Analogic AAT3131ITP-T1 High efficiency 1x/1.5x fractional charge pump for white led application Datasheet

AAT3131
High Efficiency 1X/1.5X Fractional
Charge Pump for White LED Applications
General Description
Features
The AAT3131 is a low noise, constant frequency
charge pump DC/DC converter that uses a dual
mode load switch (1X) and fractional (1.5X) conversion to maximize efficiency for white LED applications. The device can be used to produce current levels up to 20mA in three of its outputs and
30mA in one of its outputs to drive LEDs from a
2.7V to 5.5V input. Outputs may be operated individually or paralleled for driving higher-current
LEDs. A low external parts count (two 1µF flying
capacitors and two small 1µF capacitors at VIN and
OUT) makes the AAT3131 ideally suited for small
battery-powered applications.
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
AnalogicTech's Simple Serial Control™ (S2Cwire™)
interface is used to enable, disable, and set the LED
drive current in two groups: the three 20mA outputs
and the single 30mA output with multiple level logarithmic scales. The AAT3131 has a thermal management system to protect the device in the event of
a short-circuit condition at the output pin. Built-in
soft-start circuitry prevents excessive inrush current
during start-up. A high charge pump switching frequency enables the use of very small external
capacitors. A low-current shutdown feature disconnects the load from VIN and reduces quiescent current to less than 1µA. The AAT3131 is available in
a Pb-free 12-pin TSOPJW12 package and is rated
over the -40°C to +85°C temperature range.
ChargePump™
VIN Range: 2.7V to 5.5V
<1.0µA of Shutdown Current
1MHz Switching Frequency
White LED Backlighting
Fully Independent Display Lighting
Dual Mode 1X and 1.5X Charge Pump for
Maximum Efficiency
Drives Low-VF and High-VF Type LEDs
Up to Three 20mA Outputs
Single 30mA Output
Multi-Position Logarithmic Scale with Digital
Control
Low Noise Constant Frequency Operation
Regulated Output Current
Automatic Soft Start
No Inductors
Temperature Range: -40°C to +85°C
12-Pin TSOPJW Package
Applications
•
•
•
•
Color (RGB) Lighting
Programmable Current Source
White LED Backlighting
White Photo Flash for Digital Still Cameras
Typical Application
VIN
C1+
C1
1µF
VOUT
VBATTERY
CIN
1µF
COUT
1µF
C1C2+
AAT3131
C2
1µF
C2D1
D2
D3
D4
EN/SET
EN/SET
D5
D4
D3
D2
D1
GND
3131.2005.12.1.2
1
AAT3131
High Efficiency 1X/1.5X Fractional
Charge Pump for White LED Applications
Pin Descriptions
Pin #
Symbol
Function
1
C2+
Flying capacitor 2 positive terminal. Connect a 1µF capacitor between C2+
and C2-.
2
OUT
Charge pump output. Requires 1µF capacitor connected between this pin and
ground.
3
C1-
Flying capacitor 1 negative terminal.
4
C1+
Flying capacitor 1 positive terminal. Connect a 1µF capacitor between C1+
and C1-.
5
D3
Current source output #3.
6
D2
Current source output #2.
7
D4
Current source output #4.
8
D1
Current source output #1.
9
EN/SET
10
IN
11
GND
12
C2-
Control pin.
Input power supply. Requires 1µF capacitor connected between this pin and
ground.
Ground.
Flying capacitor 2 negative terminal.
Pin Configuration
TSOPJW-12
(Top view)
C2+
OUT
C1C1+
D3
D2
2
1
12
2
11
3
10
4
9
5
8
6
7
C2GND
IN
EN/SET
D1
D4
3131.2005.12.1.2
AAT3131
High Efficiency 1X/1.5X Fractional
Charge Pump for White LED Applications
Absolute Maximum Ratings1
Symbol
VIN
VOUT
FB, VEN/SET
VEN/SET(MAX)
IOUT2
TJ
TLEAD
Description
Input Voltage
Charge Pump Output
FB or EN/SET to GND Voltage
Maximum EN/SET to Input Voltage
Maximum DC Output Current
Operating Junction Temperature Range
Maximum Soldering Temperature (at leads, 10 sec)
Value
Units
-0.3 to 6
-0.3 to 6
-0.3 to 6
VIN - 0.3
150
-40 to 150
300
V
V
V
V
mA
°C
°C
Value
Units
160
625
°C/W
mW
Thermal Information3
Symbol
θJA
PD
Description
Thermal Resistance
Maximum Power Dissipation4 (TA = 25°C)
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. Based on long-term current density limitation.
