Circuit - Casio CASSIOPEIA A-20 Service Manual & Parts List

3 V Circuit
DC/DC converter MAX608ESA (IC106) generates +3.77 V and it makes up 3 V system.
V3MAIN : The reference voltage for the detector.
V3SYS : +3.4 V source for IC1,IC3,IC5.
V3RAM : +3.4 V source for DRAM (RAM5 ~ RAM8).
V3ROM : +3.4 V source for ROM (U301,U302).
ONSTATUSB : Controls ON/OFF of V3ROM. From pin 99 of CPU.
V3IRDA : +3.4 V source for IrDA Transceiver CIM-10S (IC4).
PIRB : Controls ON/OFF of V3IRDA. From pin 75 of MB87A915 (IC3).
VSUB : +2.7 V source for detecting memory backup battery.
V3AUD : +3.4 V source for MB87A195 (IC3).
PDMMYM : Controls ON/OFF of the load at detecting voltage.
L103
Primary Circuit
SHDN EXT
V+
MAX608 (IC106)
CS
DC-DC converter
D103
Q110
Q108
VIN EXT
VOUT
IC108
3.4 V Regulator
PDMMYM
(Normally L)
— 37 —
Q122
Q123
Q112
CR2032
V3MAIN
V3SYS
V3AUD
V3RAM
V3ROM (To ROM)
ONSTATUSB
OFF: H
ON: L
V3IRDA
(To IrDA)
PIRB
(Normally H)
VSUB