AAT2848IDG-T1 [ANALOGICTECH]
High-Current Charge Pump For Backlight Display and Flash Applications; 大电流电荷泵，用于背光显示和Flash应用程序
| 型号： | AAT2848IDG-T1 |
| 厂家： | 
ADVANCED ANALOGIC TECHNOLOGIES |
| 描述： | High-Current Charge Pump For Backlight Display and Flash Applications |
| 文件： | 总19页 (文件大小：2625K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
PRODUCT DATASHEET
AAT2848
TM
ChargePump
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.
• 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
Each backlight channel can drive up to 30mA, while each
flash current sink/channel can drive up to 300mA (600mA
total). Two independent S2Cwire™ (AnalogicTech’s 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 full-
scale 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 exter-
nal capacitor.
• Built-In Thermal Protection
• Automatic Soft-Start
• -40°C to +85°C Temperature Range
• Available in TQFN33-20 Package
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.
Applications
• Camera Enabled Mobile Devices
• Digital Still Cameras
The AAT2848 is equipped with built-in short-circuit and
over-temperature protection. The soft-start circuitry pre-
vents 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.
• Multimedia Mobile Phones
Typical Application
C1
1μF
C2
1μF
WLEDs
OSRAM LW M673
or equivalent
C1+
C1-
C2- C2+
OUT
IN
Flash LEDs
Lumileds PWF1
COUT
VBAT
CIN
4.7μF
or equivalent
2.2μF
AAT2848
BL1
S2Cwire
BL2
BL3
BL4
BENS
FENS
Backlight Control
S2Cwire
Flash Control
FL1
FL2
BSET
FSET
RBSET
15k
RFSET
14.3k
FLTMR
FADE
AGND
CFLTMR
330nF
CFADE
47nF
PGND
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2848.2008.05.1.0
1
PRODUCT DATASHEET
AAT2848
TM
ChargePump
High-Current Charge Pump For Backlight Display and Flash Applications
Pin Descriptions
Pin # Symbol
Description
Charge pump output; supplies current to the backlight and flash LEDs. Connect the backlight and flash LED an-
odes to OUT. Bypass OUT to PGND with a 2.2μF or larger ceramic capacitor as close to the AAT2848 as possible.
1
OUT
2
3
C2+
AGND
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 auto-
matic 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.
4
FADE
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 9.53kΩ resistor from FSET to AGND sets the maximum flash LED current to
300mA per flash output.
Backlight current setting input. A 10kΩ 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.
5
6
FLTMR
BENS
FENS
FSET
BSET
BL1
7
8
9
10
11
12
13
14
15
BL2
BL3
BL4
FL1
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.
FL2
16
17
18
PGND
C2-
C1-
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.
19
IN
20
EP
C1+
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
1
2
3
4
5
15
14
13
12
11
FL2
FL1
BL4
BL3
BL2
OUT
C2+
AGND
FADE
FLTMR
EP
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2848.2008.05.1.0
PRODUCT DATASHEET
AAT2848
TM
ChargePump
High-Current Charge Pump For Backlight Display and Flash Applications
Absolute Maximum Ratings1
Symbol
Description
Value
Units
VN
VN
VN
TJ
TLEAD
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
-0.3 to 6.0
-0.3 to VOUT + 0.3
-0.3 to VIN + 0.3
-40 to 150
V
V
V
°C
°C
Maximum Soldering Temperature (at leads, 10 sec)
300
Thermal Information2, 3, 4
Symbol
Description
Value
Units
PD
θJA
Maximum Power Dissipation
Maximum Thermal Resistance
2.0
50
W
°C/W
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.
