Epson LQ-2550 Technical Manual page 109

2.3.4.1 Reference Voltage Supply Circuit
Figure 2-57 shows the circuit that supplies reference voltage
in the sub CPU. In this circuit, programmable shunt regulatorTL431 (9C) is used to output the reference
voltage.
Reference voltage
w h e r e , 2 [p,A]
Iref =
As shown by the above expression,
\ R71
AV
CC
SUB
.. >
AV
SS
Figure 2-57. Reference Voltage Supply Circuit
A/D converter is determined by the combination of resistors R72 and
for the
TL431.
the
is regulated to approximately 4.746 ~].
2-63
VDC) to
the A/D converter