3. Mounted on an FR4 board.
4. Derate 6.25mW/°C above 25°C.
3131.2005.12.1.2
3
AAT3131
High Efficiency 1X/1.5X Fractional
Charge Pump for White LED Applications
Electrical Characteristics1
VIN = 3.5V, CIN = COUT = C1 = C2 = 1.0µF; TA = -40 to +85°C, unless otherwise noted. Typical values are TA = 25°C.
Symbol
Description
Conditions
Input Power Supply
VIN
Operation Range
ICC
ISHDN
IDX
IDX
I(D-Match)
ηCP
Charge Pump
TSS
FCLK
EN/SET
VEN(L)
VEN(H)
TEN/SET LO
TEN/SET HI
TOFF
Input Current
Operating Current
Shutdown Current
Maximum Output Current
D1 to D3
Maximum Output Current D4
Current Matching Between
Any Two Outputs
Charge Pump Section Efficiency
Min
2.7
3.0 ≤ VIN ≤ 5.5, Active,
No Load Current
EN = 0
1.8
Max
Units
5.5
V
3.5
mA
1.0
3.0 ≤ VIN ≤ 5.5
18
20
22
µA
A
m
3.0 ≤ VIN ≤ 5.5
27
30
33
mA
VD1:D3 = 3.6, VIN = 3.3V
0.5
%
VIN = 3.5V, IOUT(TOTAL) = 90mA,
Measured from IN to OUT
93
%
200
1000
µs
kHz
Section
Soft-Start Time
Clock Frequency
Enable Threshold Low
Enable Threshold High
EN/SET Low Time
Minimum EN/SET High Time
EN/SET Off Timeout
EN/SET Input Leakage
Typ
0.5
VEN/SET < 0.5
VEN/SET > 1.4
VEN/SET < 0.5
1.4
0.3
75
50
-1
500
1
V
V
µs
ns
µs
µA
1. The AAT3131 is guaranteed to meet performance specifications over the -40 to +85°C operating temperature range and is assured
by design, characterization, and correlation with statistical process controls.
4
3131.2005.12.1.2
AAT3131
High Efficiency 1X/1.5X Fractional
Charge Pump for White LED Applications
Typical Characteristics
Efficiency vs. Input Voltage
IDIODE vs. Input Voltage
(4x20mA)
(4x20mA)
100
90
95
85
90
VDIODE = 3.3V
80
85
VDIODE = 3.4V
75
IDIODE (mA)
Efficiency (%)
Unless otherwise noted, VIN = 3.5V, CIN = COUT = C1 = C2 = 1µF, TA = 25°C.
80
75
VDIODE = 3.5V
70
65
VDIODE = 3.6V
VDIODE = 3.3V
VDIODE = 3.4V
70
65
60
55
50
60
55
45
50
40
2.7
2.9
3.1
3.3
3.5
3.7
3.9
4.1 4.3
4.5
4.7 4.9
2.7
5.1
2.9
3.1
3.3
3.5
3.9
4.1
4.3
4.5
4.7
4.9
5.1
VIH and VIL vs. VIN
Quiescent Current vs. Input Voltage
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
2.50
3.7
Input Voltage (V)
Input Voltage (V)
Quiescent Current (mA)
VDIODE = 3.5V
VDIODE = 3.6V
0.850
0.825
0.800
0.775
VIH
0.750
VDIODE = 3.3V
0.725
VDIODE = 3.4V
0.700
VDIODE = 3.5V
0.675
VDIODE = 3.6V
0.650
VIL
0.625
0.600
3.00
3.50
4.00
4.50
Input Voltage (V)
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5.00
5.50
2.5
3.0
3.5
4.0
4.5
5.0
5.5
VIN (V)
5
AAT3131
High Efficiency 1X/1.5X Fractional
Charge Pump for White LED Applications
Typical Characteristics
Unless otherwise noted, VIN = 3.5V, CIN = COUT = C1 = C2 = 1µF, TA = 25°C.
