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PDF AAT3132A Data sheet ( Hoja de datos )
| Número de pieza | AAT3132A | |
| Descripción | High Efficiency 1.5X Fractional Charge Pump | |
| Fabricantes | AAT | |
| Logotipo |  |
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AAT3132/32A
High Efficiency 1.5X Fractional Charge
Pump for White LED Applications
General Description
Features
ChargePump™
The AAT3132/32A is a low noise, constant frequen-
cy charge pump DC/DC converter that uses frac-
• VIN Range: 2.7V to 5.5V
• <1.0µA of Shutdown Current
tional (1.5X) conversion to maximize efficiency for
• 1MHz Switching Frequency
white LED applications. The device can be used to
• White LED Backlighting
produce current levels up to 20mA in three of its out-
• Fully Independent Display Lighting
puts and up to 25 or 30mA in one of its outputs to
drive LEDs from a 2.7V to 5.5V input. Outputs may
• Drives Low-VF and High-VF Type LEDs
• Up to Three 20mA Outputs
be operated individually or paralleled for driving
• Single 25mA Output (AAT3132-1)
higher-current LEDs. A low external parts count
• Single 30mA Output (AAT3132/32A)
(two 1µF flying capacitors and two small 1µF capac-
• Multi-Position Logarithmic Scale with Digital
itors at VIN and OUT) makes the AAT3132/32A ide-
ally suited for small battery-powered applications.
Control
• Low Noise Constant Frequency Operation
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 loga-
rithmic scales. The AAT3132/32A has a thermal
• Regulated Output Current
• Automatic Soft Start
• No Inductors
• -40°C to +85°C Temperature Range
• 12-Pin TSOPJW Package
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 switch-
Applications
ing frequency enables the use of very small externalwww.DataSheet4U.com
capacitors. A low-current shutdown feature discon-
nects the load from VIN and reduces quiescent cur-
rent to less than 1µA. The device also integrates a
test current/auto-disable feature for each channel.
•
•
•
•
Color (RGB) Lighting
Programmable Current Source
White LED Backlighting
White Photo Flash for Digital Still Cameras
The AAT3132/32A is available in the very small, Pb-
free, 12-pin TSOPJW package.
Typical Application
VBATTERY
CIN COUT
1µF 1µF
EN/SET
VIN C1+
VOUT
C1-
C2+
AAT3132
C2-
EN/SET
D1
D2
D3
D4
GND
C1
1µF
C2
1µF
D5 D4
D3 D2 D1
3132.2005.12.1.4
1
1 page  
AAT3132/32A
High Efficiency 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.
IDIODE vs. Input Voltage
(4x20mA)
VIH and VIL vs. VIN
90
VDIODE = 3.3V VDIODE = 3.4V VDIODE = 3.5V
85 VDIODE = 3.6V
80
0.850
0.825
0.800
75
0.775
VIH
70 0.750
65
60
0.725
0.700
VIL
55 0.675
50 0.650
45 0.625
40 0.600
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
2.5 3.0 3.5 4.0 4.5 5.0 5.5
Input Voltage (V)
Input Voltage (V)
Turn-On to Full-Scale Charge Pump
ENSET
(1V/div)
OUT
(2V/div)
VDIODE
(1V/div)
IIN
(200mA/div)
Time (50µs/div)
ENSET
(1V/div)
VDIODE
(2V/div)
IIN
(100mA/div)
Turn-Off
Time (200µs/div)
3132.2005.12.1.4
Turn-On to Full-Scale Load Switch
ENSET
(1V/div)
OUT
(2V/div)
VDIODE
(2V/div)
IIN
(100mA/div)
Time (50µs/div)
80mA Load Characteristics
VIN
OUT
VDIODE
Time (1µs/div)
5
5 Page 
EN/SET Timing Diagram
EN/SET
Code OFF
AAT3132/32A
High Efficiency 1.5X Fractional Charge
Pump for White LED Applications
tHI
tLO
tOFF
1 23
OFF
Power Efficiency and Device
Evaluation
The charge pump efficiency discussion in the fol-
lowing sections only accounts for efficiency of the
charge pump section itself. Due to the unique circuit
architecture and design of the AAT3132/32A, it is
very difficult to measure efficiency in terms of a per-
cent value comparing input power over output
power.
Since the AAT3132/32A 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.
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
components count, reliability, operating range, and
total energy usage...not just % efficiency.
The AAT3132/32A 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.
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.
3132.2005.12.1.4
η
=
POUT
PIN
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 (η) can be rewritten as:
η = POUT =
PIN
VOUT × IOUT
VIN × 1.5IOUT
=
VOUT
1.5VIN
-or-
η(%)
=
100
⎛
⎝
VOUT ⎞
1.5VIN⎠
For a charge pump with an output of 5V and a nom-
inal 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 agree-
ment 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.
Capacitor Selection
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)
11
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