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PDF AAT2845 Data sheet ( Hoja de datos )
| Número de pieza | AAT2845 | |
| Descripción | Four-Channel Backlight Driver | |
| Fabricantes | ANALOGICTECH | |
| Logotipo |  |
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AAT2845
Four-Channel Backlight Driver with Dual LDOs
General Description
Features
ChargePump™
The AAT2845 is a highly integrated power solution
for single-cell lithium-ion-based LCD display appli-
cations. It includes a four-channel LED backlight
driver and two integrated 200mA LDOs as addi-
tional power supplies for display and camera-relat-
ed chipsets.
The backlight driver is a low noise, constant fre-
quency charge pump DC/DC converter that uses a
tri-mode load switch (1X), fractional (1.5X), and
doubling (2X) conversion to maximize efficiency.
Each of the four channels is capable of driving up
to 20mA per channel.
AnalogicTech's S2Cwire™ (Simple Serial Control™)
serial digital input is used to enable, disable, and
set current for each LED with 16 available settings
down to 50µA. The low current mode supply current
can be as low as 50µA to save power and maintain
high efficiency.
Each LED output is equipped with built-in protec-
tion for short-circuit and auto-disable functions.
Built-in soft-start circuitry prevents excessive
inrush current during start-up. A low current shut-
down feature disconnects the load from VIN and
reduces quiescent current to less than 1µA.
The AAT2845 is available in a Pb-free, thermally-
enhanced 20-pin 3x4mm TQFN package.
• Input Voltage Range: 2.7V to 5.5V
• Four-Channel LED Driver:
— Tri-Mode Charge Pump
— Up to 20mA/Channel
— Easy Control with Single Wire Interface
— 16 Current Levels
— Four Low Current Settings Down to 50µA
— Low IQ (50µA) for Low Current Mode
— >90% Peak Efficiency
• Dual 200mA LDOs
• Automatic Soft-Start
• Over-Temperature Protection
• Available in 3x4mm TQFN34-20 Package
• -40°C to +85°C Temperature Range
Applications
• Camera Function Power Supplies
• Camera Phone Displays
• LCD Modules
• White LED Backlighting
Typical Application
VBAT
3.6V
CIN
2.2µF
S2Cwire Backlight Control
LDO Enable
CBYP
0.1µF
CF1 CF2
1µF 1µF
C1- C1+ C2- C2+
IN OUT
AAT2845
D1
D2
D3
D4
IN LDOA
FBA
EN/SET
ENLDO
LDOB
CBP
GND
FBB
COUT
1µF
200mA
Co1
200mA
Co2
2845.2006.12.1.0
1
1 page  
AAT2845
Four-Channel Backlight Driver with Dual LDOs
Electrical Characteristics1
CIN = CO1 = CO2 = 2.2µF, C1 = C2 = 1.0µF, CBP = 0.1µF; TA = 25°C, unless otherwise noted. Typical values are
at TA = 25°C and VIN = 3.6V.
Symbol
LDOs
Description
IIN IN Operating Current
VFB
VDO
ΔVOUT/
VOUT*ΔVIN
PSRR
Feedback Voltage
Dropout Voltage
Line Regulation
Power Supply Rejection Ratio
LDO Logic Control
VIL
EN/SET, ENLDO Pins Logic
Low Threshold
VIH
EN/SET, ENLDO Pins Logic High
Threshold
Conditions
ENLDO = IN, EN/SET = AGND,
No Load
IOUT = 1mA to 200mA
IOUT = 150mA
VIN = (VOUT + 1V) to 5.0V
IOUT =10mA, 1kHz
Min Typ Max Units
80 150 µA
1.17 1.2 1.23 V
150 300 mV
0.09 %/V
50 dB
0.4 V
1.4 V
1. The AAT2845 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured
by design, characterization, and correlation with statistical process controls.
2845.2006.12.1.0
5
5 Page 
AAT2845
Four-Channel Backlight Driver with Dual LDOs
cuitry is needed to control LED brightness. This
feature greatly reduces the burden on a microcon-
troller or system IC to manage LED or display
brightness, 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 suc-
cessively to brighten or dim LEDs in smooth transi-
tions (e.g., to fade out) or in abrupt steps, giving the
user complete programmability and real-time con-
trol of LED brightness.
The last four codes of the current level scale
engage a reduced quiescent current mode that
enhances the low-current setting efficiency. This
mode is especially useful for low-current applica-
tions where a continuous, low-current state is
maintained for a substantial length of time.
S2Cwire Serial Interface
The current sink magnitude is controlled by
AnalogicTech's S2Cwire serial digital input. The
interface records rising edges of the EN/SET pin
and decodes them into 16 different states. The 16
current level settings available are indicated in
Table 1.
Data
1
2
3
4
5
6
7
8
Output
(mA/Ch)
20
18.9
18.0
17.0
15.7
14.8
10.2
8.0
Data
9
10
11
12
13
14
15
16
Output
(mA/Ch)
6.0
4.2
2.9
2.0
1.0
0.53
0.10
0.05
Table 1: Current Level Settings.
The S2Cwire serial interface has flexible timing.
Data can be clocked-in at speeds higher than
1MHz, or much slower, such as 15kHz. After data
is applied, EN/SET is held high to latch the data.
Once EN/SET has been held in the logic high state
for time TLAT (500µs), the programmed current
becomes active and the internal data register is
reset to zero. For subsequent current level pro-
gramming, the number of rising edges correspon-
ding to the desired code must be applied on the
EN/SET pin. When the EN/SET pin is held low for
an amount of time longer than TOFF (500µs), the
AAT2845 enters shutdown mode and draws less
than 1µA from the input. An internal data register is
reset to zero during shutdown.
Auto-Disable Feature
The charge pump in the AAT2845 is equipped with
an auto-disable feature for each LED channel. After
the IC is enabled and started up, a test current of
100µA (typical) is forced through each sink chan-
nel. The channel will be disabled if the voltage of
that particular DX pin does not drop to a certain
threshold. This feature is convenient for disabling
an unused channel or during an LED fail-short
event.
Low Dropout Regulators
The AAT2845 includes two LDO linear regulators.
The regulators run from the same 2.7V to 5.5V input
voltage as the charge pump. The regulators use a
single on/off control input, ENLDO. The LDO output
voltages are set through a resistive voltage divider
from the output (OUTA or OUTB) to the feedback
input (FBA or FBB). The ratio of resistor values
determines the LDO output voltage. The low 200mV
dropout voltage at 200mA load current allows the
regulator to maintain output voltage regulation.
Each LDO regulator can supply a continuous load
current up to 200mA. Both LDOs include current
limiting and thermal overload protection to prevent
damage to the load or to the LDOs.
Thermal Protection
The charge pump has a built-in thermal protection
circuit that will shut down the charge pump and the
LDOs if the die temperature rises above the ther-
mal limit, as is the case during a short-circuit of the
OUT pin.
2845.2006.12.1.0
11
11 Page | ||
| Páginas | Total 19 Páginas | |
| PDF Descargar | [ Datasheet AAT2845.PDF ] | |
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