AAT3122
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
3122.2004.03.1.0
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 appli-
cations. With input voltages ranging from 2.7-5.5
Volts, 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.
AnalogicTechTM's Simple Serial ControlTM
(S
2
CwireTM) interface is used to enable, disable
and set the LED drive current with a 32 level loga-
rithmic scale LED brightness control. The AAT3122
has a thermal 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
external capacitors. A low shutdown current feature
disconnects the load from V
IN
and reduces quies-
cent current to less than 1A. The AAT3122 pro-
vides a single current source output that can be
used to drive up to 6 LEDs at 20mA each. The
AAT3122 is available in a 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 4 External components
Simple Serial ControlTM (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
-40 to +85C Temperature Range
Applications
White LED Backlighting
Programmable Current Source
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
3122.2004.03.1.0
Pin Descriptions
Pin Configuration
TSOPJW-12
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 + terminal. Connect a 1.0F Capacitor between C2+ and C2-
2
OUT
Charge pump output. Requires 1.0 F bypass capacitor to ground.
3
C1-
Flying Capacitor 1 - terminal
4
C1+
Flying Capacitor 1 + terminal. Connect a 1.0F 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 1uF bypass capacitor to ground.
11
GND
Ground
12
C2-
Flying Capacitor 2 - terminal
Absolute Maximum Ratings
1
Notes:
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.
Thermal Information
Note 3: Mounted on a FR4 board.
Note 4: Derate 6.25mW/C above 25C.
Symbol
Description
Value
Units
JA
Thermal Resistance
3
160
C/W
P
D
Maximum Power Dissipation (T
A
= 25C)
3, 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
3122.2004.03.1.0
3
AAT3122
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
4
3122.2004.03.1.0
Electrical Characteristics
1
V
IN
= 3.5V; C
IN
= C
OUT
= C
1
= C
2
= 1.0F; T
A
= -40 to 85C. Unless otherwise noted, typical values are T
A
= 25C
Note 1: The AAT3122 is guaranteed to meet performance specification over the -40 to +85C operating temperature range, and are
assured by design, characterization and correlation with statistical process controls.
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
Max. 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
= 3.6, I
OUT(Total)
= 120mA;
93
%
Measured from IN to OUT
EN/SET
V
EN(L)
Enable Threshold Low
V
IN
= 2.7 to 5.5V
0.5
V
V
EN(H)
Enable Threshold High
V
IN
= 2.7 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
AAT3122
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
3122.2004.03.1.0
5
Typical Characteristics
(unless otherwise noted: V
IN
= 3.6V, C
IN
= C
OUT
= C1 = C2 = 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. VIN (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
AAT3122
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
6
3122.2004.03.1.0
Typical Characteristics
(unless otherwise noted: V
IN
= 3.6V, C
IN
= C
OUT
= C1 = C2 = 1F, T
A
= 25C)
80mA Load Characteristics
1
s/div
20mV/div
V
IN
OUT
V
DIODE
Turn-Off
200
s/div
ENSET
(1V/div)
V
DIODE
(2V/div)
I
IN
(100mA/div)
Load Switch to Charge Pump (80mA)
50
s/div
V
IN
(20mV/div)
OUT
(1V/div)
V
DIODE
(1V/div)
I
IN
(200mV/div)
Charge Pump to Load Switch (80mA)
50
s/div
V
IN
(10mV/div)
OUT
(2V/div)
V
DIODE
(2V/div)
I
IN
(100mA/div)
Turn-On to Full Scale Load-Switch
50
s/div
ENSET
(1V/div)
OUT
(2V/div)
V
DIODE
(2V/div)
I
IN
(100mA/div)
Turn-On to Full Scale Charge-Pump
50
s/div
ENSET
(1V/div)
OUT
(2V/div)
V
DIODE
(1V/div)
I
IN
(200mA/div)
Functional Block Diagram
Voltage
Reference
Soft Start
1MHz
Oscillator
1.5X
Charge
Pump
S
2
Cwire
Interface
32x8 bit
ROM
Current
Mode
DAC
8
5
VIN
C1+
C1-
C2+
C2-
OUT
D
GND
EN/SET
AAT3122
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
3122.2004.03.1.0
7
Functional Description
The AAT3122 is a dual mode Load Switch (1X) and
high efficiency (1.5X) fractional charge pump device
intended for white LED back light applications. The
fractional charge pump consists of a low dropout lin-
ear voltage regulator followed by a 1.5X charge
pump. To maximize power conversion efficiency an
internal feedback control sensing circuit monitors
the voltage required on the constant current source
output. This control circuit then sets the load switch
and charge pump functions based upon the input
voltage level versus the output voltage level needed.
This function significantly enhances overall device
efficiency when the input voltage level is greater
than the voltage required at the constant current
source output. Switchover between the 1.5X
(charge pump) operating mode and the 1X (load
switch) mode occurs automatically (as a function of
input and output voltages) and does not require user
intervention to maintain maximum efficiency.
