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CHAPTER 18 STANDBY FUNCTION
(2) Is the input pin level appropriate
The voltage level input to each pin should be in the range between V
SS
potential and V
DD
potential. If a voltage outside
this range is applied, the current consumption will increase and the reliability of the
m
PD784046 may be adversely
affected.
Also ensure that an intermediate potential is not applied.
(3) Are pull-up resistors necessary
An unnecessary pull-up resistor will increase the current consumption and cause a latchup of other devices. A mode
should be specified in which pull-up resistors are used only for parts that require them.
If there is a mixture of parts that do and do not require pull-up resistors, for parts that do, you should connect a pull-
up resistor externally and specify a mode in which the on-chip pull-up resistor is not used.
(4) Is processing of the address bus, address/data bus, etc., appropriate
In STOP mode and IDLE mode, the address bus, address/data bus, RD and LWR, HWR pins become high-
impedance. Normally, these pins are pulled high with a pull-up resistor. If this pull-up resistor is connected to the
backed-up power supply, then if the input impedance of circuitry connected to the non-backed-up power supply is
low, a current will flow through the pull-up resistor, and the current consumption will increase. Therefore, the pull-
up resistor should be connected to the non-backed-up power supply side as shown in Figure 18-6.
Also, in STOP mode and IDLE mode the ASTB pin also becomes high impedance. Countermeasures should be
taken with reference to the points noted in (1).
Figure 18-6. Example of Address/Data Bus Processing
(5) A/D converter
The current flowing to the AV
DD
, AV
REF1
pins can be reduced by clearing (0) the AM0 and AM1 bits of the A/D converter
mode register (ADM). The current can be further reduced, if required, by cutting the current supply to the AV
DD
,
AV
REF
pins with external circuitry.
Make sure that the AV
DD
pin is not at the same potential as the V
DD
pin. Unless power is supplied to the AV
DD
pin
in the STOP mode, not only does the current consumption increase, but the reliability is also affected.
V
DD
V
DD
IN/OUT
CMOS IC, etc.
V
SS
V
SS
Non-Backed-Up Power Supply
ADn
(n = 0-15)
μ
PD784046
Backed-Up Power Supply