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CHAPTER 2 HANDLING DEVICES
2.1
Notes on Handling Devices
This section lists points to note regarding the power supply voltage, pins, and other
device handling aspects.
s Notes on Handling Devices
r Take great care not to exceed the maximum rated voltage (prevent latchup).
Latchup may occur on CMOS ICs if voltage higher than VCC or lower than VSS is applied to
input and output pins other than medium- to high-voltage pins, or if voltage higher than the
ratings is applied between VCC and VSS.
When latchup occurs, power supply current increases rapidly and might thermally damage
elements. When using, take great care not to exceed the absolute maximum ratings.
Also, take care to prevent the analog power supply (AVCC and AVR) and analog input from
exceeding the digital power supply (VCC) when the analog system power supply is turned on
and off.
r Stabilizing supply voltage is important.
A rapid fluctuation of VCC power supply voltage could cause malfunctions, even if it occurs
within the operation assurance range of the voltage.
As stabilization guidelines, it is
recommended to control power so that VCC ripple fluctuations (P-P value) will be less than 10%
of the standard VCC value at the commercial frequency (50 to 60 Hz) and the transient
fluctuation rate will be less than 0.1 V/ms at the time of a momentary fluctuation such as when
power is switched.
r Treatment of unused input pins
Leaving unused input pins open could cause malfunctions. They should be connected to a pull-
up or pull-down resistor.
r Treatment of N.C. pins
Be sure to leave (internally connected) N.C. pins open.
r Treatment of power supply pins on microcontroller with A/D or D/A converters
Connect to be AVCC = DAVC = VCC and AVSS = AVR = VSS even if the A/D and D/A converters
are not in use.
r Precautions when using an external clock
Even when an external clock is used, oscillation stabilization delay time is required for power-on
reset (optional) and wake-up from stop mode.
r Treatment of two Vss pins
Two Vss pins should be connected together externally.