The AAT3122 requires only four external compo-
nents: two 1F ceramic capacitors for the charge
pump flying capacitors (C1 and C2), one 1F
ceramic capacitor for C
IN
, and one 0.33F to 1F
ceramic capacitor for C
OUT
. The LDO/1.5X charge
pump output is converted into a constant current
output capable of driving up to six individual LEDs
with a maximum of 20mA each. The current source
output magnitude is controlled by the EN/SET seri-
al data S
2
C interface. The interface records rising
edges of the EN/SET pin, and decodes them into
32 individual current level settings each 1dB apart.
This is summarized in figure and table 1. Code 32
is full scale, and Code 1 is full scale attenuated by
31dB. The modulo 32 interface wraps states back
to state 1 after the 32nd clock.
Applications Information
Current Level Settings
LED current level is set via the serial interface
according to a logarithmic scale where each code
is 1dB greater than the previous code. In this man-
ner, the LED brightness appears linear with each
increasing code. Table 1 depicts the relationship
between each rising edge of the EN/SET and the
output current in mA.
Table 1: Current Level Settings
EN/SET Serial Interface (S
2
CwireTM)
The current source output magnitude is controlled
by the EN/SET serial interface. The interface
records rising edges of the EN/SET pin, and
decodes them into 32 individual current level set-
tings each 1dB apart. Code 32 is full scale, and
Code 1 is full scale attenuated by 31dB. The mod-
ulo 32 interface wraps states back to state 1 after
the 32nd clock, so 1dB of attenuation is achieved
by clocking the EN/SET pin 31 times. The counter
can be clocked at speeds up to 1MHz, so interme-
diate states are not visible. The first rising edge of
EN/SET enables the IC and initially sets the output
LED current to 3.3mA, the lowest setting. Once the
final clock cycle is input for the desired brightness
level, the EN/SET pin is held high to maintain the
device output current at the programmed level. The
device is disabled 500s after the EN/SET pin tran-
sitions to a logic low state.
The EN/SET timing is designed to accommodate a
wide range of data rates. After the first rising edge
of EN/SET, the charge pump is enabled and reach-
es full capacity after the soft start time (TSS).
During the soft start time, multiple clock pulses may
be entered on the EN/SET pin to set the final output
current level with a single burst of clocks.
Alternatively, the EN/SET clock pulses may be
entered one at a time to gradually increase the LED
brightness over any desired time period. A constant
current is sourced as long as EN/SET remains in a
logic high state. The current source outputs are
switched off after EN/SET has remained in a low
state for at least the T
OFF
timeout period.
Code
I
OUT
(mA)
Code
I
OUT
(mA)
1
3.3
17
21.2
2
3.8
18
24.0
3
4.2
19
26.8
4
4.7
20
30.1
5
5.2
21
33.9
6
6.1
22
38.1
7
6.6
23
42.4
8
7.5
24
47.5
9
8.5
25
53.6
10
9.4
26
60.2
11
10.8
27
67.3
12
11.8
28
75.8
13
13.6
29
84.7
14
15.1
30
95.1
15
16.9
31
106.8
16
18.8
32
120.0
AAT3122
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
8
3122.2004.03.1.0
Normalized Current Level Settings
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
Code
Normalized Current to Full Scale
LED Selection
The AAT3122 is specifically intended for driving white
LED's. However, the device design will allow the
AAT3122 to drive most types of LED's with forward
voltage specifications ranging from 2.0-4.3V. LED
applications may include main and sub-LCD display
backlighting, camera photo-flash applications, color
(RGB) LED's, infrared (IR) diodes for remotes, and
other loads benefiting from a controlled output-cur-
rent generated from a varying input voltage.
Device Switching Noise Performance
The AAT3122 operates at a fixed frequency of
approximately 1MHz to control noise and limit har-
monics that can interfere with the RF operation of
cellular telephone handsets or other communica-
tion devices. Back-injected noise appearing on the
input pin of the Charge Pump is 20mV peak-to-
peak, typically ten times less than inductor-based
DC/DC boost converter white LED backlight solu-
tions. The AAT3122 soft-start feature prevents
noise transient effects associated with in-rush cur-
rents during the start up of the charge pump circuit.
Power Efficiency and Device
Evaluation
Due to the unique charge pump circuit architecture
and design of the AAT3122, it is very difficult to
measure efficiency in terms of a percent value
comparing input power over output power.
Since the AAT3122 output is purely a constant cur-
rent source, it is difficult to measure the output volt-
age to derive an overall output power measure-
ment. For any given application, white LED forward
voltage levels can differ, yet the output drive cur-
rent will be maintained as a constant.
This makes quantifying output power a difficult task
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 applica-
tion should be based on trade-offs of size, external
component count, reliability, operating range and
total energy usage...Not just "% efficiency".
Charge Pump Efficiency
The AAT3122 is a fractional charge pump. The effi-
ciency (
) can be simply defined as a linear voltage reg-
ulator with an effective output voltage that is equal to
one and a half times the input voltage. Efficiency (
) for
an ideal 1.5x charge pump can typically be expressed
as the output power divided by the input power.
