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PDF AAT2805 Data sheet ( Hoja de datos )
| Número de pieza | AAT2805 | |
| Descripción | Dual High Efficiency Charge Pump | |
| Fabricantes | AAT | |
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AAT2805
Dual High Efficiency Charge Pump
for White LED and Flash Applications
General Description
Features
ChargePump™
The AAT2805 is a dual charge pump designed to
support both the white LED backlight and flash appli-
• VIN Range: 2.7V to 5.5V
• Dual Charge Pump to Support Backlight and
cations for systems operating with lithium-ion/poly-
Flash LEDs
mer batteries. The backlight charge pump is capable
• Backlight Charge Pump:
of driving up to four LEDs at a total of 120mA. The
— Regulated Current
current sinks may be operated individually or in par-
— Four Current Sink Inputs
allel for driving higher current LEDs. To maximize
— AS2Cwire Brightness Control
power efficiency, the charge pump operates in 1X,
— Tri-Mode Charge Pump
1.5X, or 2X mode, where the mode of operation is
— Maximum 30mA of Current Per Input
automatically selected by comparing the forward
voltage of each LED with the input voltage.
— Low IQ (50µA) in Light Load Mode
• Flash Charge Pump:
AnalogicTech's AS2Cwire™ (Advanced Simple Serial
— Regulated Output Voltage
Control™) serial digital input is used to enable, dis-
— Up to 250mA of Pulsed Current
able, and set current for each LED with a 16-level
• Independent Backlight/Flash Control
logarithmic scale plus four low-current settings down
• Low Noise 1MHz Constant Frequency
to 50µA for optimized efficiency, with a typical oper-
Operation
ating quiescent current of less than 50µA.
• Automatic Soft-Start
The flash charge pump is a charge pump doubler
with a regulated output voltage. It is designed to
• No Inductors
• Available in TDFN44-16 Package
deliver 120mA of continuous current and up to
250mA of pulsed current. It has an independent
enable pin for improved power savings.
www.DataSheet4U.com
The AAT2805 has thermal protection and built-in
Applications
soft-start circuitry. A low-current shutdown feature
disconnects the load from VIN and reduces quiescent
current to less than 1µA.
• Color (RGB) Lighting
• White LED Backlighting
• White LED Photo Flash
The AAT2805 is available in a space-saving, ther-
mally-enhanced TDFN44-16 package and is rated
over the -40°C to +85°C temperature range.
Typical Application
VIN CIN
1µF
EN/SET
EN_FLSH
C1 C2 C3
1µF 1µF 1µF
C1+ C1- C2+ C2- C3+ C3-
VOUT_FL
VIN
AAT2805
VOUT_BL
EN/SET
EN_FLSH
GND
D1
D2
D3
D4
VOUT_FLASH
COUT
1µF
Flash
Backlight
D1 D2 D3 D4
COUT
1µF
2805.2005.05.1.2
1
1 page  
AAT2805
Dual High Efficiency Charge Pump
for White LED and Flash Applications
Typical Characteristics–Flash Driver Charge Pump Section
Output Voltage vs. Output Current
(VOUT_FL = 4.5V; EN_FL = VIN; EN/SET = GND)
4.60
4.56
4.52 3.6V
4.48
4.44
4.40
0.1
3.0V 3.3V
2.7V
1.0
10.0
100.0
Output Current (mA)
1000.0
Maximum Current Pulse vs. Supply Voltage
(VOUT_FL = 4.5V; EN_FL = VIN; EN/SET = GND)
450
One-shot pulse duration = 250ms
400 VOUT > 4.0V
350
300
250
200
150
100
50
0
3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0 4.1 4.2
Supply Voltage (V)
EN_FLSH
(1V/div)
Startup Time
(50mA Load)
EN_FLSH
(1V/div)
Startup Time
(100mA Load)
VOUT_FL
(1V/div)
100µs/div
VOUT_FL
(1V/div)
100µs/div
Load Response vs. Time
(50mA Load)
VOUT_FL
(10mV/div)
VIN = 3.5V
IOUT
(20mA/div)
5ms/div
Load Response vs. Time
(100mA Load)
VIN = 3.5V
VOUT_FL
(10mV/div)
IOUT
(50mA/div)
5ms/div
2805.2005.05.1.2
5
5 Page 
AAT2805
Dual High Efficiency Charge Pump
for White LED and Flash Applications
The AAT2805 requires six external components:
three 1µF ceramic capacitors for the charge pump
flying capacitors (C1, C2 and C3), one 1µF ceramic
input capacitor (CIN), one 0.33µF to 1µF ceramic
capacitor for backlight charge pump output capacitor
(COUT), and one 1µF ceramic capacitor for flash
charge pump output capacitor (COUT).
Constant Current Output Level Settings
The constant current level for the LED channels is set
via the AS2Cwire serial interface according to a loga-
rithmic scale. The current level spacing is 1dB
between adjacent constant current settings. In this
manner, LED brightness appears to change linearly
when the settings are traversed. Because the inputs
D1 to D4 are true independent constant current
sinks, the voltage observed on any single given input
will be determined by the difference between VOUT
and the actual forward voltage (VF) of the LED being
driven.
Since the constant current levels are programmable,
no PWM (pulse width modulation) or additional con-
trol circuitry is needed to control LED brightness. This
feature greatly reduces the burden on a microcon-
troller or system IC to manage LED or display bright-
ness, allowing the user to "set it and forget it." With its
high-speed serial interface (>1MHz data rate), the
LED current drive 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 bright-
ness.
For each Max Current scale (see Table 1), there are
16 current level settings separated from one another
by approximately 1dB. Code 1 is full-scale current
and Code 15 is full-scale current attenuated by
roughly 14dB. Code 16 is reserved as a "no current"
setting. When programming the charge pump, it will
default to the 20mA maximum scale.
The AAT2805 offers an additional Low Current mode
with reduced quiescent current (see Table 2). This
mode is especially useful for low-current applications
where a continuous, low current state is maintained.
The reduction in quiescent current significantly
reduces the impact due to maintaining a continuous
backlighting state.
Data
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
20mA
20.0
17.8
15.9
14.3
12.7
11.1
10.2
8.9
7.9
7.0
6.3
5.7
5.1
4.4
4.1
0.0
Max IOUT (mA)
30mA
30.0
26.7
23.8
21.4
19.0
16.7
15.2
13.3
11.9
10.5
9.5
8.6
7.6
6.7
6.2
0.0
15mA
15.0
13.3
11.9
10.7
9.5
8.3
7.6
6.7
6.0
5.2
4.8
4.3
3.8
3.3
3.1
0.0
Table 1: Constant Current Programming Levels.
Data
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
D1-D3 (mA)
0
0
0
0
0
0
0
0
0.05
0.5
1
2
0.05
0.5
1
2
D4 (mA)
0
0
0
0
0.05
0.5
1
2
0
0
0
0
0.05
0.5
1
2
Table 2: Low Current Register Settings.
2805.2005.05.1.2
11
11 Page | ||
| Páginas | Total 17 Páginas | |
| PDF Descargar | [ Datasheet AAT2805.PDF ] | |
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