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2848.2008.05.1.0
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PRODUCT DATASHEET
AAT2848
TM
ChargePump
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
Conditions
Min Typ Max Units
VIN
IN Operating Voltage Range
2.7
5.5
V
BENS = IN, FENS = AGND, BL1 = BL2 = BL3 = BL4 = OUT
(Excluding LED Current)
600
μA
BENS = IN, FENS = AGND, BL1 = BL2 = BL3 = BL4 = OPEN
(1.5x CP, no load)
BENS = AGND, FENS = IN, FL1 = FL2 = OUT
(Excluding LED Current)
5.5
mA
μA
IIN(Q)
IN Operating Current
600
BENS = AGND, FENS = IN, FL1 = FL2 = OPEN
(2x CP, no load)
BENS = FENS = AGND
5.5
1.0
mA
IIN(SHDN)
TSD
IN Shutdown Current
Thermal Shutdown
μA
°C
°C
140
15
TSD(HYS)
Thermal Shutdown Hysteresis
Charge Pump Section
IOUT(MAX)
CP Maximum Output Current IN = 3V
720
mA
mV
Charge Pump Mode Transition
VIN(TH_H)
BENS = DATA1
100
Hysteresis
Charge Pump Oscillator
Frequency (1.5X mode)
Charge Pump Soft Start Time
fOSC
tSS
TA = 25°C
1.0
MHz
100
μs
BL1-BL4 Backlight LED Outputs
BENS = DATA1; VIN – VF = 1.5V
BENS = DATA32; VIN – VF = 1.5V
BENS = DATA1; VIN – VF = 1.5V
18
20
22
IBL_(MAX)
ΔI(BL_)
BL1-BL4 Current Accuracy
BL1-BL4 Current Matching
mA
%
0.26 0.32 0.39
±3
BL1-BL4 Charge Pump Mode
Transition Threshold
VBL_(TH)
Any backlight current sink/channel BL1, BL2, BL3, BL4
120
mV
FL1-FL2 Flash LED Outputs
IFL_(MAX) FL1-FL2 Current Accuracy
ΔI(FL_)
FENS = DATA1; VIN – VF = 1.5V
FENS = DATA16; VIN – VF = 1.5V
FENS = DATA1; VIN – VF = 1.5V
180
200
220
mA
%
5.66 6.66 7.66
±3
FL1-FL2 Current Matching
FL1-FL2 Charge Pump Mode
Transition Threshold
VFL_(TH)
Any flash current sink/channel FL1, FL2
300
mV
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2848.2008.05.1.0
PRODUCT DATASHEET
AAT2848
TM
ChargePump
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
Conditions
Min Typ Max Units
BENS and FENS Logic Control
VBENS(L)
VFENS(L)
VBENS(H)
VFENS(H)
,
BENS, FENS Input Low Threshold Voltage
BENS, FENS Input High Threshold Voltage
0.4
1
V
,
1.4
-1
V
μA
s
I
BENS, IFENS BENS, FENS Input Leakage Current
VBENS = VFENS = VIN = 5V
BENS Transition High-to-Low or Low-to-
High; DATA1
tFADE
Automatic Fade-In/Out Timer
Automatic Flash Disable Time
BENS, FENS Low Time
2.7
1.3
tFLASH
tBENS(LOW)
tFENS(LOW)
FENS Transition Low-to-High
s
,
0.3
75
μs
tBENS(HI_MIN)
,
Minimum BENS, FENS High Time
Maximum BENS, FENS High Time
BENS, FENS Off Timeout
50
ns
μs
μs
μs
tFENS(HI_MIN)
tBENS(HI_MAX)
tFENS(HI_MAX)
tBENS(OFF)
tFENS(OFF)
tBENS(LAT)
tFENS(LAT)
,
75
,
500
500
,
BENS, FENS Latch Timeout
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2848.2008.05.1.0
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PRODUCT DATASHEET
AAT2848
TM
ChargePump
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
30mA/ch, VF = 3.4V
15mA/ch, VF = 3.2V
7.5mA/ch, VF = 3.0V
90
80
70
60
50
40
30.0
D1
D2
D3
D4
29.5
29.0
-40
-15
10
35
60
85
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
Temperature (°C)
Flash Efficiency vs. Input Voltage
Flash Current Matching vs. Temperature
(VIN = 3.6V; 150mA/Channel)
100
90
80
70
60
50
40
152
151
150
149
151mA/ch, VF = 3.0V
70mA/ch, VF = 2.9V
148
D1
D2
147
-40
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
-15
10
35
60
85
Input Voltage (V)
Temperature (°C)
Turn-On to 1x Mode Backlight
Turn-On to 1.5x Mode Backlight
(VIN = 4.5V; 30mA/Channel)
(VIN = 3.6V; 30mA/Channel)
VEN/SET
(2V/div)
VEN/SET
(2V/div)
0V
0V
VOUT
VOUT
(2V/div)
(2V/div)
0V
0V
0V
0V
VBLX
(2V/div)
VBLX
(2V/div)
IIN
IIN
0A
0A
(200mA/div)
(200mA/div)
Time (100μs/div)
Time (100μs/div)
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2848.2008.05.1.0
PRODUCT DATASHEET
AAT2848
TM
ChargePump
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)
VEN/SET
(2V/div)
0V
0V
VOUT
VOUT
(2V/div)
(2V/div)
0V
0V
0V
0V
VFLX
(2V/div)
VFLX
(2V/div)
IIN
IIN
0A
0A
(400mA/div)
(400mA/div)
