AAT2856INJ-EE-T1 [ANALOGICTECH]
High Current Charge Pump with Dual LDO for BacklightApplications; 高电流电荷泵，带有双LDO的BacklightApplications
| 型号： | AAT2856INJ-EE-T1 |
| 厂家： | 
ADVANCED ANALOGIC TECHNOLOGIES |
| 描述： | High Current Charge Pump with Dual LDO for BacklightApplications |
| 文件： | 总22页 (文件大小：487K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
AAT2856
High Current Charge Pump with
Dual LDO for BacklightApplications
™
ChargePump
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 back-
light. Six backlight LEDs can be driven at up to
•
•
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:
2
30mA. AnalogicTech's AS Cwire™ (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.
•
— 200mA Output Current
— 200mV Dropout Voltage
— Output Voltage Adjustable from 1.2V to
VBATTERY
The AAT2856 offers two high-performance low-
noise MicroPower™ low dropout (LDO) linear regu-
lators. Both regulators use individual enable inputs
and each will supply up to 200mA load current. LDO
ground pin current is only 80µA, making the
AAT2856 ideal for battery-operated applications.
— Output Auto-Discharge for Fast Shutdown
— 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 cir-
cuitry prevents excessive inrush current at start-up
and mode transitions.
Applications
The AAT2856 is available in a Pb-free TQFN44-28
package and operates over the -40°C to +85°C
ambient temperature range.
•
•
•
Camera-Enabled Mobile Devices
Digital Still Cameras
Multimedia Mobile Phones
Typical Application
C2
1μF
C1
1μF
C1+ C1-
IN
C2+ C2-
OUT
VOUT
COUT
2.2μF
CIN
4.7μF
WLEDs
VBAT
IN
OSRAM LW M673
or equivalent
BL1
BL2
BL3
BL4
BL5
BL6
AAT2856
ENABLE/SET
ENS
REF
OUTA
FBA
VOUTA
R2A
R1A
CBYP
0.1μF
COUTA
2.2μF
ENA
ENB
EN_LDOA
EN_LDOB
OUTB
FBB
VOUTB
R2B
R1B
COUTB
2.2μF
AGND
PGND
2856.2007.06.1.0
1
AAT2856
High Current Charge Pump with
Dual LDO for BacklightApplications
Pin Descriptions
Pin #
Symbol
Description
1
BL3
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.
Analog ground. Connect AGND to PGND at a single point as close to the AAT2856 as
possible.
2
BL2
BL1
3
4, 5, 23, 24
AGND
6
7
REF
FBB
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 divider 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 divider from the output of LDO A to FBA. FBA feedback regulation voltage is 1.2V.
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.
Negative node of charge pump capacitor 1. Connect the 1µF charge pump capacitor 1
from C1+ to C1-.
8
9, 18
10
OUTB
IN
FBA
OUTA
C1-
11
12
13
C1+
OUT
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.
14, 21, 22
15
16
17
19
20
25
26
27
28
EP
ENB
C2+
C2-
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.
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 pos-
sible.
PGND
ENS
BL6
Backlight enable and serial control input. ENS turns the backlight on/off and is the
2
AS Cwire 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.
Exposed paddle (bottom); connect to ground as closely as possible to the device.
BL5
ENA
BL4
2
2856.2007.06.1.0
AAT2856
High Current Charge Pump with
Dual LDO for BacklightApplications
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
2856.2007.06.1.0
3
AAT2856
High Current Charge Pump with
Dual LDO for BacklightApplications
1
Absolute Maximum Ratings
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
2
Thermal Information
Symbol
Description
Maximum Power Dissipation
Value
Units
W
3
PD
2
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.