Turn-On to Full-Scale Charge Pump
Turn-On to Full-Scale Load Switch
ENSET
(1V/div)
ENSET
(1V/div)
OUT
(2V/div)
OUT
(2V/div)
VDIODE
(1V/div)
VDIODE
(2V/div)
IIN
(200mA/div)
IIN
(100mA/div)
Time (50µs/div)
Time (50µs/div)
Charge Pump to Load Switch
Load Switch to Charge Pump
(80mA)
(80mA)
VIN
(10mV/div)
VIN
(20mV/div)
OUT
(2V/div)
OUT
(1V/div)
VDIODE
(2V/div)
VDIODE
(1V/div)
IIN
(100mA/div)
IIN
(200mV/div)
Time (50µs/div)
Time (50µs/div)
Turn-Off
80mA Load Characteristics
VIN
20mV/div
ENSET
(1V/div)
VDIODE
(2V/div)
OUT
IIN
(100mA/div)
VDIODE
Time (200µs/div)
6
Time (1µs/div)
3131.2005.12.1.2
AAT3131
High Efficiency 1X/1.5X Fractional
Charge Pump for White LED Applications
Functional Block Diagram
VIN
Soft-Start
Control
1X/1.5X
Charge
Pump
1MHz
Oscillator
Voltage
Reference
C1+
C1C2+
C2OUT
Current
Reference
Quad
Output
DAC
D1
D2
D3
32x16 bit
ROM
EN/SET
S2Cwire
Interface
Single
Output
DAC
32x16 bit
ROM
D4
GND
Functional Description
The AAT3131 is a dual mode load switch (1X) and
high efficiency (1.5X) fractional charge pump
device intended for white LED backlight applications. The fractional charge pump consists of a low
dropout linear voltage regulator followed by a 1.5X
charge pump with multiple current-source outputs.
To maximize power conversion efficiency, an internal feedback control sensing circuit monitors the
voltage required on the constant current source
outputs. 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 outputs. The 1X load switch/1.5X
charge pump mode decision is based on the voltage levels sensed on either the D1 output or the
D4 output, whichever is greater. Switchover
3131.2005.12.1.2
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 AAT3131 requires only four external components: two 1µF ceramic capacitors for the charge
pump flying capacitors (C1 and C2), one 1µF
ceramic input capacitor (CIN), and one 0.33µF to
1µF ceramic output capacitor (COUT). The
LDO/1.5X charge pump output is converted into
three (D1 to D3) constant current outputs to drive
three individual LEDs with a maximum current of
20mA each, and one (D4) constant current output
with a maximum current of 30mA. The current
source output magnitude is controlled by the
EN/SET serial data interface. The interface records
rising edges of the EN/SET pin and decodes them
into 32 addresses corresponding to individual current level settings. The 32 addresses are divided
7
AAT3131
High Efficiency 1X/1.5X Fractional
Charge Pump for White LED Applications
such that outputs D1 to D3 can be controlled independently of output D4. For Addresses 1 to 8, 9 to
16, 17 to 24, and 25 to 32, outputs D1 to D3 start
at 0mA and increase from 0.5mA to 20mA in three
8dB steps and three 2.5dB steps. Output D4
remains constant over these address ranges,
which provides orthogonal control of the two channels. For Addresses 1 to 8, D4 is set to 0mA; for
Addresses 9 to 16, D4 is set to 1mA; for Addresses
17 to 24, D4 is set to 15mA; and for Addresses 25
to 32, D4 is set to 30mA. This is summarized in
Table1 and Figure 1.
Applications Information
Constant Current Output Level Settings
The constant current source output amplitude for
outputs D1 to D3 and D4 are set via the serial interface according to a logarithmic scale. Using a logarithmic scale, LED brightness appears linear with
each increasing code count. Because the outputs
D1 to D4 are true independent constant current
sources, the voltage observed on any single given
output will be determined by the actual forward
voltage (VF) for the LED being driven.
The modulo 32 interface wraps states back to State 1
after the 32nd clock. With each EN/SET pulse, the
output current changes to the next setting in the
address decoding. To change settings to the previous
address decoding, 31 EN/SET clock pulses are
required. The counter can be clocked at speeds up to
1MHz, so that intermediate states are not visible. The
first rising edge of EN/SET enables the IC and initially sets the output LED currents to 0mA. Additional
clocks are required to set the desired current level.
