AAT3123 ETC, AAT3123 Datasheet - Page 12

• Manufacturer Part Number: AAT3123
• Description: High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications
• Manufacturer: ETC

If however, the diodes are dramatically different in
type comprising a mix of high-V
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 V
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
12
F
to operate (e.g. 3.7V) while the
F
type and low-V
High Efficiency 1X/1.5X Fractional Charge
F
-
Pump for White LED Applications
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-V
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).
F
type LED's (up to 4.3V) at
3123.2003.09.1.1