4
2856.2007.06.1.0
AAT2856
High Current Charge Pump with
Dual LDO for BacklightApplications
1, 2
Electrical Characteristics
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
2X Mode, 3.0V ≤ VIN ≤ 5.5V, Active,
No Load; ENL = AGND, ENS = IN
ENA = ENB = ENS = AGND
1
IIN(Q)
IN Operating Current
4
mA
5
IIN(SHDN)
TSD
IN Shutdown Current
Over-Temperature Shutdown
Threshold
Over-Temperature Shutdown
Hysteresis
1.0
µA
°C
140
15
TSD(HYS)
°C
Charge Pump Section
IOUT
OUT Maximum Output Current
200
500
mA
mV
VIN(TH H)
Charge Pump Mode Hysteresis
Charge Pump Oscillator
Frequency
Address 0, Data 1
TA = 25°C
_
fOSC
2
MHz
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
%
2
ΔI(BL )
BL1-BL6 Current Matching
1.0
_
BL1-BL6 Charge Pump Mode
Transition Threshold
VBL_(TH)
150
mV
ENS Logic Control
VENS(L)
VENS(H)
IENS
tENS(LOW)
tENS(HI_MIN)
ENS Input Low Threshold
0.4
V
V
µA
µs
ENS Input High Threshold
ENS Input Leakage Current
ENS Serial Interface Low Time
ENS Serial Interface Minimum
1.4
-1.0
0.3
VENS = VIN = 5V
VIN ≥ 3.3V
1.0
75
,
50
ns
tENS(HI MIN) High Time
_
t
ENS(HI_MAX), ENS Serial Interface Maximum
VIN ≥ 3.3V
75
µs
µs
µs
tENS(HI MAX) High Time
_
tENS(OFF)
ENS Off Timeout
ENS Serial Interface Latch
Timeout
500
500
tENS(LAT)
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 correlation with statistical process controls.
2. Current matching is defined as the deviation of any sink current from the average of all active channels.
2856.2007.06.1.0
5
AAT2856
High Current Charge Pump with
Dual LDO for BacklightApplications
1
Electrical Characteristics
VIN = 3.6V; CIN = 4.7µF; COUT = 2.2µF; C1 = C2 = 1µF; RFSET = 280kΩ; TA = -40°C to +85°C, unless otherwise
noted. Typical values are TA = 25°C.
Symbol Description
Conditions
Min Typ Max Units
Linear Regulators
VFBA, VFBB Output Voltage Tolerance
IOUT = 1mA to 200mA
1.17 1.2
1.23
200
V
ENA = ENB = IN, ENS = AGND
ENA = IN, ENB = AGND or ENA =
AGND, ENB = IN, ENS = AGND
IIN
Ground Pin Current
µA
150
IOUTA(MAX)
IOUTB(MAX)
,
OUTA, OUTB Maximum Load
Current
200
150
50
mA
mV
dB
VOUTA(DO)
,
OUTA, OUTB Dropout Voltage
IOUT = 150mA
300
0.4
VOUTB(DO)
PSRRA,
PSRRB
OUTA, OUTB Power Supply
Rejection Ratio
ENA, ENB Voltage Low Threshold
ENA, ENB Voltage High Threshold
ENA, ENB Enable Delay
IOUT = 10mA, CREF = 10nF, 1kHz
VEN (L)
V
V
µs
_
VEN (H)
1.4
15
_
tEN (DLY)
REF = Open
_
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 correlation with statistical process controls.
6
2856.2007.06.1.0
AAT2856
High Current Charge Pump with
Dual LDO for BacklightApplications
Typical Characteristics
Backlight Efficiency vs. Input Voltage
Backlight Current Matching vs. Temperature
(20mA/Ch; Data 1)
100
21
20.5
20
90
20mA/ch
80
70
60
19.5
19
50
10.2mA/ch 1.6mA/ch
40
30
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)
2856.2007.06.1.0
7
AAT2856
High Current Charge Pump with
Dual LDO for BacklightApplications
Typical Characteristics
BENS, FENS High Threshold Voltage
vs. Input Voltage
BENS, FENS Low Threshold Voltage
vs. Input Voltage
1.4
1.3
1.4
1.3
-40°C
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
1.2
-40°C
1.1
1.0
0.9
0.8
0.7
25°C
85°C
85°C
25°C
0.6
0.5
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
VEN
(2V/div)
0.5
0.0
0V
0V
OUTA
OUTB
VOUT
(500mV/div)
-0.5
-1.0
0.1
1
10
100
1000
Time (50µs/div)
Load Current (mA)
8
2856.2007.06.1.0
AAT2856
High Current Charge Pump with
Dual LDO for BacklightApplications
Typical Characteristics
LDOs A and B Line Regulation
LDOs A and B Output Voltage
vs. Temperature
1.5
1.0
0.5
0
1
0.5
0
OUTA
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)
2856.2007.06.1.0
9
AAT2856
High Current Charge Pump with
Dual LDO for BacklightApplications
Functional Block Diagram
IN IN
C1+
OUTA
FBA
1X/1.5X/2X
C1-
Tri-mode
C2+
C2-
Charge Pump
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
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.