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
VEN/SET
(2V/div)
(2V/div)
0V
0V
0V
0V
VF
(1V/div)
VF
(1V/div)
IIN
IIN
0A
(200mA/div)
0A
(400mA/div)
Time (100μs/div)
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)
VEN/SET
(2V/div)
VIN
(20mV/div)
0V
VF
VOUT
(1V/div)
(50mV/div)
0V
0A
VBLX
(50mV/div)
IIN
(400mA/div)
Time (100μs/div)
Time (1μs/div)
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2848.2008.05.1.0
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PRODUCT DATASHEET
AAT2848
TM
ChargePump
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)
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2848.2008.05.1.0
PRODUCT DATASHEET
AAT2848
TM
ChargePump
High-Current Charge Pump For Backlight Display and Flash Applications
Functional Block Diagram
IN
C1+
C1-
C2+
C2-
Tri-Mode
Charge Pump
1x/1.5x/2x
OUT
BL1
BL2
BL3
BL4
32-Step S2Cwire
Backlight Control
BENS
16-Step S2Cwire
Flash Control
Control
Logic
FENS
BSET
FL1
FL2
FSET
FADE
FLTMR
PGND
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.
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 max-
imize 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 capaci-
tor (CIN) and one 2.2μF ceramic charge pump output
capacitor (COUT).
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 sens-
ing circuit monitors the voltage required on each con-
stant flash current sink/channel input and sets the load
switch and charge pump mode based on the input bat-
tery 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 cur-
rent sink inputs nears dropout.
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 dif-
ference between VOUT and the actual forward voltage (VF)
of the LED being driven.
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PRODUCT DATASHEET
AAT2848
TM
ChargePump
High-Current Charge Pump For Backlight Display and Flash Applications
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 volt-
age observed on any single given output will be deter-
mined by the difference between VOUT and the actual
forward voltage (VF) of the flash LED being driven.
BENS Data
IBLX (%)
RBSET (Ω)
1
2
3
4
5
6
7
8
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
Any unused flash sink inputs must be connected to the
OUT pin; otherwise, the AAT2848 will operate continu-
ously 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 cur-
rent sink levels.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
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 cur-
rent for each channel, and the serial S2Cwire interface
controls the LED current relative to the maximum.
15k
(20mA Max)
For backlight LEDs, the maximum channel current can
be set up to 30mA with a 10kΩ resistor connected at the
BSET pin of the AAT2848. Depending upon the applica-
tion 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 illus-
trate the current magnitude control from the S2Cwire
interface at the BENS pin, based on the maximum cur-
rent set by the RBSET resistor.
3
1.5
Table 1: IBLX (%) vs. BENS Data.
24
RBSET = 15kΩ
20
16
12
8
For flash white LEDs, the maximum channel current can
be set up to 300mA with a 9.53kΩ resistor connected at
the FSET pin of the AAT2848. Depending upon the appli-
cation 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.
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.
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2848.2008.05.1.0
PRODUCT DATASHEET
AAT2848
TM
ChargePump
High-Current Charge Pump For Backlight Display and Flash Applications
The AAT2848 features separate control interfaces for
FENS
Data
IFLX
(%)
RFSET
(Ω)
FENS
Data
IFLX
(%)
RFSET
(Ω)
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.
1
2
3
4
5
6
7
8
100
94
87
81
73
67
60
53
9
46
40
34
27
20
13
6
10
11
12
13
14
15
16
The flash has 16 current level settings; again, each step
as a percentage of the maximum flash current set by the
FSET resistor.
