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Rev. 1.0, 07/01, page 273 of 372
Section 18 Power Supply Circuit
This LSI incorporates an internal power supply step-down circuit. Use of this circuit enables the
internal power supply to be fixed at a constant level of approximately 3.0 V, regardless of the
voltage of the power supply connected to the external V
CC
pin. As a result, the current consumed
when an external power supply is used at 3.0 V or above can be held down to virtually the same
low level as when used at approximately 3.0 V. If the external power supply is 3.0 V or below, the
internal voltage will be practically the same as the external voltage. It is, of course, also possible
to use the same level of external power supply voltage and internal power supply voltage without
using the internal power supply step-down circuit.
18.1 When Using the Internal Power Supply Step-Down Circuit
Connect the external power supply to the V
CC
pin, and connect a capacitance of approximately 0.1
µF between V
CL
and V
SS
, as shown in figure 18-1. The internal step-down circuit is made effective
simply by adding this external circuit. In the external circuit interface, the external power supply
voltage connected to V
CC
and the GND potential connected to V
SS
are the reference levels. For
example, for port input/output levels, the V
CC
level is the reference for the high level, and the V
SS
level is that for the low level. The A/D converter analog power supply is not affected by internal
step-down processing.
V
CL
V
SS
Internal
logic
Step-down circuit
Internal
power
supply
Stabilization
capacitance
(approx. 0.1 µF)
V
CC
V
CC
= 3.0 to 5.5 V
Figure 18-1 Power Supply Connection when Internal Step-Down Circuit is Used
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