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 voltages as low as 1.2V.
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 con-
tinuously 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 pre-
vents the charge pump from oscillating between
charge pump modes.
LED Drivers
The LEDs are driven from an internal charge pump
that, depending on the battery voltage and LED for-
ward voltage, drives LEDs directly from the supply
voltage (1X or bypass mode) or steps up the sup-
ply 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 con-
verter solutions. Each individual LED is driven by a
The backlight LED current levels are dynamically
2
controllable by the AS Cwire single-wire interface.
The backlight section has multiple current level
10
2856.2007.06.1.0
AAT2856
High Current Charge Pump with
Dual LDO for BacklightApplications
2
scales and the maximum current level is fixed at
20mA or 30mA, depending on the scale chosen
through programming.
AS Cwire Serial Interface Addressing
ENS
Rising
If any one of the backlight or flash current sinks is
not used, connect that current sink to OUT. The
current controller monitors the sink voltage and, if it
is connected to OUT, then the controller deter-
mines that the current sink is not used or that the
LED is shorted. In either case, the controller turns
off the affected current sink.
Address Edges
Function
0
1
17
18
Backlight Current BL1-BL6
Main Backlight Current
BL1-BL5
2
3
12
19
20
29
Sub Backlight Current BL6
Low Current Backlight
Maximum Backlight Current
(Main and Sub)
2
AS Cwire Serial Interface
15
32
Backlight Independent
Control
The AAT2856 is dynamically programmable by the
2
2
AS Cwire single-wire interface. AS Cwire records
rising edges detected at the ENS pin to address
Sub-2
Sub-3
19
20
BL3-BL6 On/Off Control
BL1/BL2 On/Off Control
2
and load the data registers. AS Cwire latches data
2
or address after the ENS input has been held high
for time tLAT (500µs). Address or data is differenti-
ated by the number of ENS rising edges. Since the
data registers are 4 bits each, the differentiating
Table 1: AS Cwire Serial Interface Addressing.
Backlight Current Control (Address 0-3)
4
Use Addresses 0-3 to program all six backlight LED
channels. All six backlight channels are pro-
grammed 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.
number of pulses is 2 or 16, so that Address 0 is
identified by 17 rising edges, Address 1 by 18 ris-
ing 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 identifying 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 programmed and backlight chan-
nels BL1-BL6 will turn-on according to the number
of data edges applied.
Data
1
2
3
4
5
6
7
8
30mA Max (mA) 20mA Max (mA)
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
9
10
11
12
13
14
15
16
7.3
5.4
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 shut-
down, the data and address registers are reset to 0.
6.2
4.1
4.4
2.9
3.5
2.2
2.6
1.6
0
0
Table 2: Data for the Backlight Current Level
(Address 0-3).
2856.2007.06.1.0
11
AAT2856
High Current Charge Pump with
Dual LDO for BacklightApplications
Address
Data
THI
TLAT
TLO
TLAT
EN/SET
Address
1
2
17
18
1
2 . . .
n <= 16
0
1
0
0
n
Data Reg 1
Data Reg 2
2
Figure 1: AS Cwire Serial Interface Timing.
35.0
30.0
25.0
20.0
15.0
10.0
5.0
Main
Sub
Current
(µA)
Data
1
2
3
4
Current On Current On
No
No
No
No
No
No
0
0
0
30mA (Full Scale)
20mA (Full Scale)
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
0.0
500
950
1900
95
500
950
1900
95
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16
Data Code
9
Figure 2: Data Code for Address 0-3 vs.