14.3k
(206mA
Max)
14.3k
(206mA
Max)
Flash Timeout Functionality
3
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
Table 2: IFLX (%) vs. FENS Data.
240
RFSET = 14.3kΩ
200
160
120
80
the embedded microprocessor/microcontroller.
Flash
mode operation is initiated by strobing the FENS pin low-
to-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:
40
0
1
3
5
7
9
11
13
15
Flash Timeout = 3.9 s/μF · CFLTMR
FENS Data (#)
where Flash Timeout is in seconds and CFLTMR is in μF. For
example, for a 0.33μF capacitor:
Figure 2: FL1-FL2 Current Control Profile.
Flash Timeout = 3.9 s/μF · 0.33μF = 1.3s
S2Cwire Serial Interface
To disable the flash timer, connect the FLTMR pin to
AGND.
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.
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.
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 set-
ting 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.
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:
Once the data at BENS or FENS has been held in the
logic high state for longer than tLAT (500μs), the pro-
grammed backlight or flash current becomes active and
the internal backlight and flash data registers are
latched. To adjust the backlight and/or flash current lev-
els once programmed, the requisite number of rising
edges corresponding to the desired code must be applied
at the BENS or the FENS pin.
300
IBLED
RBSET
=
RBSET = Backlight LED Current Programming Resistor
IBLED = Backlight LED Current
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2848.2008.05.1.0
11
PRODUCT DATASHEET
AAT2848
TM
ChargePump
High-Current Charge Pump For Backlight Display and Flash Applications
tHI
tOFF
tLO
tLAT
BENS/FENS
Data Reg
1
2
n-1
n 32/16
0
n-1
0
Figure 3: S2Cwire Serial Interface Timing.
The flash LED current is programmed by the RFSET resis-
tor with the following equation:
To disable the fade-in/fade-out timer, connect the FADE
pin to IN.
2880
IFLED
Auto Disable Feature
RFSET
=
The charge pump in AAT2848 is equipped with an auto-
disable 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 con-
venient for disabling an unused channel or during a
flash/backlight LED failed short event.
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 regard-
less of the LED current level.
Thermal Protection
The charge pump has a built-in thermal protection cir-
cuit that will shut down the charge pump if the die tem-
perature 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
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2848.2008.05.1.0
PRODUCT DATASHEET
AAT2848
TM
ChargePump
High-Current Charge Pump For Backlight Display and Flash Applications
This makes quantifying output power a difficult task
Applications Information
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."
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 cur-
rent sinks are matched with negligible voltage depen-
dence, the constant current channels will be matched
regardless of the specific LED forward voltage (VF) levels.
Device Power Efficiency
The AAT2848’s backlight charge pump conversion effi-
ciency is defined as the power delivered to the white LED
load divided by the input power:
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 com-
bined to obtain a higher LED drive current without com-
plication.
PLEDs VLED1 · ILED1 + ... + VLEDX · ILEDX
η =
=
PIN
VIN · IIN
VLEDx = White LED Forward Voltage (VF)
ILEDx = White LED Bias Current (ID)
X = Number of Backlight White LEDs
Device Switching Noise Performance
The expression to define the estimated ideal backlight
efficiency (η) for the AAT2848 in 1x mode is as follows:
The AAT2848 operates at a fixed frequency of approxi-
mately 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 induc-
tor-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.
PLEDs VLED1 · ILED1 + ... + VLEDX · ILEDX
η =
=
PIN
VIN · IIN
X · VLEDX · I
VIN · IIN
η =
η =
LEDX ; X = 1, 2, 3 or 4 and IIN = X · ILEDX
VLEDX
VIN
Power Efficiency and Device Evaluation
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 volt-
age across the backlight white LED load.
Charge-pump efficiency discussion in the following sec-
tions 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.
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:
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.
