AT1396A/B/C/D
Preliminary Product Information
6-Channel DC-DC Converter for DSC
Auxiliary Controller (CH4,CH5,CH6)
The three auxiliary controllers operate as fixed-frequency voltage-mode PWM
controllers. They use the external MOSFETs, so output power is determined by
external components. All of auxiliary controllers have a guaranteed duty cycle of
minimum duty cycle of 85%(boost-type) or 100%(buck/inverting type). In boost
designs that employ continuous current (CCM), the maximum duty cycle limits the
boost ratio so:
VIN
1−
≤ 85%
VOUT
With discontinuous inductor current(DCM), no such limit exists for the input/output
ratio since the inductor has time to fully discharge before the next cycle begins. The
discontinuous conduction mode boost voltage conversion relationship is given by:
4 × D2
1+ 1+
K
D = K × M × (M − 1)
VO = Vi ×
2
Where K is defined as:
VO
M =
Vi
2 × L
K =
R ×TS
The CH4 is selectable DC/DC controller for drive N-channel MOSFETs (SEL=high)
or P-channel MOSFETs (SEL=low). It can be configure as the inverting circuit
(Figure 2), typically for CCD and LCD bias. This is useful in height-Limited designs
where transformers may not be desired. The efficiency is more than the charge-pump
inversion for some load conditions.
The CH5 can be configure as a switching-mode boost current source for white LEDs,
FB5(0.2V) provides current-sensing feedback, while FB5H(1.0V) provides (optional)
open-LED over-voltage protection(Figure 3). If used as a boost converter, FB5H is
grounded and FB5(0.8V) is used as the feedback input. In this case, CH5 behaves
exactly like CH4 and CH6.
The CH6 can be used for conventional DC/DC boost and flyback designs.(Figure
4 ,Figure 5 and Figure 6)
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4/2/2007 REV:1.1
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