AAT2856_08 [ANALOGICTECH]
High Current Charge Pump with Dual LDO for Backlight Applications; 高电流电荷泵，带有双LDO ，用于背光应用
| 型号： | AAT2856_08 |
| 厂家： | 
ADVANCED ANALOGIC TECHNOLOGIES |
| 描述： | High Current Charge Pump with Dual LDO for Backlight Applications |
| 文件： | 总18页 (文件大小：399K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
PRODUCT DATASHEET
AAT2856
ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications
General Description
Features
The AAT2856 is a highly integrated charge pump with
dual linear regulators optimized for systems powered
from lithium-ion/polymer batteries. The charge pump
provides power for white LED backlight. Six backlight
LEDs can be driven at up to 30mA. AnalogicTech’s
AS2Cwire™ (Advanced Simple Serial Control™) single-
wire interface is used to enable, disable, and set the
current to one of 32 levels for the backlight. Backlight
current matching is 1% for uniform display brightness.
• Input Voltage Range: 2.7V to 5.5V
• Tri-Mode Charge Pump:
Drives up to Six Backlight LEDs
32 Programmable Backlight Current Settings
Ranging from 115μA to 30mA
▪
▪
2MHz Switching Frequency
• Two Linear Regulators:
▪
200mA Output Current
200mV Dropout Voltage
Output Voltage Adjustable from 1.2V to VBATTERY
Output Auto-Discharge for Fast Shutdown
▪
▪
▪
The AAT2856 offers two high-performance low-noise
MicroPower™ low dropout (LDO) linear regulators. Both
regulators use individual enable inputs and each will
supply up to 200mA load current. LDO ground pin cur-
rent is only 80μA, making the AAT2856 ideal for battery-
operated applications.
▪
Individual LDO Enable Inputs
▪
• Built-In Thermal Protection
• Automatic Soft Start
• -40°C to +85°C Temperature Range
• TQFN44-28 Package
The AAT2856 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.
Applications
• Camera-Enabled Mobile Devices
• Digital Still Cameras
The AAT2856 is available in a Pb-free TQFN44-28 pack-
age and operates over the -40°C to +85°C ambient
temperature range.
• Multimedia Mobile Phones
Typical Application
C2
1μF
C1
1μF
C1+ C1-
IN
C2+ C2-
OUT
VOUT
COUT
2.2μF
CIN
4.7μF
WLEDs
OSRAM LW M673
or equivalent
VBAT
IN
BL1
BL2
BL3
BL4
BL5
BL6
AAT2856
ENABLE/SET
ENS
REF
OUTA
FBA
VOUTA
R2A
CBYP
0.1μF
COUTA
2.2μF
R1A
ENA
EN_LDOA
EN_LDOB
OUTB
FBB
VOUTB
R2B
COUTB
ENB
2.2μF
R1B
AGND
PGND
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PRODUCT DATASHEET
AAT2856
ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications
Pin Descriptions
Pin #
Symbol Description
Backlight LED 3 current sink. 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 2 current sink. 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 1 current sink. BL1 controls the current through backlight LED 1. Connect the cathode of
backlight LED 1 to BL1. If not used, connect BL1 to OUT.
1
BL3
BL2
BL1
2
3
4, 5, 23, 24
6
AGND
REF
Analog ground. Connect AGND to PGND at a single point as close to the AAT2856 as possible.
Reference output. Bypass REF to AGND with a 0.1μF or larger ceramic capacitor.
Feedback input for LDO B. FBB measures the output voltage of LDO B. Connect a resistive voltage di-
vider from the output of LDO B to FBB. FBB feedback regulation voltage is 1.2V.
LDO B regulated voltage output. OUTB is the voltage output of LDO B. Bypass OUTB to AGND with a
2.2μF or larger ceramic capacitor as close to the AAT2856 as possible.
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 AAT2856 as possible.
Feedback input for LDO A. FBA measures the output voltage of LDO A. Connect a resistive voltage di-
vider from the output of LDO A to FBA. FBA feedback regulation voltage is 1.2V.
7
8
FBB
OUTB
IN
9, 18
10
FBA
LDO A regulated voltage output. OUTA is the voltage output of LDO A. Bypass OUTA to AGND with a
2.2μF or larger ceramic capacitor as close to the AAT2856 as possible.
11
OUTA
12
13
C1-
C1+
Negative node of charge pump capacitor 1. Connect the 1μF charge pump capacitor 1 from C1+ to C1-.
Positive node of charge pump capacitor 1. Connect the 1μF charge pump capacitor 1 from C1+ to C1-.
Charge pump output; supplies current to the backlight LEDs. Connect the backlight LED anodes to OUT.
Bypass OUT to PGND with a 2.2μF or larger ceramic capacitor as close to the AAT2856 as possible.
