AAT3157
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
ChargePump
TM
3157.2006.05.1.2
1
General Description
The AAT3157 is a low noise, constant frequency
charge pump DC/DC converter that uses a tri-
mode load switch (1X), fractional (1.5X), and dou-
bling (2X) conversion to maximize efficiency for
white LED applications. The AAT3157 is capable of
driving up to three channels of LEDs at 20mA per
channel from a 2.7V to 5.5V input. The current
sinks may be operated individually or in parallel for
driving higher current LEDs. A low external parts
count (two 1
F flying capacitors and two small 1F
capacitors at IN and OUTCP) make this part ideal-
ly suited for small, battery-powered applications.
AnalogicTech's S
2
Cwire
TM
(Simple Serial Control
TM
)
serial digital input is used to enable, disable, and set
current for each LED with 16 settings down to 50
A.
The low-current mode supply current can be as low
as 50
A to save power.
Each output of the AAT3157 is equipped with built-
in protection for output short-circuit and auto-dis-
able for load short-circuit conditions. Built-in soft-
start circuitry prevents excessive inrush current
during start-up. A low-current shutdown feature dis-
connects the load from the input and reduces qui-
escent current to less than 1
A.
The AAT3157 is available in a Pb-free, space-sav-
ing 2.85x3.0mm 12-pin TSOPJW package.
Features
V
IN
Range: 2.7V to 5.5V
Fully Programmable Current with Single Wire
-- 16 Current Levels
-- Four Low Current Settings Down to 50A
Low I
Q
(50A) for Low Current Mode
Tri-Mode 1X, 1.5X, and 2X Charge Pump for
Maximum Efficiency and V
F
Coverage
Drives up to Three Channels of LEDs
No Inductors, Low Noise Operation
1MHz Constant Switching Frequency
Small Application Circuit
Built-In Thermal Protection
Automatic Soft Start
I
Q
<1A in Shutdown
2.85x3.0mm TSOPJW-12 Package
Applications
Color (RGB) Lighting
Programmable Current Sinks
White LED Backlighting
White Photo Flash for Digital Still Cameras
Typical Application
2.7V to 5.5V
EN/SET
IN
EN/SET
C2+
C2-
C1+
C1-
OUTCP
D1
D2
D3
GND
AAT3157
D1
C1
1F
C2
1F
C
IN
1F
C
OUT
1F
D2
D3
Pin Descriptions
Pin Configuration
TSOPJW-12
(Top View)
1
2
3
4
5
6
12
11
10
9
8
7
D3
D2
D1
GND
IN
C2-
N/C
EN/SET
C1+
C1-
OUTCP
C2+
Pin #
Symbol
Function
1
D3
Current sink input #3.
2
D2
Current sink input #2.
3
D1
Current sink input #1.
4
GND
Ground.
5
IN
Input power supply. Requires 1F capacitor connected between this pin and
ground.
6
C2-
Flying capacitor 2 negative terminal.
7
C2+
Flying capacitor 2 positive terminal. Connect a 1F capacitor between C2+ and
C2-.
8
OUTCP
Charge pump output to drive load circuit. Requires 1F capacitor connected
between this pin and ground.
9
C1-
Flying capacitor 1 negative terminal.
10
C1+
Flying capacitor 1 positive terminal. Connect a 1F capacitor between C1+ and
C1-.
11
EN/SET
S
2
Cwire serial interface control pin.
12
N/C
No connection.
AAT3157
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
2
3157.2006.05.1.2
Absolute Maximum Ratings
1
Thermal Information
3
Symbol
Description
Value
Units
P
D
Maximum Power Dissipation
4
0.625
W
JA
Maximum Thermal Resistance
160
C/W
Symbol
Description
Value
Units
V
IN
Input Voltage to GND
-0.3 to 6
V
V
EN/SET
EN/SET Voltage to GND
-0.3 to V
IN
+ 0.3
V
I
OUT
2
Maximum DC Output Current
150
mA
T
J
Operating Junction Temperature Range
-40 to 150
C
T
LEAD
Maximum Soldering Temperature (at leads, 10 sec)
300
C
AAT3157
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
3157.2006.05.1.2
3
1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at condi-
tions 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. Mounted on an FR4 board.
