AAT3122
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
3122.2005.11.1.3
1
ChargePump
TM
General Description
The AAT3122 is a low noise, constant frequency
charge pump DC/DC converter that uses a dual
mode load switch (1X) and fractional (1.5X) con-
version to increase efficiency in white LED applica-
tions. With input voltages ranging from 2.7V to
5.5V, the device can produce an output current of
up to 120mA. A low external parts count (two 1F
flying capacitors and two small bypass capacitors
at V
IN
and OUT) makes the AAT3122 ideally suited
for small battery-powered applications.
AnalogicTech's Simple Serial ControlTM (S
2
CwireTM)
interface is used to enable, disable, and set the
LED drive current with a 32-level logarithmic scale
LED brightness control. The AAT3122 has a ther-
mal management system to protect the device in
the event of a short-circuit condition on any of the
output pins. Built-in soft-start circuitry prevents
excessive inrush current during start-up. High
switching frequency enables the use of small exter-
nal capacitors. A low shutdown current feature dis-
connects the load from V
IN
and reduces quiescent
current to less than 1A. The AAT3122 provides a
single current source output that can be used to
drive up to six LEDs at 20mA each. The AAT3122
is available in a Pb-free TSOPJW-12 package.
Features
V
IN
Range: 2.7V to 5.5V
<1A of Shutdown Current
1 MHz Switching Frequency
Dual Mode 1X and 1.5X Charge Pump for
Maximum Efficiency
Only Four External Components
Simple Serial Control (S
2
Cwire) Interface
Low Noise Constant Frequency Operation
33% Less Input Current Than Doubler Charge
Pumps
Small Application Circuit
Regulated Output Current
Automatic Soft Start
No Inductors
TSOPJW-12 Package
-40C to +85C Temperature Range
Applications
Programmable Current Source
White LED Backlighting
Typical Application
C
IN
1
F
V
BATTERY
C
OUT
1
F
EN/SET
C1
1
F
C2
1
F
D1
V
IN
V
OUT
C1+
C1-
C2+
C2-
D
EN/SET
GND
AAT3122
D2
D3
D4
D5
D6
AAT3122
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
2
3122.2005.11.1.3
Pin Descriptions
Pin Configuration
TSOPJW-12
(Top View)
1
2
3
4
5
6
12
11
10
9
8
7
C2+
OUT
C1-
C1+
D
D
C2-
GND
IN
EN/SET
D
D
Pin #
Symbol
Function
1
C2+
Flying capacitor 2 positive terminal. Connect a 1F capacitor between C2+ and C2-.
2
OUT
Charge pump output. Requires 1F bypass capacitor to ground.
3
C1-
Flying capacitor 1 negative terminal.
4
C1+
Flying capacitor 1 positive terminal. Connect a 1F capacitor between C1+ and C1-.
5, 6, 7, 8
D
Output current source with drive capability of up to 120mA.
9
EN/SET
Input control pin. Serial data interface that controls the level of output current. See
Application Information for more details.
10
IN
Input power supply. Requires 1F bypass capacitor to ground.
11
GND
Ground.
12
C2-
Flying capacitor 2 negative terminal.
Absolute Maximum Ratings
1
Thermal Information
3
Symbol
Description
Value
Units
JA
Thermal Resistance
160
C/W
P
D
Maximum Power Dissipation (T
A
= 25C)
4
625
mW
Symbol
Description
Value
Units
V
IN
Input Voltage
-0.3 to 6.0
V
V
OUT
Charge Pump Output
-0.3 to 6.0
V
V
EN/SET
EN/SET to GND Voltage
-0.3 to 6.0
V
V
EN/SET(MAX)
Maximum EN/SET to Input Voltage
0.3
V
I
OUT
2
Maximum DC Output Current
150
mA
T
J
Operating Junction Temperature Range
-40 to 150
C
AAT3122
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
3122.2005.11.1.3
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.
AAT3122
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
4
3122.2005.11.1.3
Electrical Characteristics
1
V
IN
= 3.5V; C
IN
= C
OUT
= C
1
= C
2
= 1.0F; T
A
= -40C to +85C. Unless otherwise noted, typical values are
T
A
= 25C.
Symbol
Description
Conditions
Min
Typ
Max
Units
Input Power Supply
V
IN
Operation Range
2.7
5.5
V
I
cc
Operating Current
3.0
V
IN
5.5, Active,
1.8
3.5
mA
No Load Current
I
SHDN
Shutdown Current
EN = 0
1.0
A
I
D
Maximum Output Current
V
IN
= 3.5V; Code = 32
108
120
132
mA
Charge Pump
T
SS
Soft-Start Time
200
s
F
CLK
Clock Frequency
1000
kHz
CP
Charge Pump Efficiency
V
IN
= 3.6V, I
OUT(Total)
= 120mA;
93
%
Measured from IN to OUT
EN/SET
V
EN(L)
Enable Threshold Low
V
IN
= 2.7V to 5.5V
0.5
V
V
EN(H)
Enable Threshold High
V
IN
= 2.7V to 5.5V
1.4
V
T
LO
EN/SET Low Time
0.3
75
s
T
HI
Minimum EN/SET High Time
50
ns
T
OFF
EN/SET Off Timeout
500
s
Input Current
EN/SET Input Leakage
-1.0
1.0
A
1. The AAT3122 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.
AAT3122
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
3122.2005.11.1.3
5
Typical Characteristics
Unless otherwise noted, V
IN
= 3.6V, C
IN
= C
OUT
= C
1
= C
2
= 1F, T
A
= 25C.
V
IH
and V
IL
vs. V
IN
0.600
0.625
0.650
0.675
0.700
0.725
0.750
0.775
0.800
0.825
0.850
2.5
3.0
3.5
4.0
4.5
5.0
5.5
V
IN
(V)
V
IH
V
IL
Quiescent Current vs. V
IN
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.50
3.00
3.50
4.00
4.50
5.00
5.50
V
IN
(V)
Quiescent Current (mA)
V
DIODE
= 3.3V
V
DIODE
= 3.4V
V
DIODE
= 3.5V
V
DIODE
= 3.6V
I
DIODE
vs. V
IN
40
45
50
55
60
65
70
75
80
85
90
2.7 2.9
3.1 3.3
3.5
3.7
3.9
4.1 4.3
4.5
4.7 4.9
5.1
V
IN
(V)
I
DIODE
(mA)
V
DIODE
= 3.3V
V
DIODE
= 3.4V V
DIODE
= 3.5V
V
DIODE
= 3.6V
Efficiency vs. V
IN
(I
D
= 80mA)
50
55
60
65
70
75
80
85
90
95
100
2.7 2.9
3.1 3.3
3.5 3.7 3.9
4.1 4.3
4.5
4.7 4.9
5.1
V
IN
(V)
Efficiency (%)
V
DIODE
= 3.3V
V
DIODE
= 3.4V
V
DIODE
= 3.5V
V
DIODE
= 3.6V
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