LDO B enable input. ENB turns on or off low dropout regulator B (LDO B). Drive ENB high to turn on LDO
B; drive it low to turn it off.
14, 21, 22
15
OUT
ENB
16
17
19
C2+
C2-
PGND
Positive node of charge pump capacitor 2. Connect the 1μF charge pump capacitor 2 from C2+ to C2-.
Negative node of charge pump capacitor 2. Connect the 1μF charge pump capacitor 2 from C2+ to C2-.
Power ground. Connect AGND to PGND at a single point as close to the AAT2856 as possible.
Backlight enable and serial control input. ENS turns the backlight on/off and is the AS2Cwire input to
serially control the backlightLED brightness.
Backlight LED 6 current sink. BL6 controls the current through backlight LED 6. Connect the cathode of
backlight LED 6 to BL6. If not used, connect BL6 to OUT.
Backlight LED 5 current sink. BL5 controls the current through backlight LED 5. Connect the cathode of
backlight LED 5 to BL5. If not used, connect BL5 to OUT.
LDO A enable input. ENA turns on or off low dropout regulator A (LDO A). Drive ENA high to turn on LDO
A; drive low to turn it off.
Backlight LED 4 current sink. BL4 controls the current through backlight LED 4. Connect the cathode of
backlight LED 4 to BL4. If not used, connect BL4 to OUT.
20
25
26
27
ENS
BL6
BL5
ENA
BL4
28
EP
Exposed paddle (bottom); connect to ground as closely as possible to the device.
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2856.2008.02.1.3
PRODUCT DATASHEET
AAT2856
ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications
Pin Configuration
TQFN44-28
(Top View)
28
27
26
25
24
23
22
1
2
3
4
5
6
7
21
20
19
18
17
16
15
BL3
BL2
BL1
OUT
ENS
PGND
IN
C2-
C2+
ENB
AGND
AGND
REF
FBB
8
9
10
11
12
13
14
Absolute Maximum Ratings1
Symbol
Description
Value
Units
IN, OUT, BL1, BL2, BL3, BL4, BL5, BL6 Voltage to AGND
C1+, C1-, C2+, C2- Voltage to AGND
REF, FBB, OUTA, FBA, OUTB, ENA, ENB, ENS Voltage to AGND
PGND Voltage to AGND
-0.3 to 6.0
-0.3 to VOUT + 0.3
-0.3 to VIN + 0.3
-0.3 to 0.3
V
V
V
V
TJ
TLEAD
Operating Junction Temperature Range
Maximum Soldering Temperature (at leads, 10 sec)
-40 to 150
°C
°C
300
Thermal Information2
Symbol
Description
Maximum Power Dissipation3
Value
Units
PD
2
W
θJA
Maximum Thermal Resistance
50
°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. Mounted on a FR4 circuit board.
3. Derate 6.25 mW/°C above 25°C ambient temperature.
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PRODUCT DATASHEET
AAT2856
ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications
Electrical Characteristics1
VIN = 3.6V; CIN = 4.7μF; COUT = 2.2μF; C1 = C2 = 1μF; 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
1X Mode, 3.0V ≤ VIN ≤ 5.5V, Active,
No Load; ENL = AGND, ENS = IN
1.5X Mode, 3.0V ≤ VIN ≤ 5.5V, Active,
No Load; ENL = AGND, ENS = IN
0.63
1.4
1
IIN(Q)
IN Operating Current
4
mA
2X Mode, 3.0V ≤ VIN ≤ 5.5V, Active,
No Load; ENL = AGND, ENS = IN
2.6
5
IIN(SHDN)
TSD
TSD(HYS)
IN Shutdown Current
Over-Temperature Shutdown Threshold
Over-Temperature Shutdown Hysteresis
ENA = ENB = ENS = AGND
1.0
μA
°C
°C
140
15
Charge Pump Section
IOUT
VIN(TH_H)
fOSC
OUT Maximum Output Current
Charge Pump Mode Hysteresis
Charge Pump Oscillator Frequency
200
500
2
mA
mV
MHz
Address 0, Data 1
TA = 25°C
BL1-BL6 Backlight LED Outputs
Address 0, Data 1; VIN - VF = 1.5V
Address 12, Data 2; VIN - VF = 1.5V
Address 0, Data 1; VIN - VF = 1.5V
18
20
30
22
IBL_(MAX)
BL1-BL6 Maximum Current
mA
ΔI(BL_)
BL1-BL6 Current Matching2
1.0
%
VBL_(TH)
BL1-BL6 Charge Pump Mode Transition Threshold
150
mV
ENS Logic Control
VENS(L)
VENS(H)
IENS
tENS(LOW)
tENS(HI_MIN)
tENS(HI_MIN)
tENS(HI_MAX)
tENS(HI_MAX)
tENS(OFF)
tENS(LAT)
ENS Input Low Threshold
0.4
V
V
μA
μs
ENS Input High Threshold
ENS Input Leakage Current
ENS Serial Interface Low Time
1.4
-1.0
0.3
VENS = VIN = 5V
VIN ≥ 3.3V
1.0
75
,
ENS Serial Interface Minimum High Time
ENS Serial Interface Maximum High Time
50
ns
,
VIN ≥ 3.3V
75
μs
ENS Off Timeout
ENS Serial Interface Latch Timeout
500
500
μs
μs
Linear Regulators
IOUT = 1mA to 200mA
ENA = ENB = IN, ENS = AGND
ENA = IN, ENB = AGND or ENA =
AGND, ENB = IN, ENS = AGND
1.17
200
1.2
125
1.23
200
V
FBA, VFBB Output Voltage Tolerance
V
IIN
IOUTA(MAX)
IOUTB(MAX)
VOUTA(DO)
