AAT1415 Datasheet, PDF (22/32 Pages) Advanced Analog Technology, Inc. – FIVE-CHANNEL DC-DC CONVERTER WITH A 2.5V LDO

Advanced Analog Technology, Inc.
May 2008
AAT1415/AAT1415A
DETAILED DESCRIPTION
The AAT1415/AAT1415A is a complete
power-conversion IC for digital still cameras. It can
accept input from a variety of sources, including
single-cell Li+ batteries and 2-cell alkaline or NiMH
batteries. The AAT1415/AAT1415A includes five
DC-DC converter channels and a 2.5V LDO to
generate all required voltages:
Synchronous-rectified boost or buck DC-DC
converter with on-chip MOSFETs—Typically
supplies 4.6V for lens motor or 3.3V for main
system power.
Synchronous-rectified boost or Buck DC-DC
converter with on-chip MOSFETs— Typically
supplies 3.3V for main system power or 2.5V for
DDR.
Synchronous-rectified buck DC-DC converter with
on-chip MOSFETs— Typically supplies 1.5V for
the DSP core.
Boost controller— Typically used for positive
voltage to bias one or more of the LCD, CCD, and
LED backlights.
Inverter controller— Typically supplies negative
CCD bias when high current is needed for large
pixel-count CCDs.
2.5V LDO— Typically supplies 2.5V for
analog-to-digital converter’s reference voltage.
The AAT1415/AAT1415A includes three versatile
status outputs that can provide information to the
system. All are open-drain outputs and can directly
drive MOSFET switches to facilitate sequencing,
disconnect loads during overloads, or perform
other hardware-based functions.
TR1
TR1 pulls low when EN1 pulls high. A typical use for
TR1 is to reduce CH1 boost feedback network’s
leakage current when CH1 is disabled (Figure 1).
C3RDY
C3RDY pulls low when IN3 reaches V_F13 (1.1V typ).
C3RDY goes high impedance in shutdown, overload,
and thermal limit when IN3 is under V_F13. A typical use
for C3RDY is to enable 3.3V power to the CPU I/O
after the CPU core is powered up (Figure 1), thus
providing safe sequencing in hardware without system
intervention.
C4RDY
C4RDY pulls low when IN4 reaches V_F13 (1.1V typ).
C4RDY goes high impedance in shutdown, overload,
and thermal limit when IN4 is under V_F13. A typical use
for C4RDY is to drive a PMOS that gates 5V power to
the CCD until the VH CCD bias (generated by CH4) is
powered up (Figure 4).
Figure 4. C4RDY Application Circuit
Soft-Start
The AAT1415/AAT1415A channels feature a soft-start
function that limits inrush current and prevent
excessive battery loading at startup by ramping the
output voltage of each channel up to the regulation
voltage.
This is accomplished by ramping the internal reference
inputs to mostly channel error amplifier from 0V to the
1.25V reference voltage (CH5 from 1.25V to 0V) over a
period of 4,096 oscillator cycles (16ms at 500kHz)
when initial power is applied or when a channel is
enabled. Soft-start of CH1 is different from others in
order to avoid limiting startup capability with loading.
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Version 3.00
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