
programmed to one of 15 settings ranging from 0.3 sec to 5.5 sec.
The BL_FI timer should be programmed before asserting BL_EN.

30.0

27.5

25.0

22.5

20.0

17.5

15.0

12.5

10.0

7.5

BACKLIGHT CURRENT (mA)

5.0

2.5

0

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5

FADE-IN TIME (s)

Figure 22. Linear Fade-In Times

0.3 SEC

0.6 SEC

0.9 SEC

1.2 SEC

1.5 SEC

1.8 SEC

2.1 SEC

2.4 SEC

2.7 SEC

3.0 SEC

3.5 SEC

4.0 SEC

4.5 SEC

5.0 SEC

5.5 SEC

07445-013

Rev. 0 | Page 12 of 40

07445-012

The time programmed in BL_FI represents the time it takes the
backlight current to go from 0 mA to 30 mA. Fading between
intermediate settings is shorter.

The BL_FO timer in Register 0x04 can be used for smooth fade­out transitions from high to low backlight settings such as
maximum-to-dim and dim-to-off. The BL_FO timer can be
programmed to one of 15 settings ranging from 0.3 sec to 5.5 sec.
The BL_FO timer should be programmed before asserting BL_EN.

30.0

27.5

25.0

22.5

20.0

17.5

15.0

12.5

10.0

7.5

BACKLIGHT CURRENT (mA)

5.0

2.5

0

0 0.51.01.52.02.53.03.54.04.55.05.5

FADE-OUT TI ME (s)

Figure 23. Linear Fade-out Times

0.3 SEC

0.6 SEC

0.9 SEC

1.2 SEC

1.5 SEC

1.8 SEC

2.1 SEC

2.4 SEC

2.7 SEC

3.0 SEC

3.5 SEC

4.0 SEC

4.5 SEC

5.0 SEC

5.5 SEC

07445-014

The time programmed in BL_FO represents the time it takes
the backlight current to go from 30 mA to 0 mA. Fading
between intermediate settings is shorter.

Figure 24 shows the fade timers in use. With BL_FI and BL_FO
programmed, if BL_EN is asserted, then the backlight fades in
to its maximum setting. If DIM_EN is asserted, then the backlight
fades out to its dim setting. If BL_EN is cleared, the backlight
fades out to off.

F

BACKLIGHT

CURRENT

FADE -IN

OFF-TO-MAX

MAX

DIM

BL_EN = 1 BL_EN = 0 BL_EN = 0 BL_EN = 0

DIM_EN = 1

SET BY USER

DE-OUT

MAX-TO-DIM

FADE-OUT

DIM-TO-OF F

FADE-OUT FADE-I N

FADE -OU TFADE-IN

BL_EN = 1 BL_EN = 1

Figure 24. Backlight Turn On/Off/Dim with Fade Timers

During any point in a fade-out, if BL_EN is asserted, then the
backlight stops at its current fade-out position and begins
fading in.

The fade-in and fade-out timers can be used independently of each
other, that is, fade-in can be enabled while fade-out is disabled.
The fade timers can also be used with the off and dim timers.

07445-015