VOUTB(DO)
Ground Pin Current
90
150
μA
mA
mV
dB
,
OUTA, OUTB Maximum Load Current
OUTA, OUTB Dropout Voltage
OUTA, OUTB Power Supply Rejection Ratio
,
IOUT = 150mA
150
50
300
0.4
PSRRA,
PSRRB
IOUT = 10mA, CREF = 10nF, 1kHz
VEN
ENA, ENB Voltage Low Threshold
ENA, ENB Voltage High Threshold
ENA, ENB Enable Delay
V
V
μs
_
(L)
VEN
tEN
1.4
_
(H)
REF = Open
15
_
(DLY)
1. The AAT2856 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured by design, characterization, and correla-
tion with statistical process controls.
2. Current matching is defined as the deviation of any sink current from the average of all active channels.
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PRODUCT DATASHEET
AAT2856
ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications
Typical Characteristics
Backlight Efficiency vs. Input Voltage
Backlight Current Matching vs. Temperature
(20mA/Ch; Data 1)
100
90
80
70
60
50
40
30
21
20.5
20
20mA/ch
19.5
19
10.2mA/ch
1.6mA/ch
18.5
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
-40
-15
10
35
60
85
Input Voltage (V)
Temperature (°C)
Turn On to 1X Mode Backlight
(30mA/ch; Data 1; VIN = 4.2V)
Turn On to 1.5X Mode Backlight
(30mA/ch; Data 1; VIN = 3.4V)
VEN
(2V/div)
VEN
(2V/div)
0V
0V
0V
VOUT
(2V/div)
VOUT
(2V/div)
0V
0V
VSINK
(500mV/div)
VSINK
(500mV/div)
0V
IIN
(200mA/div)
0A
IIN
(200mA/div)
0A
Time (200µs/div)
Time (200µs/div)
Turn On to 2X Mode Backlight
(30mA/ch; Data 1; VIN = 2.7V)
Turn Off from 1.5X Mode Backlight
(30mA/ch; Data 1)
VEN
(2V/div)
VEN
(2V/div)
0V
0V
0V
VOUT
(2V/div)
VOUT
(2V/div)
VSINK
(500mV/div)
0V
0A
0V
IIN
(200mA/div)
IIN
(200mA/div)
0A
Time (200µs/div)
Time (100µs/div)
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PRODUCT DATASHEET
AAT2856
ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications
Typical Characteristics
BENS, FENS High Threshold Voltage
vs. Input Voltage
BENS, FENS Low Threshold Voltage
vs. Input Voltage
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
-40°C
-40°C
25°C
85°C
85°C
25°C
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
Input Voltage (V)
BENS, FENS Latch Timeout vs. Input Voltage
BENS, FENS Off Timeout vs. Input Voltage
300
260
240
260
220
180
140
100
25°C
220
25°C
-40°C
200
-40°C
180
85°C
160
25°C
140
120
100
80
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
Input Voltage (V)
LDOs A and B Turn On Characteristic
LDOs A and B Load Regulation
1.0
0.5
VEN
(2V/div)
0V
0V
OUTA
OUTB
0.0
VOUT
(500mV/div)
-0.5
-1.0
0.1
1
10
100
1000
Time (50µs/div)
Load Current (mA)
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2856.2008.02.1.3
PRODUCT DATASHEET
AAT2856
ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications
Typical Characteristics
LDOs A and B Line Regulation
LDOs A and B Output Voltage
vs. Temperature
1.5
1
1.0
0.5
0
OUTA
0.5
0
OUTB
-0.5
-1
-0.5
-1.0
-1.5
-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)
LDOs A and B Dropout Characteristics
LDOs A and B Line Transient Response
(10mA Load)
3.2
3.0
2.8
2.6
2.4
2.2
2.0
VIN = 3.6V
IOUT = 100mA
VIN
(250mV/div)
VIN = 3.1V
IOUT = 200mA
VOUT
(AC Coupled)
(20mV/div)
2.7
2.8
2.9
3.0
3.1
3.2
Time (50µs/div)
Input Voltage (V)
LDOs A and B Load Transient Response
(10mA to 200mA Load Step)
IOUT = 200mA
IOUT
(100mA/div)
VOUT
(AC Coupled)
(100mV/div)
Time (50µs/div)
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PRODUCT DATASHEET
AAT2856
ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications
Functional Block Diagram
IN IN
C1+
C1-
OUTA
FBA
1X/1.5X/2X
Tri-mode
Charge Pump
C2+
C2-
VREF
OUTB
FBB
VREF
REF
OUT
ENA
ENB
To LDO A
To LDO B
BL1
BL2
BL3
BL4
Control
Logic
ENS
BL5
BL6
AGND PGND
The charge pump is controlled by the voltage across the
LED current sinks. When any one of the active current
sinks begins to dropout, the charge pump goes to the
next higher mode (from 1X to 1.5X or from 1.5X to 2X
mode) to maintain sufficient LED voltage for constant
LED current. The AAT2856 continuously monitors the
LED forward voltages and uses the input voltage to
determine when to reduce the charge pump mode for
better efficiency. There is also a 500mV mode-transition
hysteresis that prevents the charge pump from oscillat-
ing between charge pump modes.
