Datasheet

Section 25 Power Supply Circuit
Rev. 6.00 Mar. 18, 2010 Page 803 of 982
REJ09B0054-0600
Section 25 Power Supply Circuit
25.1 Overview
The H8S/2258 Group, H8S/2238B, and H8S/2236B 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, 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 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.
The H8S/2239 Group, H8S/2238R, H8S/2236R, H8S/2237 Group, and H8S/2227 Group do not
have an on-chip internal power supply voltage step-down circuit.
An external power supply should be connected to the V
CC
and CV
CC
pins.
25.2 Power Supply Connection for H8S/2258 Group, H8S/2238B, and
H8S/2236B (On-Chip 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 25.1. The internal step-down circuit is made
effective simply by adding this external circuit. Permanent damage on the chip may result if the
absolute maximum rating of CV
CC
4.3 V is exceeded. Must not connect the external power supply
to the CV
CC
pin.
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. The A/D converter and D/A converter analog power supply are not affected by internal
step-down processing.