DATA SHEET
AAT2848
High Current Charge Pump For Backlight Display and Flash Applications
General Description
Features
The AAT2848 is a tri-mode charge pump optimized for
systems operating with lithium-ion/polymer batteries. The
charge pump provides power for both white LED backlight
and flash, with an integrated four channel backlight LED
current sink plus two channel flash LED current sinks.
•
•
•
•
Each backlight channel can drive up to 30mA, while each
flash current sink/channel can drive up to 300mA (600mA
total). Two independent S2Cwire™ (Skyworks' Simple
Serial Control™) serial digital interface inputs enable,
disable, and set LED current to one of 32 levels for the
backlight and to one of 16 levels for the flash, with fullscale current independently set for backlight and flash
using external resistors.
The AAT2848 offers a built-in fade-in/out function for
linear control of the backlight current during ON/OFF
transitions. The fade time is programmable by an external capacitor.
The AAT2848 also offers a built-in flash timeout function
as a safety feature associated with the high power flash
driver. The safety timer is also programmable via an
external capacitor.
The AAT2848 is equipped with built-in short-circuit and
over-temperature protection. The soft-start circuitry prevents excessive inrush current at start-up and mode
transitions. The AAT2848 is available in a Pb-free, space
saving TQFN33-20 package and operates over the -40°C
to +85°C ambient temperature range.
•
•
•
•
•
•
•
•
•
•
Tri-Mode (1x/1.5x/2x) Charge Pump
Four 30mA Backlight LED Channels
Independent S2Cwire Control for Backlight
32-Level Programmable Backlight Current Control—
Linear, Inverting
Two 300mA Flash LED Channels
Independent S2Cwire Control for Flash
16-Level Programmable Flash Current Control—
Linear, Inverting
User-Programmable Full Scale Current for Backlight
and Flash
User-Programmable Fade-In/Fade-Out Function for
Backlight
User-Programmable Safety Timer for Flash LED
Protection
Built-In Thermal Protection
Automatic Soft-Start
-40°C to +85°C Temperature Range
Available in TQFN33-20 Package
Applications
• Camera Enabled Mobile Devices
• Digital Still Cameras
• Multimedia Mobile Phones
Typical Application
C1
1μF
C2
1μF
C1- C1+ C2IN
VBAT
CIN
4.7μF
S2Cwire
Backlight Control
S2Cwire
Flash Control
C2+
WLEDs
OSRAM LW M673
or equivalent
OUT
AAT2848
BENS
FENS
BSET
COUT
2.2μF
Flash LEDs
Lumileds PWF1
or equivalent
BL1
BL2
BL3
BL4
FL1
FL2
FSET
RBSET
15k
RFSET
14.3k
FLTMR
CFLTMR
330nF
FADE
CFADE
47nF
AGND
PGND
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202069A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012
1
DATA SHEET
AAT2848
High Current Charge Pump For Backlight Display and Flash Applications
Pin Descriptions
Pin #
Symbol
1
OUT
2
3
C2+
AGND
4
FADE
5
FLTMR
6
BENS
7
FENS
8
FSET
9
BSET
10
BL1
11
BL2
12
BL3
13
BL4
14
FL1
15
FL2
16
17
18
PGND
C2C1-
19
IN
20
EP
C1+
Description
Charge pump output; supplies current to the backlight and flash LEDs. Connect the backlight and flash LED anodes to OUT. Bypass OUT to PGND with a 2.2μF or larger ceramic capacitor as close to the AAT2848 as possible.
Positive terminal of charge pump capacitor 2. Connect a 1μF charge pump capacitor 1 from C2+ to C2-.
Analog ground. Connect AGND to PGND at a single point as close to the AAT2848 as possible.
Fade-In/Fade-Out timing control capacitor input. Connect a capacitor from FADE to AGND to set the automatic backlight current fade-in/fade-out response time. A 47nF capacitor sets the fade-in/fade-out backlight
response time to 2.7 seconds. Connect to the IN pin to disable fade functionality.
Flash timer control capacitor input. Connect a capacitor from FLTMR to AGND to set the flash timer. A 330nF
capacitor sets the flash timer to 1.3 seconds. Connect to the AGND pin to disable timer functionality.