Backlight Current Level.
10
11
12
13
14
15
16
The AAT2856 incorporates additional circuitry that
optimizes performance for exceptionally low back-
light current settings. A separate address is used to
activate this circuitry. To program the low current
settings with improved performance and efficiency,
write to Address 3. Unlike Addresses 0-2, which
have current level settings according to Table 2 and
Figure 2, Address 3 possesses a separate set of
current levels described by the Low Current
Backlight settings found in Table 3.
500
950
1900
Table 3: Low-Level Backlight Current,
Address 3, FS = 20mA range.
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.
12
2856.2007.06.1.0
AAT2856
High Current Charge Pump with
Dual LDO for BacklightApplications
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.
Data
1
2
3
4
5
6
7
8
BL6
BL5
BL4
BL3
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
Data
Maximum Current
1
2
20mA
30mA
Table 6: Address 12 Maximum Current
Settings.
9
10
11
12
13
14
15
16
Backlight Independent Channel Control
(Address 15)
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 8: Sub-Address 2: BL3-BL6
On/Off Control.
To enable independent channel control mode, write
Data 8 to Address 15. To exit individual mode con-
trol, the AAT2856 state machine can be reset by
strobing ENS low and holding ENS low longer than
Data
BL2
BL1
2
1
2
3
4
5
6
7
8
9
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
the A SCwire's tOFF latch time.
Data
Individual Backlight Control
8
On
Table 7: Address 15, Independent
Backlight Control.
With independent channel control mode enabled,
Addresses 2 and 3 are re-mapped according to
Tables 8 and 9. As indicated by the possible set-
tings listed in the tables, any combination of back-
lighting channels can be enabled and disabled.
10
11
12
13
14
15
16
Table 9: Sub-Address 3: BL1 and BL2
On/Off Control.
Because Addresses 2 and 3 are re-mapped when
independent channel control mode is enabled, the
functions originally assigned to Addresses 2 and 3
are no longer available.
2856.2007.06.1.0
13
AAT2856
High Current Charge Pump with
Dual LDO for BacklightApplications
It is also important to note that Address 0 is disabled
when independent channel control mode is enabled.
Additionally, Address 3 is disabled and the very low
current settings cannot be used in this mode. Other
addresses are unmodified by this mode so that the
30mA backlight scale can still be used.
Applications Information
LDO Output Voltage Programming
The output voltages for LDOA and LDOB are pro-
grammed by an external resistor divider network.
As shown below, the selection of R1 and R2 is a
straight forward matter.
The LDO enables are always independent of
2
AS Cwire programming.
R1 is chosen by considering the tradeoff between
the feedback network bias current and resistor
value. Higher resistor values allow stray capaci-
tance to become a larger factor in circuit perform-
ance whereas lower resistor values increase bias
current and decrease efficiency.
Low Dropout Regulators
The AAT2856 includes two independent LDO linear
regulators. 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 volt-
age dividers from the output (OUTA or OUTB) to
the feedback input (FBA or FBB). The regulator
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 cur-
rent allows the regulator to maintain output voltage
regulation.
OUT(A/B)
VOUT(A/B)
R2(A/B)
R1(A/B)
FB(A/B)
VREF(A/B) = 1.2V
Each LDO regulator can supply up to 200mA con-
tinuous current to the load. They include current
limiting and thermal overload protection to prevent
damage to the load or to the LDOs.
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, cal-
culate R2 according to the equation below. An exam-
ple calculation follows.
An R1 value of 120K is chosen, resulting in a small
feedback network bias current of 1.2V/120K = 10µA.
The desired output voltage is 1.8V. From this infor-
mation, R2 is calculated from the equation below.
R1(VOUT - 1.2V)
R2 =
1.2V
The result is R2 = 60K. Since 60K is not a standard
1%-value, 60.4K is selected. From this example
calculation, for VOUT = 1.8V, use R1 = 120K and R2
= 60.4K. Example output voltages and correspon-
ding resistor values are provided in Table 13.
