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PDF AAT3131 Data sheet ( Hoja de datos )
| Número de pieza | AAT3131 | |
| Descripción | High Efficiency 1X/1.5X Fractional Charge Pump | |
| Fabricantes | AAT | |
| Logotipo |  |
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AAT3131
High Efficiency 1X/1.5X Fractional
Charge Pump for White LED Applications
General Description
Features
ChargePump™
The AAT3131 is a low noise, constant frequency
charge pump DC/DC converter that uses a dual
• VIN Range: 2.7V to 5.5V
• <1.0µA of Shutdown Current
mode load switch (1X) and fractional (1.5X) con-
• 1MHz Switching Frequency
version to maximize efficiency for white LED appli-
• White LED Backlighting
cations. The device can be used to produce cur-
• Fully Independent Display Lighting
rent levels up to 20mA in three of its outputs and
• Dual Mode 1X and 1.5X Charge Pump for
30mA in one of its outputs to drive LEDs from a
Maximum Efficiency
2.7V to 5.5V input. Outputs may be operated indi-
vidually or paralleled for driving higher-current
• Drives Low-VF and High-VF Type LEDs
• Up to Three 20mA Outputs
LEDs. A low external parts count (two 1µF flying
• Single 30mA Output
capacitors and two small 1µF capacitors at VIN and
OUT) makes the AAT3131 ideally suited for small
• Multi-Position Logarithmic Scale with Digital
Control
battery-powered applications.
• 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 AAT3131 has a thermal man-
• Regulated Output Current
• Automatic Soft Start
• No Inductors
• Temperature Range: -40°C to +85°C
• 12-Pin TSOPJW Package
agement system to protect the device in the event of
a short-circuit condition at the output pin. Built-in
soft-start circuitry prevents excessive
during start-up. A high charge pump
inrush current
switching fre-www.DataSheet4U.com
Applications
quency enables the use of very small external
capacitors. A low-current shutdown feature discon-
nects the load from VIN and reduces quiescent cur-
rent to less than 1µA. The AAT3131 is available in
a Pb-free 12-pin TSOPJW12 package and is rated
• Color (RGB) Lighting
• Programmable Current Source
• White LED Backlighting
• White Photo Flash for Digital Still Cameras
over the -40°C to +85°C temperature range.
Typical Application
VBATTERY
CIN COUT
1µF 1µF
EN/SET
VIN C1+
VOUT
C1-
C2+
AAT3131
C2-
EN/SET
D1
D2
D3
D4
GND
C1
1µF
C2
1µF
D5 D4
D3 D2 D1
3131.2005.12.1.2
1
1 page  
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.
Efficiency vs. Input Voltage
(4x20mA)
100
95
90 VDIODE = 3.3V
85 VDIODE = 3.4V
80
75
70 VDIODE = 3.5V
65 VDIODE = 3.6V
60
55
50
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
Input Voltage (V)
IDIODE vs. Input Voltage
(4x20mA)
90
VDIODE = 3.3V VDIODE = 3.4V VDIODE = 3.5V
85 VDIODE = 3.6V
80
75
70
65
60
55
50
45
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
5.1
Input Voltage (V)
Quiescent Current vs. Input Voltage
VIH and VIL vs. VIN
2.4 0.850
2.2
2.0
1.8
1.6
1.4
1.2 VDIODE = 3.3V
1.0 VDIODE = 3.4V
0.825
0.800
0.775
0.750
0.725
0.700
VIH
VIL
0.8 VDIODE = 3.5V
0.6
0.4
VDIODE = 3.6V
0.2
0.675
0.650
0.625
0.0 0.600
2.50
3.00
3.50
4.00
4.50
5.00
5.50
2.5 3.0 3.5 4.0 4.5 5.0 5.5
Input Voltage (V)
VIN (V)
3131.2005.12.1.2
5
5 Page 
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.
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 volt-
age across the load connected to the constant cur-
rent source outputs. When in load switch mode,
the voltage conversion efficiency is defined as out-
put power divided by input power:
η
=
POUT
PIN
The expression to define the ideal efficiency (η)
can be rewritten as:
η
=
POUT
PIN
=
VOUT × IOUT
VIN × IOUT
=
VOUT
VIN
-or-
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 efficien-
cy (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
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, 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)
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 lev-
els, 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 AAT3131. Ceramic capacitors offer many advan-
tages 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
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| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet AAT3131.PDF ] | |
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