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Section 14 Power Supply Circuit
14.1 Overview
The H8/3867 Series 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 1.5 V,
independently 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 1.8 V or above can be held down
to virtually the same low level as when used at approximately 1.5 V. 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.
14.2 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 CV
CC
and V
SS
, as shown in figure 14-1. The internal step-down circuit is made
effective simply by adding this external circuit.
Notes: 1. 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.
2. When the internal power supply step-down circuit is used, operating frequency f
osc
is
0.4 MHz to 2 MHz when V
CC
= 2.2 V to 5.5 V, and 0.4 MHz to 1 MHz otherwise.
3. The LCD power supply and A/D converter analog power supply are not affected by
internal step-down processing.
Figure 14-1 Power Supply Connection when Internal Step-Down Circuit Is Used
CV
CC
V
SS
Internal
logic
Step-down circuit
Internal
power
supply
Stabilization
capacitance
(approx. 0.1
µ
F)
V
CC