Backlight enable and serial control input. BENS is the on/off control for the backlight and the S2Cwire input to
serially control the backlight LED brightness relative to the maximum current set by the resistor at BSET.
Flash enable and serial control input. FENS is the on/off control for the flash and the S2Cwire input to serially
control the flash LED brightness relative to the maximum current set by the resistor at FSET.
Flash current setting input. A 9.53k resistor from FSET to AGND sets the maximum flash LED current to
300mA per flash output.
Backlight current setting input. A 10k resistor from BSET to AGND sets the maximum backlight LED current
to 30mA per backlight output.
Backlight LED 1 current sink/channel. BL1 controls the current through backlight LED 1. Connect the cathode
of backlight LED 1 to BL1. If not used, connect BL1 to OUT.
Backlight LED 2 current sink/channel. BL2 controls the current through backlight LED 2. Connect the cathode
of backlight LED 2 to BL2. If not used, connect BL2 to OUT.
Backlight LED 3 current sink/channel. BL3 controls the current through backlight LED 3. Connect the cathode
of backlight LED 3 to BL3. If not used, connect BL3 to OUT.
Backlight LED 4 current sink/channel. BL4 controls the current through backlight LED 4. Connect the cathode
of backlight LED 4 to BL4. If not used, connect BL4 to OUT.
Flash LED 1 current sink/channel. FL1 controls the current through flash LED 1. Connect the cathode of flash
LED 1 to FL1. If not used, connect FL1 to OUT.
Flash LED 2 current sink/channel. FL2 controls the current through flash LED 2. Connect the cathode of flash
LED 2 to FL2. If not used, connect FL2 to OUT.
Power ground. Connect PGND to AGND at a single point as close to the AAT2848 as possible.
Negative terminal of charge pump capacitor 2.
Negative terminal of charge pump capacitor 1.
Power input. Connect IN to the input source voltage. Bypass IN to PGND with a 4.7μF or larger ceramic
capacitor as close to the AAT2848 as possible.
Positive terminal of charge pump capacitor 1. Connect a 1μF charge pump capacitor 1 from C1+ to C1-.
Exposed paddle (bottom). Connect to ground as close as possible to the device.
Pin Configuration
PGND
C2C1IN
C1+
16
17
18
19
20
OUT
C2+
AGND
FADE
FLTMR
1
15
2
14
3
13
EP
4
12
5
11
FL2
FL1
BL4
BL3
BL2
9
10
8
7
6
BL1
BSET
FSET
FENS
BENS
2
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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DATA SHEET
AAT2848
High Current Charge Pump For Backlight Display and Flash Applications
Absolute Maximum Ratings1
Symbol
VN
VN
VN
TJ
TLEAD
Description
IN, OUT, BL1, BL2, BL3, BL4, FL1, FL2, C1-, C2- Voltage to GND
C1+, C2+ Voltage to GND
BENS, FENS, BSET, FSET, FLTMR, FADE Voltage to GND
Operating Junction Temperature Range
Maximum Soldering Temperature (at leads, 10 sec)
Value
Units
-0.3 to 6.0
-0.3 to VOUT + 0.3
-0.3 to VIN + 0.3
-40 to 150
300
V
V
V
°C
°C
Value
Units
2.0
50
W
°C/W
Thermal Information2, 3, 4
Symbol
PD
JA
Description
Maximum Power Dissipation
Maximum Thermal Resistance
1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions
specified is not implied. Only one Absolute Maximum Rating should be applied at any one time.
2. Based on long-term current density limitation.
3. Derate 20mW/°C above 25°C ambient temperature.
4. Mounted on a 1.6mm-thick FR4 circuit board.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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3
DATA SHEET
AAT2848
High Current Charge Pump For Backlight Display and Flash Applications
Electrical Characteristics1
VIN = 3.6V; CIN = 4.7μF; COUT = 2.2μF; C1 = C2 = 1μF; RBSET = 15kΩ; RFSET = 14.3kΩ; CFLTMR = 0.33μF; CFADE = 47nF;
TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25°C.