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 500µs after the EN/SET
pin transitions to a logic low state.
Since the output current of the AAT3131 is programmable through its S2Cwire interface, no PWM (pulse
width modulation) or additional control circuitry are
needed to control LED brightness. This feature
greatly reduces the burden on a microcontroller or
system IC to manage LED or display brightness,
allowing the user to "set it and forget it."
Furthermore, with its high-speed serial interface
(1MHz data rate), the output current of the AAT3131
can be changed successively to brighten or dim
LEDs in smooth transitions (e.g., to fade out) or in
abrupt steps, giving the user complete programmability and real-time control of LED brightness.
30
25
Current (mA)
20
15
10
5
0
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
Address Code
Figure 1: Output Level Current Settings.
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3131.2005.12.1.2
AAT3131
High Efficiency 1X/1.5X Fractional
Charge Pump for White LED Applications
Address
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
Current Level Settings (mA)
D1-3
D4
0.0
0.5
1.3
3.3
8.3
11.1
15.0
20.0
0.0
0.5
1.3
3.3
8.3
11.1
15.0
20.0
0.0
0.5
1.3
3.3
8.3
11.1
15.0
20.0
0.0
0.5
1.3
3.3
8.3
11.1
15.0
20.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
15.0
15.0
15.0
15.0
15.0
15.0
15.0
15.0
30.0
30.0
30.0
30.0
30.0
30.0
30.0
30.0
EN/SET Serial Interface
The current source output magnitude is controlled
by the EN/SET serial data interface. The interface
records rising edges of the EN/SET pin and decodes
them into 32 individual current level settings. The
modulo 32 interface wraps states back to State 1
after the 32nd clock, so that the previous state is
achieved by clocking the EN/SET pin 31 times. The
counter can be clocked at speeds up to 1MHz, so
that intermediate states are not visible. The first rising edge of EN/SET enables the IC and initially sets
the output LED current to 0dB. 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 500µs after the EN/SET pin transitions 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 reaches 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 TOFF timeout period.
Table 1: Constant Current Source Output
Programming Levels.
3131.2005.12.1.2
9
AAT3131
High Efficiency 1X/1.5X Fractional
Charge Pump for White LED Applications
EN/SET Timing Diagram
tHI
tOFF
tLO
EN/SET
Code
OFF
1
LED Selection
The AAT3131 is specifically intended for driving
white LEDs. However, the device design will allow
the AAT3131 to drive most types of LEDs with forward voltage specifications ranging from 2.0V to
4.3V. LED applications may include main and subLCD display backlighting, camera photo-flash applications, color (RGB) LEDs, infrared (IR) diodes for
remotes, and other loads benefiting from a controlled output current generated from a varying input
voltage. Since the D1 to D4 output current sources
are matched with negligible voltage dependence,
the LED brightness will be matched regardless of
the specific LED forward voltage (VF) levels.
In some instances (e.g., in high luminous output
applications such as photo flash), it may be necessary to drive high-VF type LEDs. The low dropout
current sources in the AAT3131 makes it capable
of driving LEDs with forward voltages as high as
4.3V at full current from an input supply as low as
3.0V. Outputs can be paralleled to drive high-current LEDs without complication.
2
3
OFF
Power Efficiency and Device
Evaluation
The charge pump efficiency discussion in the following sections only accounts for efficiency of the
charge pump section itself. Due to the unique circuit
architecture and design of the AAT3131, it is very
difficult to measure efficiency in terms of a percent
value comparing input power over output power.
Since the AAT3131 outputs are pure constant current sources and typically drive individual loads, it
is difficult to measure the output voltage for a given
output (D1 to D4) to derive an overall output power
measurement. For any given application, white
LED forward voltage levels can differ, yet the output drive current will be maintained as a constant.
Device Switching Noise Performance
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 application should be based on trade-offs of size, external
component count, reliability, operating range, and
total energy usage...not just % efficiency.
The AAT3131 operates at a fixed frequency of
approximately 1MHz to control noise and limit harmonics that can interfere with the RF operation of
cellular telephone handsets or other communication devices. Back-injected noise appearing on the
input pin of the charge pump is 20mV peak-topeak, typically ten times less than inductor-based
DC/DC boost converter white LED backlight solutions. The AAT3131 soft-start feature prevents
noise transient effects associated with inrush currents during start-up of the charge pump circuit.
