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AAT3124 Schematic ( PDF Datasheet ) - ETC

Teilenummer AAT3124
Beschreibung High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications
Hersteller ETC
Logo ETC Logo 




Gesamt 18 Seiten
AAT3124 Datasheet, Funktion
AAT3123/4
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
General Description
The AAT3123/24 is a low noise, constant frequen-
cy charge pump DC/DC converter that uses a dual
mode Load Switch (1X) and fractional (1.5X) con-
version to maximize efficiency for White LED appli-
cations. The device can be used to produce current
levels up to 20mA to drive up to 6 LEDs from a
2.7V to 5.5V input. Outputs may be operated indi-
vidually or paralleled for driving higher-current
LEDs. Low external parts counts (two 1µF flying
capacitors and two small 1µF capacitors at VIN,
and OUT) make the AAT3123/24 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 with a 32 level loga-
rithmic scale LED brightness control. The
AAT3123/24 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 circuit-
ry 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 AAT3123 is available in very small
12 pin TSOPJW package. The six output AAT3124
is available in a 16 pin 4x4mm QFN package.
Features
ChargePump
• Dual Mode 1x and 1.5x Charge Pump for
Maximum Efficiency
• Drives Low-VF & High-VF Type LEDs
• Up to 6 20mA Outputs
• 32 Position Logarithmic Scale with Digital
Control
• Simple Serial Control™ (S2Cwire™) interface
• Low Noise Constant Frequency Operation
• 1MHz Switching Frequency
• Small Application Circuit
• Regulated Output Current
• Automatic Soft-Start
• VIN Range: 2.7V to 5.5V
• No Inductors
• Iq < 1µA in Shutdown
• Temperature Range -40 to 85°C.
• 16 pin 4x4 QFN package (AAT3124)
• 12 pin TSOPJW-12 package (AAT3123)
Applications
• White LED Backlighting
• White Photo-Flash for DSCs
• Color (RGB) Lighting
• Programmable Current Source
Typical Application
VBATTERY
VIN C1+
CIN
1µF
COUT
1µF
EN/SET
VOUT
C1-
C2+
AAT3124
C2-
EN/SET
GND
D1
D2
D3
D4
D5
D6
C1
1µF
C2
1µF
D6 D5 D4 D3 D2 D1
3123.2003.09.1.1
1






AAT3124 Datasheet, Funktion
AAT3123/4
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)
OUT
(2V/div)
VDIODE
(1V/div)
IIN
(200mA/div)
50µs/div
ENSET
(1V/div)
OUT
(2V/div)
VDIODE
(2V/div)
IIN
(100mA/div)
50µs/div
Charge Pump to Load Switch (80mA)
VIN
(10mV/div)
OUT
(2V/div)
VDIODE
(2V/div)
IIN
(100mA/div)
50µs/div
ENSET
(1V/div)
VDIODE
(2V/div)
IIN
(100mA/div)
Turn-Off
200µs/div
Load Switch to Charge Pump (80mA)
VIN
(20mV/div)
OUT
(1V/div)
VDIODE
(1V/div)
IIN
(200mV/div)
50µs/div
80mA Load Characteristics
VIN
OUT
VDIODE
1µs/div
6 3123.2003.09.1.1

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AAT3124 pdf, datenblatt
AAT3123/4
High Efficiency 1X/1.5X Fractional Charge
Pump for White LED Applications
If however, the diodes are dramatically different in
type comprising a mix of high-VF type and low-VF-
type LED's, the AAT3124 has the capability to opti-
mally drive up to four LED's of one-type and up to
two LED's of another type simultaneously. Such a
feature can be useful for driving different color
LED's; driving both display backlight and photo-
flash LED's; or for driving main-LCD and sub-LCD
display LED backlights from a single Charge Pump
IC. For example, when driving independent RGB
LED's, the green and blue type LED's 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 D4 and the red diodes to D5 and D6, good
control and uniformity in brightness is maintained
despite the 2V difference in the diode forward volt-
ages. The AAT3124 determines if the 1.5X charge
pump circuit is needed based on the voltage on D1
and D5, which ever one is higher. If adequate volt-
age is available to drive the higher voltage LED (of
output D1 or D5) without the charge pump running,
the IC automatically switches into step down (1X)
mode to maximize efficiency.
Similarly, if a 4V photo-flash LED-array is connect-
ed to outputs D1 through D4 (with the outputs
shorted together) and two 3.3V sub-LCD-display
backlight LED's are connected to outputs D5 and
D6, then the AAT3124 can optimally drive each set
of LED's at the programmed current level (see
application schematics). The photo-flash can be
disabled by an N-channel switch connected in
series with the photo-flash LED.
The AAT3123/24 has only one programmed value
of current and does not allow for separate on/off or
brightness control of each current source output.
This limitation can easily be circumvented by intro-
ducing grounded source N-channel MOSFET
switches in series with the LEDs to turn any given
LED (or bank of LEDs) on or off. The various LEDs
can be turned on and off independently, simultane-
ously, or multiplexed to produce any variety of light-
ing effects. By reprogramming the current source
(via the serial interface) between switching transi-
tions, the brightness of individual LEDs, or banks of
LEDs can also be controlled.
Charge Pump Compatibility
The 4-output AAT3123 is pin-compatible with the
AAT3113 in both QFN and TSOPJW-12 packages.
The six-output AAT3124 is pin compatible with the
AAT3114 in the QFN package. Compared to the
AAT3113/14, the AAT3123/24 offers an improved
overall efficiency, wider operating range, and the
ability to drive high-VF type LED's (up to 4.3V) at
full current from a 3V input condition. The
AAT3123/24 is well suited for battery powered
applications using single-cell lithium-ion (Li-Ion)
batteries (4.2V to 2.8V), lithium polymer batteries,
and 3-series connected dry cells (3.6V).
12 3123.2003.09.1.1

12 Page





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