Symbol
VIN
IIN(Q)
Description
IN Operating Voltage Range
IN Operating Current
IIN(SHDN)
IN Shutdown Current
TSD
Thermal Shutdown
TSD(HYS)
Thermal Shutdown Hysteresis
Charge Pump Section
IOUT(MAX)
CP Maximum Output Current
Charge Pump Mode Transition
VIN(TH_H)
Hysteresis
Charge Pump Oscillator
fOSC
Frequency (1.5X mode)
Charge Pump Soft Start Time
tSS
BL1-BL4 Backlight LED Outputs
IBL_(MAX)
BL1-BL4 Current Accuracy
I(BL_)
BL1-BL4 Current Matching
BL1-BL4 Charge Pump Mode
VBL_(TH)
Transition Threshold
FL1-FL2 Flash LED Outputs
IFL_(MAX)
I(FL_)
VFL_(TH)
4
Conditions
FL1-FL2 Current Accuracy
FL1-FL2 Current Matching
FL1-FL2 Charge Pump Mode
Transition Threshold
Min
Typ
Max
Units
5.5
V
600
μA
5.5
mA
600
μA
5.5
mA
1.0
μA
°C
°C
2.7
BENS = IN, FENS = AGND, BL1 = BL2 = BL3 = BL4 = OUT
(Excluding LED Current)
BENS = IN, FENS = AGND, BL1 = BL2 = BL3 = BL4 = OPEN
(1.5x CP, no load)
BENS = AGND, FENS = IN, FL1 = FL2 = OUT
(Excluding LED Current)
BENS = AGND, FENS = IN, FL1 = FL2 = OPEN
(2x CP, no load)
BENS = FENS = AGND
140
15
IN = 3V
720
mA
BENS = DATA1
100
mV
TA = 25°C
1.0
MHz
100
μs
BENS = DATA1; VIN – VF = 1.5V
BENS = DATA32; VIN – VF = 1.5V
BENS = DATA1; VIN – VF = 1.5V
18
0.26
Any backlight current sink/channel BL1, BL2, BL3, BL4
FENS = DATA1; VIN – VF = 1.5V
FENS = DATA16; VIN – VF = 1.5V
FENS = DATA1; VIN – VF = 1.5V
Any flash current sink/channel FL1, FL2
20
0.32
±3
22
0.39
%
120
180
5.66
200
6.66
±3
mV
220
7.66
300
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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mA
mA
%
mV
DATA SHEET
AAT2848
High Current Charge Pump For Backlight Display and Flash Applications
Electrical Characteristics1
VIN = 3.6V; CIN = 4.7μF; COUT = 2.2μF; C1 = C2 = 1μF; RBSET = 15kΩ; RFSET = 14.3kΩ; CFLTMR = 0.33μF; CFADE = 47nF;
TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25°C.
Symbol
Description
BENS and FENS Logic Control
VBENS(L),
BENS, FENS Input Low Threshold Voltage
VFENS(L)
VBENS(H),
BENS, FENS Input High Threshold Voltage
VFENS(H)
IBENS, IFENS BENS, FENS Input Leakage Current
tFADE
Automatic Fade-In/Out Timer
tFLASH
tBENS(LOW),
tFENS(LOW)
Automatic Flash Disable Time
tBENS(HI_MIN),
tFENS(HI_MIN)
tBENS(HI_MAX),
tFENS(HI_MAX)
tBENS(OFF),
tFENS(OFF)
tBENS(LAT),
tFENS(LAT)
BENS, FENS Low Time
Minimum BENS, FENS High Time
Conditions
Min
Typ
Max
Units
0.4
V
1.4
VBENS = VFENS = VIN = 5V
BENS Transition High-to-Low or Low-toHigh; DATA1
FENS Transition Low-to-High
V
-1
1
μA
2.7
s
1.3
s
0.3
75
50
Maximum BENS, FENS High Time
μs
ns
75
μs
BENS, FENS Off Timeout
500
μs
BENS, FENS Latch Timeout
500
μs
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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5
DATA SHEET
AAT2848
High Current Charge Pump For Backlight Display and Flash Applications
Typical Characteristics
Backlight Efficiency vs. Input Voltage
Backlight Current Matching vs. Temperature
(VIN = 3.6V; 30mA/Channel)
100
30.5
Efficiency (%)
90
Output Current (mA)
30mA/ch, VF = 3.4V
15mA/ch, VF = 3.2V
7.5mA/ch, VF = 3.0V
80
70
60
50
40
2.7
3.1
3.5
3.9
4.3
4.7
5.1
