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VC
M1
VC
Reset Circuit
VB2
XRST(INT)
VBSEL
VB1ON
VB2ON
PWM(DDC)
STATUP-CLK
VGRST
Mode Select and Output Buffer Circuit
INM
VREF
VC
VREF
SAW
DTC
Switching Power Supply operation Circuit
VC
VC
XRST
M2
CRST
XRST
(INT)
RF
PWM OUT
(To OUTPUT BUFFER)
When VC reaches 88% of the expected value, the output of the
comparator becomes L, M1 and M2 go OFF, and as a result
XRST becomes H. The timing can also be delayed using the
capacitor attached externally to CRST.
D1
D0
To MPC17A55
VCON
PWM1
When XRST (INT) is L, as VBSEL is negated, the D0 and D1
logics are determined according to VB1 ON and VB2 ON.
Voltage is output when VGRST becomes H. If VB2 is being
supplied, both D0 and D1 are set to H, and the MPC17A55 is
set into the up-down mode to perform start. After starting,
when XRST (INT) becomes H, if VB2 is above 3.3V, D0 is set
to H and D1 is set to L to set the step-down mode. PWM1
outputs the STARTUP CLK when XRST (INT) is L.
The switching power supply control circuit is composed of the
error amplifier and comparator. The error amplifier extracts the
error voltage from the 1/2 reference voltage of VREF and VC,
and generates PWM from SAW. DTC performs the software-
switching at start and at the same time, limits the PWM duty.
Although the maximum duty is set to 95%, it can be changed
through external settings. In addition, as MPC1830 is not
equipped with the power section required for controlling the
switching power supply, the MPCV17A55 or an external
transistor is required.
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