Functional Description
The AAT2856 is a highly integrated backlight LED driver
with two LDO linear regulators. The charge pump LED
driver drives backlight LEDs from a 2.7V to 5.5V input
voltage. The LDO regulators are operated from the same
input voltage range and produce regulated output volt-
ages as low as 1.2V.
LED Drivers
The LEDs are driven from an internal charge pump that,
depending on the battery voltage and LED forward volt-
age, drives LEDs directly from the supply voltage (1X or
bypass mode) or steps up the supply voltage by a factor
of 1.5 (1.5X mode) or 2 (2X mode). The charge pump
requires only two tiny 1μF ceramic capacitors, providing a
more compact solution than typical inductor-based step-
up converter solutions. Each individual LED is driven by a
current sink to AGND, allowing individual current control
with high accuracy over a wide range of input voltages and
LED forward voltages while maintaining high efficiency.
The backlight LED current levels are dynamically control-
lable by the AS2Cwire single-wire interface. The backlight
section has multiple current level scales and the maxi-
mum current level is fixed at 20mA or 30mA, depending
on the scale chosen through programming.
If any one of the backlight or flash current sinks is not
used, connect that current sink to OUT. The current con-
troller monitors the sink voltage and, if it is connected to
OUT, then the controller determines that the current sink
is not used or that the LED is shorted. In either case, the
controller turns off the affected current sink.
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2856.2008.02.1.3
PRODUCT DATASHEET
AAT2856
ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications
AS2Cwire Serial Interface
AS2Cwire Serial Interface Addressing
The AAT2856 is dynamically programmable by the
AS2Cwire single-wire interface. AS2Cwire records rising
edges detected at the ENS pin to address and load the
data registers. AS2Cwire latches data or address after the
ENS input has been held high for time tLAT (500μs).
Address or data is differentiated by the number of ENS
rising edges. Since the data registers are 4 bits each, the
differentiating number of pulses is 24 or 16, so that
Address 0 is identified by 17 rising edges, Address 1 by
18 rising edges, Address 2 by 19 rising edges, etc. Data
is set to any number of rising edges between 1 and 16. A
typical write protocol is a burst of ENS rising edges iden-
tifying a particular address, followed by a pause with ENS
held high for the tLAT timeout period, then a burst of rising
edges signifying data, and another tLAT timeout after the
data has been sent. Once an address is set, multiple
writes to that address are allowed since the address is not
reset after each write. Address edges are needed when
changing the address, or writing to an address other than
the default after shutdown. Address 0 is the default
address after shutdown. If the part is enabled with only
data edges and no address, then Address 0 will be pro-
grammed and backlight channels BL1-BL6 will turn-on
according to the number of data edges applied.
ENS Rising
Address
Edges
Function
0
1
2
3
17
18
19
20
Backlight Current BL1-BL6
Main Backlight Current BL1-BL5
Sub Backlight Current BL6
Low Current Backlight
Maximum Backlight Current
Scale BL1-BL6
12
15
29
32
Backlight Independent Channel
Control
Table 1a: AS2Cwire Serial Interface Addressing
with Independent Channel Control Disabled.
ENS Rising
Address
Edges
Function
0
1
2
3
17
18
19
20
Not Applicable
Backlight Current BL1-BL6
BL3-BL6 On/Off Control
BL1-BL2 On/Off Control
Maximum Backlight Current
Scale BL1-BL6
12
15
29
32
Not Applicable
Table 1b: AS2Cwire Serial Interface Addressing
with Independent Channel Control Enabled.