30.0
D1
D2
D3
D4
29.5
29.0
-40
5.5
-15
10
35
60
85
Temperature (°C)
Input Voltage (V)
Flash Efficiency vs. Input Voltage
Flash Current Matching vs. Temperature
(VIN = 3.6V; 150mA/Channel)
100
151mA/ch, VF = 3.0V
70mA/ch, VF = 2.9V
Efficiency (%)
90
80
70
60
50
40
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Output Current (mA)
152
151
150
149
148
147
-40
D1
D2
-15
VEN/SET
(2V/div)
VOUT
(2V/div)
VBLX
(2V/div)
IIN
(200mA/div)
35
60
85
Turn-On to 1x Mode Backlight
Turn-On to 1.5x Mode Backlight
(VIN = 4.5V; 30mA/Channel)
(VIN = 3.6V; 30mA/Channel)
0V
VEN/SET
(2V/div)
0V
0V
VOUT
(2V/div)
0V
VBLX
(2V/div)
0V
IIN
(200mA/div)
0A
Time (100μs/div)
6
10
Temperature (°C)
Input Voltage (V)
0V
0A
Time (100μs/div)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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DATA SHEET
AAT2848
High Current Charge Pump For Backlight Display and Flash Applications
Typical Characteristics
Turn-On to 2x Mode Flash
Turn-On to 1.5x Mode Flash
(VIN = 2.8V; 151mA/Channel)
(VIN = 3.6V; 151mA/Channel)
VEN/SET
(2V/div)
0V
VEN/SET
(2V/div)
VOUT
(2V/div)
0V
VOUT
(2V/div)
VFLX
(2V/div)
IIN
(400mA/div)
VFLX
(2V/div)
0V
IIN
(400mA/div)
0A
0V
0V
0V
0A
Time (100μs/div)
Time (100μs/div)
Turn-Off from 1.5x Mode Backlight
Turn-Off from 1.5x Mode Flash
(VIN = 3.6V; 30mA/Channel; Fade-In/Out Disabled)
(VIN = 3.6V; 151mA/Channel)
VEN/SET
(2V/div)
VF
(1V/div)
IIN
(200mA/div)
VEN/SET
(2V/div)
0V
VF
(1V/div)
0V
IIN
(400mA/div)
0A
Time (100μs/div)
VEN/SET
(2V/div)
VF
(1V/div)
IIN
(400mA/div)
0V
0V
0A
Time (100μs/div)
Turn-Off from 2x Mode Flash
Backlight Operating Characteristics
(VIN = 2.8V; 151mA/Channel)
(VIN = 3.6V; 1.5x Mode; 30mA/Channel; AC Coupled)
VIN
(20mV/div)
0V
VOUT
(50mV/div)
0V
VBLX
(50mV/div)
0A
Time (100μs/div)
Time (1μs/div)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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7
DATA SHEET
AAT2848
High Current Charge Pump For Backlight Display and Flash Applications
Typical Characteristics
Backlight Operating Characteristics
Flash Operating Characteristics
(VIN = 3.6V; 1.5x Mode; 15mA/Channel; AC Coupled)
(VIN = 3.6V; 1.5x Mode; 151mA/Channel; AC Coupled)
VIN
(20mV/div)
VIN
(20mV/div)
VOUT
(50mV/div)
VOUT
(50mV/div)
VBLX
(50mV/div)
VFLX
(50mV/div)
Time (1μs/div)
Time (1μs/div)
Flash Operating Characteristics
(VIN = 3.3V; 1.5x Mode; 70mA/Channel; AC Coupled)
VIN
(20mV/div)
VOUT
(50mV/div)
VFLX
(50mV/div)
Time (1μs/div)
8
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202069A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012
DATA SHEET
AAT2848
High Current Charge Pump For Backlight Display and Flash Applications
Functional Block Diagram
IN
C1+
C1C2+
C2-
Tri-Mode
Charge Pump
1x/1.5x/2x
BENS
32-Step S2Cwire
Backlight Control
FENS
16-Step S2Cwire
Flash Control
OUT
BL1
BL2
BL3
BL4
Control
Logic
BSET
FL1
FSET
FL2
FADE
FLTMR
PGND
Functional Description
The AAT2848 is an integrated solution for LCD display
applications with a built-in four-channel, 30mA driver for
white LED backlight and two 300mA drivers for flash
LEDs.
