Cautions On Handling Devices - Fujitsu F2MC-16LX Hardware Manual

1.8

Cautions on Handling Devices

When handling MB90550A/B devices, pay particular attention to the following points:
• Prevention of latchup
• Stabilization of power supply voltage
• Handling unused pins
• Cautions in connection with using an external clock
• Handling power supply pins (Vcc/Vss)
• Crystal oscillator circuit
• Procedure for turning on the A/D converter power supply and the analog input
• Recover from standby
• Cautions on turning on the power supply
• Handling power supply pins of the A/D converter
• Undefined output from port0 or port1
• Using the "DIV A, Ri" and "DIVW A, RWi" instructions
• Using REALOS
• Notes on operation in PLL clock mode
■ Cautions on Handling Devices
❍ Prevention of latchup
In CMOS ICs, latchup may occur when:
• A voltage higher than Vcc or lower than Vss is applied to an input or output pin.
• A voltage which exceeds the rating is applied between Vcc and Vss
• The AVcc power supply is turned on before Vcc voltage is applied
If latchup occurs, power supply current increases rapidly and elements may be damaged by
heat. Pay particular attention when using the device to prevent this.
For the same reason, make sure that the analog power supply current does not exceed the
digital power supply current.
❍ Stabilization of power supply voltage
If the power supply voltage varies acutely even within the operation assurance range of the Vcc
power supply voltage, a malfunction may occur. The Vcc power supply votage must therefore
be stabilized. As stabilization guidelines, stabilize the power supply voltage so that Vcc ripple
fluctuations (peak to oeak value) in the commercial frequencies (50 Hz to 60 Hz) fall within 10%
of the standard Vcc power supply voltage and the transient fluctuation rate becomes 0.1 V/ms
or less in instantaneous fluctuation for power supply switching.
❍ Handling unused pins
Leaving unused input pins open may cause malfunctions or permanent damage due to latchup
of the device. To prevent this problem, use pull-up or pull-down resistors of 2 kΩ or more. If an
input/output pin is not used, set it to output and leave the pin open, or set it to input and handle
it as an input pin.
1.8 Cautions on Handling Devices
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