When ENS is held low for a time longer than tOFF (500μs),
the AAT2856 enters shutdown mode and draws less than
1μA of current from IN. At shutdown, the data and
address registers are reset to 0.
Backlight Current Control (Address 0-3)
Use Addresses 0-3 to program all six backlight LED
channels. All six backlight channels are programmed to
the same current level by writing Address 0 followed by
any Data between 1 and 16. To program only the main
channels BL1 through BL5, use Address 1. Similarly,
use Address 2 to program only the sub channel BL6
independently.
Table 1a contains the AS2Cwire serial interface address
functionality when independent channel control is dis-
abled (independent channel control is disabled by
default) and conversely Table 1b contains the AS2Cwire
serial interface address functionality when independent
channel control is enabled.
Address
Data
THI
TLAT
TLO
TLAT
EN/SET
1
2
17
18
1
2 . . .
n <= 16
0
Address
Data Reg 1
Data Reg 2
1
0
0
n
Figure 1: AS2Cwire Serial Interface Timing.
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2856.2008.02.1.3
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PRODUCT DATASHEET
AAT2856
ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications
The AAT2856 incorporates additional circuitry that opti-
35
mizes performance for exceptionally low backlight cur-
rent settings. A separate address is used to activate this
30
30mA FS
25
circuitry. To program the low current settings with
20
improved performance and efficiency, write to Address
3. Unlike Addresses 0-2, which have current level set-
15
20mA FS
10
tings according to Table 2 and Figure 2, Address 3 pos-
5
sesses a separate set of current levels described by the
Low Current Backlight settings found in Table 3.
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16
Data Code
Data
30mA Max (mA)
20mA Max (mA)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
30.0
27.9
26.1
24.2
21.0
19.2
17.3
15.0
12.7
10.9
8.1
20.0
19.0
17.8
16.5
14.3
13.0
11.8
10.2
8.5
7.3
5.4
4.1
2.9
Figure 2: Data Code for Address 0-3 vs.
Backlight Current Level.
Maximum Backlight Current
(Address 12)
There are two separate current level scales that apply to
Addresses 0-2: 20mA and 30mA. According to the
Maximum Backlight Current setting at Address 12, only
one of the two scales can be active at any given time
and never both. By default, the 20mA scale is active on
startup. To change to the 30mA scale, or go back to the
20mA scale, write to Address 12.
6.2
4.4
3.5
2.6
2.2
1.6
0
0
Since only one of the scales can be active at any given
time, the 20mA and 30mA scales cannot be mixed
between main and sub. When setting Address 12 to the
30mA scale, only current levels from that scale can be
mixed between main and sub. When changing maximum
current scales, the data remains constant regardless of
scale. When the maximum current scale is changed, the
previously stored data value will remain constant but the
current value will change due to the different current
values on the separate maximum current scales.
Table 2: Data for the Backlight Current Level,
Addresses 0-3.
Main Current
On
Sub Current
On
Current
(μA)
Data
1
2
No
No
No
No
0
0
3
No
No
0
4
No
No
0
5
6
7
8
No
No
No
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
No
No
No
Yes
Yes
Yes
Yes
95
Data
Maximum Current Scale
500
950
1900
95
500
950
1900
95
1
2
20mA
30mA
9
Table 4: Address 12 Maximum Current Scale.
10
11
12
13
14
15
16
Backlight Independent Channel Control
(Address 15)
500
950
1900
The AAT2856 has a unique independent channel control
mode whereby individual backlight LED channels can be
enabled and disabled to form a custom arrangement of
active channels.
Table 3: Low-Level Backlight Current,
Address 3, FS = 20mA Range.
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2856.2008.02.1.3
PRODUCT DATASHEET
AAT2856
ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications
To enable independent channel control mode, write Data
Data
BL2
BL1
8 to Address 15. To exit individual mode control, the
AAT2856 state machine can be reset by strobing ENS
low and holding ENS low longer than the AS2Cwire’s tOFF
latch time.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Off
Off
Off
Off
Off
Off
Off
Off
On
On
On
On
On
On
On
On
Off
Off
Off
Off
On
On
On
On
Off
Off
Off
Off
On
On
On
On
Data
Individual Backlight Control
8
On
Table 5: Address 15, Independent
Backlight Control.
With independent channel control enabled, the functional-
ity of Addresses 2 and 3 will conform to what is described
in Tables 8 and 9. Also Address 0 is no longer applicable
after independent channel control has been enabled. As
indicated by the possible settings listed in the tables, any
combination of backlight channels can be enabled and
disabled. The original functionality (Sub Backlight Current
BL6 and Low Current Backlight) of Addresses 2 and 3 are
no longer available unless the internal state machine has
been reset to default mode operation (when ENS is logic
low for >500μs). The functionality of the maximum back-
light current scale (Address 12) is unmodified by the
enabling of independent channel control.