The backlight driver uses a dual-mode load switch (1x)
and high-efficiency (1.5x) charge-pump engine. To maximize power conversion efficiency, an internal sensing
circuit monitors the voltage required on each constant
current sink output and sets the load switch and charge
pump mode based on the input battery voltage and the
current sink input voltage. As the battery discharges
over time, the charge pump is enabled when any of the
four current sink inputs nears dropout. The charge pump
operates in 1.5x mode for backlight operation. The
charge pump requires only four external components:
two 1μF ceramic capacitors for the charge pump flying
capacitors (C1 and C2), one 4.7μF ceramic input capacitor (CIN) and one 2.2μF ceramic charge pump output
capacitor (COUT).
The four constant current sink inputs (BL1 to BL4) can
drive up to four individual LEDs with a maximum current
of 30mA each. Because the inputs BL1 to BL4 are true
independent constant current sinks, the voltage observed
on any single given input will be determined by the difference between VOUT and the actual forward voltage (VF)
of the LED being driven.
AGND
Any unused sink inputs must be connected to the OUT
pin; otherwise, the AAT2848 will operate in 1.5x charge
pump mode regardless of the battery voltage or the VF of
the diodes connected to the remaining current sinks. The
S2Cwire serial interface at the BENS input enables the
charge pump and sets the backlight current sink level.
Since the current level is programmable, no PWM (pulse
width modulation) or additional control circuitry is needed
to control LED brightness. This feature greatly reduces
the burden on a microcontroller or system IC to manage
LED or display brightness, allowing the user to “set it, and
forget it.” With its high speed serial interface (>1MHz data
rate), the LED current drive can be changed successively
to brighten or dim the LEDs in smooth transitions or in
abrupt steps, giving the user complete programmability
and real-time control of LED brightness.
The flash driver uses a tri-mode load switch (1x) and
high-efficiency (1.5x and 2x) charge-pump engine. To
maximize power conversion efficiency, an internal sensing circuit monitors the voltage required on each constant flash current sink/channel input and sets the load
switch and charge pump mode based on the input battery voltage and the flash current sink input voltage. As
the battery discharges over time, the charge pump is
enabled when any of the two flash current sink inputs
nears dropout. The charge pump initially starts in 1.5x
mode, and then transitions into 2x mode if the flash current sink inputs nears dropout.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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9
DATA SHEET
AAT2848
High Current Charge Pump For Backlight Display and Flash Applications
Any unused flash sink inputs must be connected to the
OUT pin; otherwise, the AAT2848 will operate continuously in 2x charge pump mode regardless of the battery
voltage or VF of the remaining diodes connected to the
current sinks. The S2Cwire serial interface at the FENS
input enables the charge pump and sets the flash current sink levels.
The backlight and flash LED currents are controlled by a
combination of an external programming resistor from
BSET (for backlight) or FSET (for flash) to AGND and the
backlight or flash serial S2Cwire interface BENS or FENS.
The programming resistor sets the maximum LED current for each channel, and the serial S2Cwire interface
controls the LED current relative to the maximum.
For backlight LEDs, the maximum channel current can
be set up to 30mA with a 10k resistor connected at the
BSET pin of the AAT2848. Depending upon the application and the white LEDs chosen, the preferred and most
accurate method for a backlight LED current control is to
choose RBSET for the maximum backlight current required
by the application conditions and use the S2Cwire control
to set the backlight current to lower levels. The 32 levels
provided by the interface allows a smooth transition
between intermediate values. Table 1 and Figure 1 illustrate the current magnitude control from the S2Cwire
interface at the BENS pin, based on the maximum current set by the RBSET resistor.