14
2856.2007.06.1.0
AAT2856
High Current Charge Pump with
Dual LDO for BacklightApplications
mode when the input voltage drops too low in rela-
tion to the LED forward voltages.
R2 Standard 1% Values (R1 = 120K)
VOUT (V)
R2 (Ω)
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 effi-
ciency is given by:
2.8
2.5
2.0
1.8
1.5
160K
130K
79.6K
60.4K
30.1K
VF · ILED
VF
Table 13: Example Output Voltages and
Corresponding Resistor Values
η =
=
VIN · 1.5IIN 1.5 · VIN
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.
Similarly, when the input falls further, such that
1.5X mode can no longer sustain LED drive cur-
rent, the device will automatically switch to 2X
mode. In 2X mode, the output voltage can be
boosted to twice the input voltage. The doubling
conversion ratio introduces a corresponding dou-
bling of the input current. For ideal conversion, the
2X mode efficiency is given by:
Device Power Efficiency
The AAT2856 power conversion efficiency depends
on the charge pump mode. By definition, device effi-
ciency is expressed as the output power delivered to
the LEDs divided by the total input power consumed.
VF · ILED
VF
η =
=
VIN · 2IIN 2 · VIN
POUT
PIN
η =
LED Selection
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 pass-
ing the input supply directly to the output. By sim-
plifying the conditions such that the LEDs have uni-
form VF, the power conversion efficiency can be
approximated by:
The AAT2856 is designed to drive high-intensity
white LEDs. It is particularly suitable for LEDs with
an operating forward voltage in the range of 1.5V to
4.2V.
The charge pump can also drive other loads that
have similar characteristics to white LEDs. For var-
ious load types, the AAT2856 provides a high-cur-
rent, programmable ideal constant current source.
VF · ILED
VIN · IIN
VF
Capacitor Selection
η =
≈
VIN
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 per-
formance. Optimum performance will be obtained
when low equivalent series resistance (ESR)
ceramic capacitors are used. In general, low ESR
may be defined as less than 100mΩ.
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 AAT2856 further maintains optimized perform-
ance and efficiency by detecting when the input
voltage is not sufficient to sustain LED drive cur-
rent. The device automatically switches to 1.5X
Ceramic composition capacitors are highly recom-
mended over all other types of capacitors for use
with the AAT2856. Ceramic capacitors offer many
advantages over their tantalum and aluminum elec-
2856.2007.06.1.0
15
AAT2856
High Current Charge Pump with
Dual LDO for BacklightApplications
trolytic counterparts. 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 capacitors are
non-polarized, they are not prone to incorrect con-
nection damage.
Figure 6 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 fol-
lowing a couple of important PCB design guidelines.
Equivalent Series Resistance
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.
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 connections, size or area, material compo-
sition, and ambient temperature. Capacitor ESR is
typically measured in milliohms for ceramic capac-
itors and can range to more than several ohms for
tantalum or aluminum electrolytic capacitors.
The chip ground is internally connected to both the
paddle and to the AGND and PGND pins. It is good
practice to connect the GND pins to the exposed
paddle area with traces as shown in the example.
Ceramic Capacitor Materials
Ceramic capacitors less than 0.1µF are typically
made from NPO or C0G materials. NPO and C0G
materials generally have tight tolerance and are
very stable over temperature. Larger capacitor val-
ues are usually composed of X7R, X5R, Z5U, or
Y5V dielectric materials. Large ceramic capacitors
are often available in lower-cost dielectrics, but
capacitors greater than 10µF are not typically
required for AAT2856 applications.
The flying capacitors C1 and C2 should be con-
nected 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.
Capacitor area is another contributor to ESR.
Capacitors that are physically larger will have a
lower ESR when compared to an equivalent mate-
rial smaller capacitor. These larger devices can
improve circuit performance when compared to an
equal value capacitor in a smaller package size.
PCB Layout
To achieve adequate electrical and thermal per-
formance, 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.
Figure 6: Example PCB Layout.