Table 7: Address 3 with Independent Channel
Control Enabled: BL1 and BL2 On/Off Control.
Low Dropout Regulators
The AAT2856 includes two independent LDO linear regu-
lators. The regulators operate from a 2.7V to 5.5V input
voltage at IN. The AAT2856 supplies separate LDO
enable inputs (ENA and ENB) to control individually the
operation of the LDOs. The LDO output voltages are set
through resistive voltage dividers from the output (OUTA
or OUTB) to the feedback input (FBA or FBB). The regu-
lator controls the output voltage such that the voltage
divider output is at the 1.2V feedback threshold. The low
200mV dropout voltage at 200mA load current allows
the regulator to maintain output voltage regulation.
The LDO enables are always independent of AS2Cwire
programming.
Data
BL6
BL5
BL4
BL3
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Off
Off
Off
Off
Off
Off
Off
Off
On
On
On
On
On
On
On
On
Off
Off
Off
Off
On
On
On
On
Off
Off
Off
Off
On
On
On
On
Off
Off
On
On
Off
Off
On
On
Off
Off
On
On
Off
Off
On
On
Off
On
Off
On
Off
On
Off
On
Off
On
Off
On
Off
On
Off
On
Each LDO regulator can supply up to 200mA continuous
current to the load. They include current limiting and
thermal overload protection to prevent damage to the
load or to the LDOs.
Table 6: Address 2 with Independent Channel
Control Enabled: BL3-BL6 On/Off Control.
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2856.2008.02.1.3
11
PRODUCT DATASHEET
AAT2856
ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications
Applications Information
R2 Standard 1% Values (R1 = 120K)
VOUT (V)
R2 (Ω)
LDO Output Voltage Programming
2.8
2.5
2.0
1.8
1.5
160K
130K
79.6K
60.4K
30.1K
The output voltages for LDOA and LDOB are programmed
by an external resistor divider network. As shown below,
the selection of R1 and R2 is a straight forward matter.
R1 is chosen by considering the tradeoff between the
feedback network bias current and resistor value. Higher
resistor values allow stray capacitance to become a
larger factor in circuit performance whereas lower resis-
tor values increase bias current and decrease efficiency.
Table 8: Example Output Voltages and
Corresponding Resistor Values.
Device Power Efficiency
OUT(A/B)
VOUT(A/B)
The AAT2856 power conversion efficiency depends on
the charge pump mode. By definition, device efficiency
is expressed as the output power delivered to the LEDs
divided by the total input power consumed.
R2(A/B)
R1(A/B)
FB(A/B)
VREF(A/B) = 1.2V
POUT
η =
PIN
When the input voltage is sufficiently greater than the
LED forward voltages, the device optimizes efficiency by
operating in 1X mode. In 1X mode, the device is working
as a bypass switch and passing the input supply directly
to the output. By simplifying the conditions such that the
LEDs have uniform VF, the power conversion efficiency
can be approximated by:
To select appropriate resistor values, first choose R1 such
that the feedback network bias current is less than 10μA.
Then, according to the desired VOUT, calculate R2 according
to the equation below. An example calculation follows.
An R1 value of 120K is chosen, resulting in a small feed-
back network bias current of 1.2V/120K = 10μA. The
desired output voltage is 1.8V. From this information, R2
is calculated from the equation below.
VF · ILED
VIN · IIN
VF
η =
≈
VIN
R1(VOUT - 1.2V)
R2 =
1.2V
Due to the very low 1X mode quiescent current, the input
current nearly equals the total output current delivered
to the LEDs. Further, the low-resistance bypass switch
introduces negligible voltage drop from input to output.
The result is R2 = 60K. Since 60K is not a standard
1%-value, 60.4K is selected. From this example calcula-
tion, for VOUT = 1.8V, use R1 = 120K and R2 = 60.4K.
Example output voltages and corresponding resistor val-
ues are provided in Table 8.
The AAT2856 further maintains optimized performance
and efficiency by detecting when the input voltage is not
sufficient to sustain LED drive current. The device auto-
matically switches to 1.5X mode when the input voltage
drops too low in relation to the LED forward voltages.
Selection of set resistor values outside of the typical
application must be carefully evaluated to ensure that the
application’s performance requirements can still be met.
In 1.5X mode, the output voltage can be boosted to 3/2
the input voltage. The 3/2 conversion ratio introduces a
corresponding 1/2 increase in input current. For ideal
conversion, the 1.5X mode efficiency is given by:
VF · ILED
VF
η =
=
VIN · 1.5IIN 1.5 · VIN
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2856.2008.02.1.3
PRODUCT DATASHEET
AAT2856
ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications
Similarly, when the input falls further, such that 1.5X
mode can no longer sustain LED drive current, the device
Ceramic Capacitor Materials
Ceramic capacitors less than 0.1μF are typically made
will automatically switch to 2X mode. In 2X mode, the
from NPO or C0G materials. NPO and C0G materials
output voltage can be boosted to twice the input voltage.
generally have tight tolerance and are very stable over
The doubling conversion ratio introduces a corresponding
temperature. Larger capacitor values are usually com-
doubling of the input current. For ideal conversion, the
posed of X7R, X5R, Z5U, or Y5V dielectric materials.