The AAT3131 efficiency may be quantified under
very specific conditions and is dependent upon the
input voltage versus the output voltage seen
across the loads applied to outputs D1 through D4
for a given constant current setting. Depending
upon the case of VIN being greater than the specific voltage seen across the load on D1 (or D4), the
device will operate in load switch mode. If VIN is
less than the voltage required on the constant current source, the device will operate in 1.5X charge
pump mode. Each of these two modes will yield
10
3131.2005.12.1.2
AAT3131
High Efficiency 1X/1.5X Fractional
Charge Pump for White LED Applications
different efficiency values. Refer to the following
two sections for explanations for each operational
mode.
input current. The expression to define the ideal
efficiency (η) can be rewritten as:
η=
Load Switch Mode Efficiency
The AAT3131 load switch mode is operational at all
times and functions alone to enhance device power
conversion efficiency when VIN is greater than voltage across the load connected to the constant current source outputs. When in load switch mode,
the voltage conversion efficiency is defined as output power divided by input power:
η=
POUT
PIN
The expression to define the ideal efficiency (η)
can be rewritten as:
η=
POUT VOUT × IOUT VOUT
=
=
PIN
VIN × IOUT
VIN
POUT
VOUT × IOUT
VOUT
=
=
PIN
VIN × 1.5IOUT 1.5VIN
-orη(%) = 100
⎛ VOUT ⎞
⎝ 1.5VIN⎠
For a charge pump with an output of 5V and a nominal input of 3.5V, the theoretical efficiency is 95%.
Due to internal switching losses and IC quiescent
current consumption, the actual efficiency can be
measured at 93%. These figures are in close agreement for output load conditions from 1mA to 100mA.
Efficiency will decrease as load current drops below
0.05mA, or when level of VIN approaches VOUT.
Refer to the Typical Characteristics section of this
datasheet for measured plots of efficiency versus
input voltage and output load current for the given
charge pump output voltage options.
-or-
Capacitor Selection
η(%) = 100
⎛ VOUT ⎞
⎝ VIN ⎠
Charge Pump Section Efficiency
The AAT3131 contains a fractional charge pump
which will boost the input supply voltage in the
event that VIN is less than the voltage required on
the constant current source outputs. The efficiency (η) can be simply defined as a linear voltage
regulator with an effective output voltage that is
equal to one and one half times the input voltage.
Efficiency (η) for an ideal 1.5X charge pump can
typically be expressed as the output power divided
by the input power.
η=
POUT
PIN
In addition, with an ideal 1.5X charge pump, the
output current may be expressed as 2/3 of the
3131.2005.12.1.2
Careful selection of the four external capacitors
CIN, C1, C2, 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 general, low ESR
may be defined as less than 100mΩ. A value of
1µF for all four capacitors is a good starting point
when choosing capacitors. 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 recommended over all other types of capacitors for use with
the AAT3131. Ceramic capacitors offer many advantages over their tantalum and aluminum electrolytic
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 connection damage.
11
AAT3131
High Efficiency 1X/1.5X Fractional
Charge Pump for White LED Applications
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
connections, size or area, material composition,
and ambient temperature. Capacitor ESR is typically measured in milliohms for ceramic capacitors
and can range to more than several ohms for tantalum or aluminum electrolytic capacitors.
Ceramic Capacitor Materials
Ceramic capacitors less than 0.1µF are typically
made from NPO or C0G materials. NPO and C0G
materials have tight tolerance and are stable over
temperature. Large capacitor values are typically
composed of X7R, X5R, Z5U, or Y5V dielectric
materials. Large ceramic capacitors, greater than
2.2µF, are often available in low-cost Y5V and Z5U
dielectrics, but capacitors greater than 1µF are
usually not required for AAT3131 applications.
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 AAT3131 has a thermal protection circuit that
will shut down the internal LDO and charge pump if
the die temperature rises above the thermal limit,
as is the case during a short-circuit of the OUT pin.