16
2856.2007.06.1.0
AAT2856
High Current Charge Pump with
Dual LDO for BacklightApplications
Evaluation Board Layout
Figure 7: AAT2856 Evaluation Board
Figure 8: AAT2856 Evaluation Board
Layout Bottom Side.
Layout Top Side.
The Enables of both LDOs are connected with
jumpers J3 and J4. These terminals must be con-
nected to the external source to turn on/off the
LDOs.
Evaluation Board User Interface
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 combinations. The table below
indicates the function of each button or button
combination.
When applying external enable signals, considera-
tion must be given to the voltage levels. The exter-
nally applied voltages cannot exceed the supply volt-
age that is applied to the IN pins of the device (DC+).
To power-on the board, connect a power supply or
battery to the DC- and DC+ terminals. Make the
board's supply connection by positioning the J1
jumper to the ON position. A red LED indicates that
power is applied.
The LDO loads can be connected directly to the
evaluation board. For adequate performance, be
sure to connect the load between OUTA/OUTB and
DC- as opposed to some other GND in the system.
Button(s) Pushed
Description
SW1
[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.
SW2
SW3
[Push/Release once] Decrement the number of EN/SET edges, but the backlight cur-
rent is increased (brighter). If held down, auto-cycle through the settings.
[Push/Release once] Toggle between 20mA and 30mA maximum current.
1
Table 14: AAT2856 Evaluation Board User Interface .
1. The enable for LDOA and LDOB are manually set externally.
2856.2007.06.1.0
17
AAT2856
High Current Charge Pump with
Dual LDO for BacklightApplications
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
20
19
18
17
16
15
BL3
OUT
ENS
PGND
IN
BL2
BL1
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
R3
59k
V
OUT A/B(V) R2 (Ω), R1 = 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 9: AAT2856 Section Schematic
18
2856.2007.06.1.0
AAT2856
High Current Charge Pump with
Dual LDO for BacklightApplications
U3
VIN
AAT4296
1
2
3
4
8
7
IN
OUT3
OUT2
OUT1
OUT4
6
OUT5
5
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 10: MCU and I/O Expander Section Schematic
2856.2007.06.1.0
19
AAT2856
High Current Charge Pump with
Dual LDO for BacklightApplications
Evaluation Board Component Listing
Component
Part#
Description
Manufacturer
U1
AAT2856INJ-EE-T1
High Eff. 1X/1.5X/2X CP for White LED,
Dual LDO
AnalogicTech
U2
U3
PIC12F675
AAT4296IJS-1-T1
LW M673
GRM18x
GRM18x
GRM18x
GRM18x
TAJBx
Chip Resistor
Chip Resistor
Chip Resistor
Chip Resistor
Chip Resistor
Chip Resistor
PRPN401PAEN
CMD15-21SRC/TR8
PTS645TL50
8-bit CMOS, FLASH MCU; 8-pin PDIP
I/O Expander
Microchip
AnalogicTech
OSRAM
Murata
Murata
Murata
Murata
AVX
Vishay
Vishay
Vishay
Vishay
Vishay
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
C8, C11
C12
R8-R10
R7
R5, R6
R4
R2
R1, R3
J1-J4
LED7
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
Vishay
Sullins Electronics
Chicago Miniature Lamp
ITT Industries
SW1-SW3
Switch Tact, SPST, 5mm
20
2856.2007.06.1.0
AAT2856
High Current Charge Pump with
Dual LDO for BacklightApplications
Ordering Information
1
2
Package
Marking
Part Number (Tape and Reel)
TQFN44-28-0.4
XVXYY
AAT2856INJ-EE-T1
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/pbfree.
3
Package Information
TQFN44-28-0.4
2.400 REF
Detail "A"
C0.3
Pin 1 Dot
by Marking
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.
2856.2007.06.1.0
21
AAT2856
High Current Charge Pump with
Dual LDO for BacklightApplications
© 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 with-
out notice. Except as provided in AnalogicTech’s terms and conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied war-
ranty 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.
Advanced Analogic Technologies, Inc.
830 E. Arques Avenue, Sunnyvale, CA 94085
Phone (408) 737-4600
Fax (408) 737-4611
22
2856.2007.06.1.0
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