2X mode efficiency is given by:
Large ceramic capacitors are often available in lower-
cost dielectrics, but capacitors greater than 10μF are not
VF · ILED
VF
typically required for AAT2856 applications.
η =
=
VIN · 2IIN 2 · VIN
Capacitor area is another contributor to ESR. Capacitors
that are physically larger will have a lower ESR when
compared to an equivalent material smaller capacitor.
These larger devices can improve circuit performance
when compared to an equal value capacitor in a smaller
package size.
LED Selection
The AAT2856 is designed to drive high-intensity white
LEDs. It is particularly suitable for LEDs with an operat-
ing forward voltage in the range of 1.5V to 4.2V.
PCB Layout
The charge pump can also drive other loads that have
similar characteristics to white LEDs. For various load
types, the AAT2856 provides a high-current, program-
mable ideal constant current source.
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.
Capacitor Selection
Careful selection of the four external capacitors CIN, C1,
C2, and COUT is important because they will affect turn-on
time, output ripple, and transient performance. Optimum
performance will be obtained when low equivalent series
resistance (ESR) ceramic capacitors are used. In gen-
eral, low ESR may be defined as less than 100mΩ.
Figure 3 illustrates an example PCB layout. The bottom
of the package features an exposed metal paddle. The
exposed paddle acts, thermally, to transfer heat from
the chip and, electrically, as a ground connection.
The junction-to-ambient thermal resistance (θJA) for the
connection can be significantly reduced by following a
couple of important PCB design guidelines.
Ceramic composition capacitors are highly recommend-
ed over all other types of capacitors for use with the
AAT2856. Ceramic capacitors offer many advantages
over their tantalum and aluminum electrolytic counter-
parts. A ceramic capacitor typically has very low ESR, is
lowest cost, has a smaller PCB footprint, and is non-
polarized. Low ESR ceramic capacitors help maximize
charge pump transient response. Since ceramic capaci-
tors are non-polarized, they are not prone to incorrect
connection damage.
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 re-flow process. Multiple
copper plated thru-holes should be used to electrically
and thermally connect the top surface paddle area to
additional ground plane(s) and/or the bottom layer
ground pour.
The chip ground is internally connected to both the
paddle and to the AGND and PGND pins. It is good prac-
tice to connect the GND pins to the exposed paddle area
with traces as shown in the example.
Equivalent Series Resistance
ESR is an important characteristic to consider when
selecting a capacitor. ESR is a resistance internal to a
capacitor that is caused by the leads, internal connec-
tions, size or area, material composition, and ambient
temperature. Capacitor ESR is typically measured in mil-
liohms for ceramic capacitors and can range to more
than several ohms for tantalum or aluminum electrolytic
capacitors.
The flying capacitors C1 and C2 should be connected
close to the IC. Trace length should be kept short to
minimize path resistance and potential coupling. The
input and output capacitors should also be placed as
close to the chip as possible.
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2856.2008.02.1.3
13
PRODUCT DATASHEET
AAT2856
ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications
supply connection by positioning the J1 jumper to the
ON position. A red LED indicates that power is applied.
The Enables of both LDOs are connected with jumpers J3
and J4. These terminals must be connected to the exter-
nal source to turn on/off the LDOs.
When applying external enable signals, consideration
must be given to the voltage levels. The externally
applied voltages cannot exceed the supply voltage that
is applied to the IN pins of the device (DC+).
The LDO loads can be connected directly to the evalua-
tion board. For adequate performance, be sure to con-
nect the load between OUTA/OUTB and DC- as opposed
to some other GND in the system.
Figure 3: Example PCB Layout.
Button(s)
Pushed
Description
Evaluation Board User Interface
[Push/Release once] Increment the number
of EN/SET edges, but the backlight current
is decreased (dimmer). If held down, auto-
cycle through the settings.
[Push/Release once] Decrement the number
of EN/SET edges, but the backlight current
is increased (brighter). If held down, auto-
cycle through the settings.
The user interface for the AAT2856 evaluation board is
provided through 4 buttons and a number of connection
terminals. The board is operated by supplying external
power and pressing individual buttons or button combi-
nations. The table below indicates the function of each
button or button combination.
SW1
SW2
SW3
[Push/Release once] Toggle between 20mA
and 30mA maximum current.
To power-on the board, connect a power supply or bat-
tery to the DC- and DC+ terminals. Make the board’s
Table 9: AAT2856 Evaluation Board User Interface1.