PLEDs VLED1 · ILED1 + ... + VLEDX · ILEDX
η =
=
PIN
VIN · IIN
X · VLEDX · I
VIN · IIN
η =
η =
LEDX ; X = 1, 2, 3 or 4 and IIN = 1.5(X · ILEDX
)
VLEDX
1.5VIN
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2848.2008.05.1.0
13
PRODUCT DATASHEET
AAT2848
TM
ChargePump
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:
X · VLEDX · I
VIN · IIN
η =
η =
LEDX ; X = 1 or 2 and IIN = 2(X · ILEDX
)
VLEDX
2VIN
PLEDs VLED1 · ILED1 + VLED2 · ILED2
η =
=
PIN
VIN · IIN
VLEDx = White LED Forward Voltage (VF)
ILEDx = White LED Bias Current (ID)
X = Number of Flash White LEDs
Capacitor Selection
Careful selection of the four most critical external capac-
itors CIN, C1, C2, and COUT are important because they
will affect turn on time, output ripple and transient per-
formance (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 (<100mꢀ) ceramic capacitors are used.
In general, low ESR is defined as a resistance that is less
than 100mꢀ.
The expression to define the estimated ideal flash effi-
ciency (η) for the AAT2848 in 1x mode is as follows:
PLEDs VLED1 · ILED1 + VLED2 · ILED2
η =
η =
η =
=
PIN
VIN · IIN
X · VLEDX · I
VIN · IIN
LEDX ; X = 1 or 2 and IIN = X · ILEDX
X7R and X5R type ceramic capacitors are highly recom-
mended over all other types of capacitors for use with the
AAT2848. For the charge pump section, a 1μF or greater
capacitor is required for the fly (C1 and C2) capacitors.
The required input capacitor (CIN) is 4.7ꢁF or greater and
the required output capacitor (COUT) is 2.2ꢁF or greater.
VLEDX
VIN
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.
Ceramic capacitors offer many advantages over their
tantalum and aluminum electrolytic counterparts. A
ceramic capacitor typically has very low ESR, is lowest
cost, has a smaller printed circuit board (PCB) footprint,
and is non-polarized. Low ESR ceramic capacitors maxi-
mize charge pump transient response.
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:
Before choosing a particular capacitor, verify the capaci-
tor’s performance with the characteristics illustrated in
the component’s data sheet. Performance verification
will help avoid undesirable component related perfor-
mance deficiencies. Suggested typical ceramic capacitor
components for AAT2848 are listed in Table 3.
PLEDs VLED1 · ILED1 + VLED2 · ILED2
η =
=
PIN
VIN · IIN
X · VLEDX · I
VIN · IIN
η =
η =
LEDX ; X = 1 or 2 and IIN = 1.5(X · ILEDX
)
VLEDX
1.5VIN
PCB Layout
To achieve adequate electrical and thermal performance,
careful attention must be given to the PCB layout. In the
worst-case operating condition, the chip must dissipate
considerable power at full load. Adequate heat-sinking
must be achieved to ensure intended operation.
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 esti-
mated ideal flash efficiency (η) for the AAT2848 in 2x
mode is as follows:
Figures 6 and 7 illustrate an example PCB layout (evalu-
ation board). See Figures 4 and 5 for the accompanying
schematic of the evaluation board. The bottom of the
package features an exposed metal pad. The exposed
PLEDs VLED1 · ILED1 + VLED2 · ILED2
η =
=
PIN
VIN · IIN
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14
2848.2008.05.1.0
PRODUCT DATASHEET
AAT2848
TM
ChargePump
High-Current Charge Pump For Backlight Display and Flash Applications
pad acts, thermally, to transfer heat from the chip and,
electrically, as a ground connection.
The chip ground is internally connected to both the
exposed pad and to the AGND and PGND pins. It is good
practice to connect the GND pins to the exposed pad
area with traces.
The junction-to-ambient thermal resistance (θJA) for the
connection can be significantly reduced by following a
couple of important PCB design guidelines. The PCB area
directly underneath the package should be plated so
that the exposed paddle can be mated to the top layer
PCB copper during the reflow process. Multiple copper
plated thru-holes should be used to electrically and ther-
mally connect the top surface pad area to additional
ground plane(s).
The flying capacitors (C1 and C2), input capacitor (C4),
and output capacitor (C5) should be connected as close
as possible to the IC. In addition to the external passive
components being placed as close as possible to the IC,
all traces connecting the AAT2848 should be as short
and wide as possible to minimize path resistance and
potential coupling.
Manufacturer
Part Number
Value
Voltage
Temp. Co.