For flash white LEDs, the maximum channel current can
be set up to 300mA with a 9.53k resistor connected at
the FSET pin of the AAT2848. Depending upon the application and the flash white LEDs chosen, the preferred
method for flash LED current control is to choose RFSET for
the maximum flash current required by the application
conditions; use the S2Cwire control to set the backlight
current to lower levels. Table 2 and Figure 2 illustrate the
current magnitude control from the S2Cwire interface at
the FENS pin, based on the maximum current set by the
RFSET resistor.
10
BENS Data
IBLX (%)
RBSET (Ω)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
100
97
93
90
87
83
80
77
73
70
67
63
60
57
54
51
47
44
41
38
35
32
28
25
22
19
16
13
10
7
3
1.5
15k
(20mA Max)
Table 1: IBLX (%) vs. BENS Data.
24
BLX Pin Current (mA)
The two constant flash current sink outputs (FL1 and
FL2) can drive up to two LEDs with a maximum current
of 300mA each. Because the outputs FL1 and FL2 are
true independent constant flash current sinks, the voltage observed on any single given output will be determined by the difference between VOUT and the actual
forward voltage (VF) of the flash LED being driven.
RBSET = 15kΩ
20
16
12
8
4
0
1
3
5
7
9
11 13 15 17 19 21 23 25 27 29 31
BENS Data (#)
Figure 1: BL1-BL4 Current Control Profile.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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DATA SHEET
AAT2848
High Current Charge Pump For Backlight Display and Flash Applications
FENS
Data
IFLX
(%)
1
2
3
4
5
6
7
8
100
94
87
81
73
67
60
53
RFSET
(Ω)
FENS
Data
IFLX
(%)
RFSET
(Ω)
14.3k
(206mA
Max)
9
10
11
12
13
14
15
16
46
40
34
27
20
13
6
3
14.3k
(206mA
Max)
FLX Pin Current (mA)
RFSET = 14.3kΩ
200
160
120
80
40
0
1
3
5
7
9
11
13
The flash has 16 current level settings; again, each step
as a percentage of the maximum flash current set by the
FSET resistor.
Flash Timeout Functionality
Table 2: IFLX (%) vs. FENS Data.
240
The AAT2848 features separate control interfaces for
backlight and flash current control. The backlight current
features 32 current steps, each step as a percentage of
the maximum backlight current set by the BSET resistor.
15
The AAT2848 contains an internal flash mode operation
timeout safety circuit. The purpose of this timeout circuit
is to prevent any thermal damage to the flash white LED
when flash mode operation is unable to be disabled by
the embedded microprocessor/microcontroller.
Flash
mode operation is initiated by strobing the FENS pin lowto-high, this also initiates the flash timer circuit which
can be programmed via an external capacitor at the
FLTMR pin. The flash timeout period can be calculated
using the following equation:
Flash Timeout = 3.9 s/μF · CFLTMR
FENS Data (#)
Figure 2: FL1-FL2 Current Control Profile.
S2Cwire Serial Interface
The S2Cwire single-wire serial interface used in the
AAT2848 exhibits flexible timing in that data can be
clocked-in at speeds ranging from 15kHz to higher than
1MHz.
The S2Cwire serial interface recognizes rising edges at
both the BENS pin and at the FENS pin. For setting the
backlight current level, data applied at the AAT2848’s
BENS input is decoded into 32 different levels. For setting the flash current level, data applied at the AAT2848’s
FENS input is decoded into 16 different levels. After data
is supplied, the BENS and the FENS inputs pins are held
high to latch the data.
Once the data at BENS or FENS has been held in the
logic high state for longer than tLAT (500μs), the programmed backlight or flash current becomes active and
the internal backlight and flash data registers are
latched. To adjust the backlight and/or flash current levels once programmed, the requisite number of rising
edges corresponding to the desired code must be applied
at the BENS or the FENS pin.
where Flash Timeout is in seconds and CFLTMR is in μF. For
example, for a 0.33μF capacitor:
Flash Timeout = 3.9 s/μF · 0.33μF = 1.3s
To disable the flash timer, connect the FLTMR pin to
AGND.