=
P
OUT
P
IN
In addition, with an ideal 1.5x charge pump, the
output current may be expressed as 2/3 of the
input current. The expression to define the ideal
efficiency (
) can be rewritten as:
=
P
OUT
= (V
OUT
x I
OUT
)/(V
IN
x 1.5I
OUT
) =
V
OUT
P
IN
1.5V
IN
(%) = 100
V
OUT
1.5V
IN
For a charge pump with an output of 5 volts and a nom-
inal input of 3.5 volts, the theoretical efficiency is 95%.
Due to internal switching losses and IC quiescent cur-
rent consumption, the actual efficiency can be meas-
ured at 93%. These figures are in close agreement for
output load conditions from 3.0mA to 120mA. Efficiency
will decrease as load current drops below 0.05mA or
when the level of V
IN
approaches V
OUT
. Refer to the
Typical Characteristics section for measured plots of
efficiency versus input voltage and output load current
for the given charge pump output voltage options.
AAT3122
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
3122.2004.03.1.0
9
EN/SET Timing Diagram
EN/SET
Code
1
2
3
OFF
OFF
t
HI
t
LO
t
OFF
Capacitor Selection
Careful selection of the four external capacitors C
IN
,
C1, C2, C
OUT
is important because they will affect
turn on time, output ripple and transient performance.
Optimum performance will be obtained when low
ESR (<100m
) ceramic capacitors are used. In gen-
eral, low ESR may be defined as less than 100m
.
When choosing the four capacitors, a capacitor value
of 1F is a good starting point. If the LED current
sources are only programmed for light current levels,
then the capacitor size may be decreased.
Capacitor Characteristics
Ceramic composition capacitors are highly recom-
mended over all other types of capacitors for use
with the AAT3122 products. Ceramic capacitors
offer many advantages over their tantalum and alu-
minum electrolytic counterparts. A ceramic capaci-
tor 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
connection damage.
Equivalent Series Resistance (ESR): ESR is an
important characteristic to consider when selecting
a capacitor. ESR is a resistance internal to a
capacitor, which is caused by the leads, internal
connections, size or area, material composition
and ambient temperature. Capacitor ESR is typi-
cally measured in milliohms for ceramic capacitors
and can range to more than several ohms for tan-
talum or aluminum electrolytic capacitors.
Ceramic Capacitor Materials: Ceramic capacitors
less than 0.1F are typically made from NPO or COG
materials. NPO and COG materials typically have
tight tolerance and are stable over temperature. Large
capacitor values are typically composed of X7R, X5R,
Z5U or Y5V dielectric materials. Large ceramic capac-
itors, typically greater than 2.2F are often available in
low cost Y5V and Z5U dielectrics, but large capacitors
are not required in the AAT3122 application.
Capacitor area is another contributor to ESR.
Capacitors that are physically large will have a lower
ESR when compared to an equivalent material
smaller capacitor. These larger devices can improve
circuit transient response when compared to an
equal value capacitor in a smaller package size.
Thermal Protection
The AAT3122 has a thermal protection circuit that
will shut down the charge pump and current out-
puts if the die temperature rises above the thermal
limit due to short circuit conditions.
AAT3122
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
10
3122.2004.03.1.0
AAT3122
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
3122.2004.03.1.0
11
Additional Application Circuit
*In some applications, white LED forward voltages (V
F
) can vary significantly. Ballast resistors between the LED cathodes and ground are
recommended for balancing the forward voltage differences. The ballast resistor value may be approxiamted by the following equation:
R
B
=
(V
IN(MIN)
)1.5 - (V
F(MAX)
+ 250mV)
I
F(MAX)
V
F(MAX)
= Maximum expected LED forward voltage at the given maximum forward current level. Refer to the LED manufacturers'
datasheet for maximum V
F
specifications.
I
F(MAX)
= Maximum forward current used to drive an individual LED.
V
IN(MIN)
= Minimum input supply voltage for the application.
R
B
= Ballast resistor value in ohms.
C
IN
1
F
V
BATTERY
C
OUT
1
F
EN/SET
C1
1
F
C2
1
F
D2
D3
D4
D5
V
IN
V
OUT
C1+
C1-
C2+
C2-
D1
EN/SET
GND
AAT3122
D1
R
B
*
R
B
*
R
B
*
R
B
*
R
B
*
R
B
*
D6
AAT3122
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
12
3122.2004.03.1.0
Advanced Analogic Technologies, Inc.
830 E. Arques Avenue, Sunnyvale, CA 94085
Phone (408) 737-4600
Fax (408) 737-4611
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, and advise customers to obtain the latest
version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale
supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability.
AnalogicTech warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with AnalogicTech's standard warranty. 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.
Ordering Information
Note 1: XYY = assembly and date code.
Package Information
TSOPJW-12
All dimensions in millimeters.
0.20 + 0.10
- 0.05
0.055
0.045
0.45
0.15
7
NOM
4
4
3.00
0.10
2.40
0.10
2.85
0.20
0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC
0.15
0.05
0.9625
0.0375
1.00
+ 0.10
-
0.065
0.04 REF
0.010
2.75
0.25
Package
Marking
1
Part Number (Tape and Reel)
TSOPJW-12
JEXYY
AAT3122ITP-T1
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