Evaluation Board Layout
Figure 4: AAT2856 Evaluation Board
Layout Top Side.
Figure 5: AAT2856 Evaluation Board
Layout Bottom Side.
1. The enable for LDOA and LDOB are manually set externally.
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2856.2008.02.1.3
PRODUCT DATASHEET
AAT2856
ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications
Evaluation Board Schematics
DC+
1
2
3
VIN
C12
100μF
100μF (optional)
lab supply bypass
J1
VOUT
C3
2.2μF
D1
D2
D3
D4
D5
D6
J2
0
ENA
U1
AAT2856
28 27 26 25 24 23 22
1
2
3
4
5
6
7
21
BL3
OUT
20
19
18
17
16
15
BL2
BL1
ENS
PGND
IN
ENS
AGND
AGND
REF
C4
4.7μF
C2-
C2
1.0μF
C2+
ENB
C8
0.1μF
FBB
ENB
8
9
10 11 12 13 14
VOUT
OUTB
C5
2.2μF
C1
1.0μF
R2
78.7k
Programmed for
2.8V output by default
C6
2.2μF
R1
59k
OUTA
C7
2.2μF
R4
29.4k
Programmed for
1.8V output by default
R4 (Ω), R3 = 59k
VOUT A/B(V) R2 (Ω), R1 = 59k
R3
59k
1.2
1.8
2.8
1.5
2.5
3.3
R4 short, R5 open (R2 short, R1 open)
29.4K
78.7K
14.7K
63.4K
105K
Figure 6: AAT2856 Section Schematic.
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2856.2008.02.1.3
15
PRODUCT DATASHEET
AAT2856
ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications
U3
VIN
AAT4296
1
2
3
4
8
7
6
5
IN
OUT3
OUT4
OUT5
OUT2
OUT1
C11
0.1μF
EN/SET GND
J3
J4
ENA
ENB
ENA
ENB
R6
100K
(Opt)
R5
100K
(Opt)
VIN
VIN
R8 R9 R10
1K 1K 1K
U2
R7
1
2
3
8
7
6
5
VDD
VSS
GP0
GP1
GP2
C10
1μF
330
GP5
SW1
SW2
SW3
GP4
4
LED7
RED
GP3
PIC12F675
ENS
DC-
Figure 7: MCU and I/O Expander Section Schematic.
Evaluation Board Component Listing
Component
Part#
Description
Manufacturer
U1
U2
U3
AAT2856INJ-EE-T1
PIC12F675
AAT4296IJS-1-T1
LW M673
High Eff. 1X/1.5X/2X CP for White LED, Dual LDO
8-bit CMOS, FLASH MCU; 8-pin PDIP
I/O Expander
AnalogicTech
Microchip
AnalogicTech
OSRAM
D1-D6
C1, C2, C10
C3, C5, C6, C7
C4
Mini TOPLED White LED; SMT
1.0μF, 10V, X5R, 0603, Ceramic
2.2μF, 10V, X5R, 0603, Ceramic
4.7μF, 10V, X5R, 0603, Ceramic
0.1μF, 16V, X7R, 0603, Ceramic
100μF, 10V, 10μA, Tantalum
1K, 5%, 1/4W; 1206
GRM18x
GRM18x
GRM18x
GRM18x
Murata
Murata
Murata
Murata
AVX
Vishay
Vishay
Vishay
C8, C11
C12
R8-R10
R7
R5, R6
R4
R2
R1, R3
J1-J4
LED7
TAJBx
Chip Resistor
Chip Resistor
Chip Resistor
Chip Resistor
Chip Resistor
Chip Resistor
PRPN401PAEN
CMD15-21SRC/TR8
PTS645TL50
330, 5%, 1/4W; 1206
100K, 5%, 1/10W; 0603
29.4K, 1%, 1/10W; 0603
78.7K, 1%, 1/10W; 0603
59K, 1%, 1/10W; 0603
Conn. Header, 2mm Zip
Red LED; 1206
Switch Tact, SPST, 5mm
Vishay
Vishay
Vishay
Sullins Electronics
Chicago Miniature Lamp
ITT Industries
SW1-SW3
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2856.2008.02.1.3
PRODUCT DATASHEET
AAT2856
ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications
Ordering Information
Package
Marking1
Part Number (Tape and Reel)2
AAT2856INJ-EE-T1
TQFN44-28-0.4
YFXYY
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 Information3
TQFN44-28-0.4
Pin 1 Dot
by Marking
Detail "A"
C0.3
4.000 0.050
2.600 0.050
Bottom View
Top View
0.400 0.050
0.430 0.050
0.750 0.050
0.203 REF
0.050 0.050
Side View
Pin 1 Indicator
Detail "A"
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.
w w w . a n a l o g i c t e c h . c o m
2856.2008.02.1.3
17
PRODUCT DATASHEET
AAT2856
ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications
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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