When both the BENS and the FENS inputs are strobed
and held low for longer than tOFF (500μs), the AAT2848
enters shutdown mode and draws less than 1μA from
VIN. Both internal backlight and flash data registers are
cleared to zero when in shutdown.
Backlight/Flash LED Current Setting
The maximum backlight and flash LED currents are set,
or programmed, with external resistors. The backlight
LED current is programmed by the RBSET resistor with the
following equation:
RBSET =
300
IBLED
RBSET = Backlight LED Current Programming Resistor
IBLED = Backlight LED Current
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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11
DATA SHEET
AAT2848
High Current Charge Pump For Backlight Display and Flash Applications
t HI
t LO
t OFF
t LAT
BENS/FENS
1
2
n-1
n 32/16
0
Data Reg
n-1
0
Figure 3: S2Cwire Serial Interface Timing.
The flash LED current is programmed by the RFSET resistor with the following equation:
RFSET =
2880
IFLED
RFSET = Flash LED Current Programming Resistor
IFLED = Flash LED Current
Backlight Fade-In/
Fade-Out Functionality
The AAT2848 contains internal circuitry that automates
fade-in/fade-out operation. Fade functionality simply
allows for the turning off/on of the LEDs in a smooth
controlled transition. The AAT2848 does not have to be
manually programmed to avoid the abrupt changes in
lighting when white LED drivers are shutdown/turned-off.
The fade-in/fade-out operation occurs only during device
on/off transitions. The response time is constant regardless of the LED current level.
To disable the fade-in/fade-out timer, connect the FADE
pin to IN.
Auto Disable Feature
The charge pump in AAT2848 is equipped with an autodisable feature for each LED channel. After the IC is
enabled and started up, a test current of 1.5mA (typical)
is forced through each sink channel. The channel will be
disabled if the voltage of that particular BLX or FLX pin
does not drop to a certain threshold. This feature is convenient for disabling an unused channel or during a
flash/backlight LED failed short event.
Thermal Protection
The charge pump has a built-in thermal protection circuit that will shut down the charge pump if the die temperature rises above the thermal limit as is the case
during a short circuit of the OUT pin.
The backlight fade-in/fade-out response time (tFADE) can
be calculated using the following equation:
tFADE = 57 s/μF · CFADE
where tFADE is in seconds and CFADE is in μF. For example,
for a 0.047μF capacitor:
tFADE = 57 s/μF · 0.047μF = 2.7s
12
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202069A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012
DATA SHEET
AAT2848
High Current Charge Pump For Backlight Display and Flash Applications
Applications Information
LED Selection
The AAT2848 is specifically intended for driving white
LEDs. However, the device design will allow the AAT2848
to drive most types of LEDs. LED applications may include
mixed arrangements for display backlighting, color (RGB)
LEDs, infrared (IR) diodes and any other load needing a
constant current source generated from a varying input
voltage. Since the BL1 to BL4 and FL1 to FL2 constant current sinks are matched with negligible voltage dependence, the constant current channels will be matched
regardless of the specific LED forward voltage (VF) levels.
The low-dropout current sinks in the AAT2848 maximize
performance and make it capable of driving LEDs with
high forward voltages. Multiple channels can be combined to obtain a higher LED drive current without complication.
Device Switching Noise Performance
The AAT2848 operates at a fixed frequency of approximately 1MHz to control noise and limit harmonics that
can interfere with the RF operation of cellular telephone
handsets or other communication devices. Back-injected
noise appearing on the input pin of the charge pump is
20mV peak-to-peak, typically ten times less than inductor-based DC/DC boost converter white LED backlight
solutions. The AAT2848 soft-start feature prevents noise
transient effects associated with in-rush currents during
the start up of the charge pump circuit.
Power Efficiency and Device Evaluation
Charge-pump efficiency discussion in the following sections accounts only for the efficiency of the charge pump
section itself. Due to the unique circuit architecture and
design of the AAT2848, it is very difficult to measure
efficiency in terms of a percent value comparing input
power over output power.
Since the AAT2848 outputs are pure constant current
sinks/channels and typically drive individual loads, it is
difficult to measure the output voltage for a given output
(BL1 to BL4 and FL1 to FL2) to derive an overall output
power measurement. For any given application, white
LED forward voltage levels can differ, yet the output
drive current will be maintained as a constant.