4. Derate 6.25mW/C above 25C.
Electrical Characteristics
1
C
IN
= C
OUT
= C
1
= C
2
= 1.0F; T
A
= -40C to +85C, unless otherwise noted.
Typical values are T
A
= 25C, V
IN
= 3.6V.
Symbol
Description
Conditions
Min
Typ
Max Units
Input Power Supply
V
IN
Operation Range
2.7
5.5
V
1X Mode, 3.0
V
IN
5.5, Active,
0.3
1
No Load Current
1.5X Mode, 3.0
V
IN
5.5, Active,
1
3
mA
I
CC
Operating Current
No Load Current
2X Mode, 3.0
V
IN
5.5, Active,
1
No Load Current
50A Setting, 1X Mode
50
A
I
SHDN
Shutdown Current
V
EN/SET
= 0V
1
A
I
DX
I
SINK
Average Current Accuracy
I
SET
= 20mA, T
A
= 25C
18
20
22
mA
I
(D-Match)
Current Matching
2
V
F
:D1:D3 = 3.6V
0.5
1
%
V
TH
1X to 1.5X or 1.5X to 2X Transition
150
mV
Threshold at Any I
SINK
Pin
Charge Pump Section
T
SS
Soft-Start Time
100
s
F
CLK
Clock Frequency
1000
kHz
EN/SET
V
EN(L)
Enable Threshold Low
V
IN
= 2.7V
0.4
V
V
EN(H)
Enable Threshold High
V
IN
= 5.5V
1.4
V
T
EN/SET LO
EN/SET Low Time
0.3
75
s
T
EN/SET_HI_MIN
Minimum EN/SET High Time
50
ns
T
EN/SET_HI_MAX
Maximum EN/SET High Time
75
s
T
OFF
EN/SET Off Timeout
500
s
T
LAT
EN/SET Latch Timeout
500
s
I
EN/SET
EN/SET Input Leakage
-1
1
A
AAT3157
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
4
3157.2006.05.1.2
1. The AAT3157 is guaranteed to meet performance specifications over the -40C to +85C 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.
Typical Characteristics
C
IN
= C
OUT
= C
1
= C
2
= 1.0F; T
A
= 25C, V
IN
= 3.6V, unless otherwise noted.
Diode Current vs. Temperature
(20mA/ch)
Temperature (
C)
Diode Current (mA)
18.0
18.5
19.0
19.5
20.0
20.5
21.0
21.5
22.0
-40
-25
-10
5
20
35
50
65
80
I
D3
I
D2
I
D1
Turn-Off to 1.5X Mode
(V
IN
= 3.5V; 20mA/ch Load)
Time (100s/div)
EN/SET
(2V/div)
V
LED
(1V/div)
I
IN
(100mA/div)
Turn-On to 2X Mode
(V
IN
= 2.8V; 20mA/ch Load)
Time (100s/div)
EN/SET
(2V/div)
V
OUT
(2V/div)
I
IN
(200mA/div)
V
SINK
(2V/div)
Turn-On to 1.5X Mode
(V
IN
= 3.5V; 20mA/ch Load)
Time (100s/div)
EN/SET
(2V/div)
V
OUT
(2V/div)
I
IN
(100mA/div)
V
SINK
(2V/div)
Turn-On to 1X Mode
(V
IN
= 4.2V; 20mA/ch Load)
Time (100
s/div)
EN/SET
(2V/div)
V
OUT
(2V/div)
I
IN
(100mA/div)
V
SINK
(2V/div)
Efficiency vs. Supply Voltage
Supply Voltage (V)
Efficiency (%)
30
40
50
60
70
80
90
100
2.7
2.9
3.1
3.3
3.5
3.7
3.9
4.1
4.3
5mA/ch
V
F
= 2.7V
20mA/ch
V
F
= 3.4V
10mA/ch
V
F
= 3.1V
AAT3157
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
3157.2006.05.1.2
5
3157.2006.05.1.2
5
PDF 
ZIP