Driving Multiple LEDs, White LED
Display Module Backlights, and
Individual LEDs Connected in Parallel
The AAT3131 D1 to D4 outputs are true constant
current sources capable of driving up to 20mA (D1
to D3) or 30mA (D4) each over the operation input
voltage range. Since these outputs are true constant current sources, they may be connected in
parallel to drive a single power output. Any combination of outputs (D1 to D4) may be connected in
parallel. The maximum total output current is a sum
of how many current sources are parallel connected. This feature is particularly useful to power premanufactured display modules which are pre-wired
12
with white LED backlights connected in a parallel
circuit configuration. Any combination of outputs
may be connected in parallel to drive groups of
LEDs. The AAT3131 internal current source reference circuit bases feedback from current sensed
on the D1 and D4 outputs. For best operation, the
only requirement for this type of application is the
outputs D1 and D4 should always be connected to
the load circuit.
The AAT3131 may be used to drive multiple LEDs
having differing forward voltages. Using feedback
techniques, the current in D1 to D3 output currents
sources are referenced to the current in the LED
connected to D1. Current source output D4 is its
own reference. If all LEDs are of similar type, the
diodes will be matched in current, maintaining uniform LED brightness despite variations in manufacturer, production, etc.
However, if the diodes are dramatically different in
type comprising a mix of high-VF type and low-VFtype LEDs, the AAT3131 has the capability to optimally and simultaneously drive up to four LEDs of
one type and up to two LEDs of another type. This
feature can be useful for driving different color
LEDs; driving both display backlight and photo-flash
LEDs; or for driving main-LCD and sub-LCD display
LED backlights from a single charge pump IC.
For example, when driving independent RGB
LEDs, the green and blue type LEDs typically
require a high VF to operate (e.g., 3.7V), while the
red LED needs a low forward voltage (e.g., 2V). By
connecting the green and blue diodes to outputs
D1 to D3 and the red diodes to D4, good control
and uniformity in brightness are maintained despite
the 2V difference in the diode forward voltages.
The AAT3131 determines if the 1.5X charge pump
circuit is needed based on the voltage on D1 and
D4, whichever is higher. If adequate voltage is
available to drive the higher voltage LED (of output
D1 or D4) without the charge pump running, the IC
automatically switches into load switch (1X) mode
to maximize efficiency.
Similarly, if a 4V photo-flash LED array is connected to outputs D1 through D3 (with the outputs
shorted together) and two 3.3V sub-LCD display
backlight LEDs are connected to output D4, then
the AAT3131 can optimally drive each set of LEDs
at the programmed current level (see Figure 2).
3131.2005.12.1.2
AAT3131
High Efficiency 1X/1.5X Fractional
Charge Pump for White LED Applications
VIN
C1+
C1
1µF
VOUT
VBATTERY
CIN
COUT
1µF
1µF
D1
D2
D3
D4
RB*
RB*
RB*
RB*
D5
D6
C1C2+
C2
1µF
AAT3131
C2D1
D2
D3
EN/SET
EN/SET
D4
GND
RB*
RB*
*In some applications, white LED forward voltages (VF) 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 approximated by the following equation:
RB =
VSOURCE - VF
IF
Figure 2: AAT3131 Driving Two Groups of Paralleled White LEDs
(e.g., main LCD and sub-LCD backlights).
3131.2005.12.1.2
13
AAT3131
High Efficiency 1X/1.5X Fractional
Charge Pump for White LED Applications
Ordering Information
Package
Marking1
Part Number (Tape and Reel)2
TSOPJW-12
KBXYY
AAT3131ITP-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.
Package Information
TSOPJW-12
2.85 ± 0.20
2.40 ± 0.10
0.10
0.20 +- 0.05
0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC
7° NOM
0.04 REF
0.055 ± 0.045
0.15 ± 0.05
+ 0.10
1.00 - 0.065
0.9625 ± 0.0375
3.00 ± 0.10
4° ± 4°
0.45 ± 0.15
0.010
2.75 ± 0.25
All dimensions in millimeters.
1. XYY = assembly and date code.
2. Sample stock is generally held on part numbers listed in BOLD.
© 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.
Customers are advised 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.
Advanced Analogic Technologies, Inc.
830 E. Arques Avenue, Sunnyvale, CA 94085
Phone (408) 737-4600
Fax (408) 737-4611
14
3131.2005.12.1.2