This makes quantifying output power a difficult task
when taken in the context of comparing to other white
LED driver circuit topologies. A better way to quantify
total device efficiency is to observe the total input power
to the device for a given LED current drive level. The
best white LED driver for a given application should be
based on trade-offs of size, external component count,
reliability, operating range and total energy usage...not
just "% efficiency."
Device Power Efficiency
The AAT2848’s backlight charge pump conversion efficiency is defined as the power delivered to the white LED
load divided by the input power:
η=
PLEDs VLED1 · ILED1 + ... + VLEDX · ILEDX
=
PIN
VIN · IIN
VLEDx = White LED Forward Voltage (VF)
ILEDx = White LED Bias Current (ID)
X = Number of Backlight White LEDs
The expression to define the estimated ideal backlight
efficiency (η) for the AAT2848 in 1x mode is as follows:
η=
PLEDs VLED1 · ILED1 + ... + VLEDX · ILEDX
=
PIN
VIN · IIN
η=
X · VLEDX · ILEDX
; X = 1, 2, 3 or 4 and IIN = X · ILEDX
VIN · IIN
VLEDX
η= V
IN
The AAT2848’s backlight charge pump is a fractional
charge pump which will boost the input supply voltage in
the event where VIN is less then the required output voltage across the backlight white LED load.
With an ideal 1.5x charge pump, the input current is
1.5x of the output current. The expression to define the
estimated ideal backlight efficiency (η) for the AAT2848
in 1.5x mode is as follows:
η=
PLEDs VLED1 · ILED1 + ... + VLEDX · ILEDX
=
PIN
VIN · IIN
η=
X · VLEDX · ILEDX
; X = 1, 2, 3 or 4 and IIN = 1.5(X · ILEDX)
VIN · IIN
VLEDX
η = 1.5V
IN
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202069A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012
13
DATA SHEET
AAT2848
High Current Charge Pump For Backlight Display and Flash Applications
The AAT2848’s flash charge pump conversion efficiency
is defined as the power delivered to the flash white LED
load divided by the input power:
η=
PLEDs VLED1 · ILED1 + VLED2 · ILED2
=
PIN
VIN · IIN
VLEDx = White LED Forward Voltage (VF)
ILEDx = White LED Bias Current (ID)
X = Number of Flash White LEDs
The expression to define the estimated ideal flash efficiency (η) for the AAT2848 in 1x mode is as follows:
η=
PLEDs VLED1 · ILED1 + VLED2 · ILED2
=
PIN
VIN · IIN
η=
X · VLEDX · ILEDX
; X = 1 or 2 and IIN = X · ILEDX
VIN · IIN
VLEDX
η= V
IN
The AAT2848’s flash charge pump is a fractional charge
pump which will boost the input supply voltage in the
event where VIN is less then the required output voltage
across the flash white LED load.
With an ideal 1.5x charge pump, the input current is
1.5x of the output current. The expression to define the
estimated ideal flash efficiency (η) for the AAT2848 in
1.5x mode is as follows:
η=
PLEDs VLED1 · ILED1 + VLED2 · ILED2
=
PIN
VIN · IIN
η=
X · VLEDX · ILEDX
; X = 1 or 2 and IIN = 1.5(X · ILEDX)
VIN · IIN
VLEDX
η = 1.5V
IN
The same calculations apply for the AAT2848 in 2x mode
where for an ideal 2x charge pump, the input current is
2x of the output current. The expression for the estimated ideal flash efficiency (η) for the AAT2848 in 2x
mode is as follows:
η=
PLEDs VLED1 · ILED1 + VLED2 · ILED2
=
PIN
VIN · IIN
η=
X · VLEDX · ILEDX
; X = 1 or 2 and IIN = 2(X · ILEDX)
VIN · IIN
VLEDX
η = 2V
IN
14
Capacitor Selection
Careful selection of the four most critical external capacitors CIN, C1, C2, and COUT are important because they
will affect turn on time, output ripple and transient performance (the flash timeout and fade functionality
capacitors are not as critical to the normal operation of
the AAT2848). Optimum performance will be obtained
when low ESR (
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