Case
0603ZD105K
0603ZD225K
1ꢁF
2.2ꢁF
1ꢁF
2.2ꢁF
4.7ꢁF
1ꢁF
10
10
25
16
10
16
10
10
AVX
X5R
0603
C1608X5R1E105K
C1608X5R1C225K
C1608X5R1A475K
GRM188R61C105K
GRM188R61A225K
LMK107BJ475KA
TDK
X5R
0603
Murata
X5R
X5R
0603
0603
2.2ꢁF
4.7ꢁF
Taiyo Yuden
Table 3: Suggested Capacitor Components.
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2848.2008.05.1.0
15
PRODUCT DATASHEET
AAT2848
TM
ChargePump
High-Current Charge Pump For Backlight Display and Flash Applications
DC+
J1
1
2
3
VOUT
D4 D3 D2 D1
D6 D5
U1
AAT2848
R12
0
11
15 14 13 12
R10
15K
10
BL1
16
17
18
19
20
9
8
7
6
PGND
C2-
BSET
FSET
FENS
BENS
R11 14.3K
FEN/SET
BEN/SET
C1-
C2
IN
1µF
C1+
C4
4.7µF
1
2
3
4
5
C3
330nF
1µF
C1
C6
47nF
C5
2.2µF
Figure 4: AAT2848 Evaluation Board Schematic.
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16
2848.2008.05.1.0
PRODUCT DATASHEET
AAT2848
TM
ChargePump
High-Current Charge Pump For Backlight Display and Flash Applications
FEN/SET
BEN/SET
R9
100K
3
3
2
2
1
R7
0
J2
J3
1
R6
0
R8
100K
DC+
DC+
R1 R2 R3 R4
1K 1K 1K 1K
U2
PIC12F675
R5
C8
1
2
3
4
8
7
6
5
VDD
GP5
GP4
GP3
VSS
1µF
330
LED7
GP0
GP1
GP2
DATAB
RED
LIGHT
DATAF
FLASH
Figure 5: AAT2848 Evaluation Board Microcontroller Section Schematic.
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2848.2008.05.1.0
17
PRODUCT DATASHEET
AAT2848
TM
ChargePump
High-Current Charge Pump For Backlight Display and Flash Applications
Figure 6: AAT2848 Evaluation Board Top View Layout.
Figure 7: AAT2848 Evaluation Board Bottom View Layout.
w w w . a n a l o g i c t e c h . c o m
18
2848.2008.05.1.0
PRODUCT DATASHEET
AAT2848
TM
ChargePump
High-Current Charge Pump For Backlight Display and Flash Applications
Ordering Information
Package
Marking1
Part Number (Tape and Reel)2
AAT2848IDG-T1
TQFN33-20
ZPXYY
All AnalogicTech products are offered in Pb-free packaging. The term “Pb-free” means semiconductor
products that are in compliance with current RoHS standards, including the requirement that lead not exceed
0.1% by weight in homogeneous materials. For more information, please visit our website at
http://www.analogictech.com/about/quality.aspx.
Package Information
TQFN33-203
3.00 0.05
1.700 0.050
Index Area
R(5x)
Detail "A"
Top View
(Saw Type)
0.210 0.040
Bottom View
Detail "A"
+ 0.10
-0.00
0.203 REF
0
Side View
All dimensions in millimeters.
1. XYY = assembly and date code.
2. Sample stock is generally held on part numbers listed in BOLD.
3. The leadless package family, which includes QFN, TQFN, DFN, TDFN, and STDFN, has exposed copper (unplated) at the end of the lead terminals due to the manufacturing
process. A solder fillet at the exposed copper edge cannot be guaranteed and is not required to ensure a proper bottom solder connection.
Advanced Analogic Technologies, Inc.
3230 Scott Boulevard, Santa Clara, CA 95054
Phone (408) 737-4600
Fax (408) 737-4611
© Advanced Analogic Technologies, Inc.
AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work rights, or other intellectual
property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice. Except as provided in AnalogicTech’s terms and
conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied warranty relating to the sale and/or use of AnalogicTech products including liability or warranties
relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. In order to minimize risks associated with the customer’s applications, adequate
design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to
support this warranty. Specific testing of all parameters of each device is not necessarily performed. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other
brand and product names appearing in this document are registered trademarks or trademarks of their respective holders.
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2848.2008.05.1.0
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