
20
CHAPTER 2 HANDLING DEVICE
2.1
Notes on Handling Pins and Circuits
This section describes latchup prevention, pin processing, and circuit handling.
s Latchup Prevention
In CMOS ICs, latchup can occur when voltage greater than the VCC or less than the VSS is
applied to an input or output pin. Latchup also occurs when voltage exceeding the voltage
rating is applied between the VCC and VSS. If latchup occurs, the power supply current may
suddenly increase and damage the circuit elements. Therefore, when using CMOS ICs, do not
to exceed the maximum standard rating.
s Pin Handling
r Handling of unused input pins
Because keeping unused pins open might result in incorrect operation, apply pull-up or pull-
down to control unused input pins.
r Handling of NC pins
Always open and use NC pins.
r Handling of output pins
An output pin can be short-circuited with the power supply or with another output pin, or can
carry a large current when connected to a high capacity load.
If any of this occurs for an
extended period, the device may be damaged. Therefore, always ensure that the maximum
standard rating is not exceeded.
r Handling of power supply pins
When several VCC and VSS elements are used, device design will ensure that VCC and VSS
elements that should have the same potential are connected internally to prevent incorrect
operations such as latchup. However, these elements must always be connected to the power
supply and ground externally: This is for reducing unnecessary radiation, preventing incorrect
operation of the strobe signals due to an increase in ground voltage, and for maintaining the
total output current rating.
In addition, ensure that the impedance remains as low as possible when connecting the VCC
and VSS elements of the device with the central power supply.
Moreover, it is recommended that a ceramic capacitor of about 0.1
F be connected between
the VCC and VSS as a bypass capacitor.
r Handling of mode pins (MD0 to MD2)
Connect the mode pins directly to the VCC or VSS. In addition, to prevent the test mode from
being set because of noise, shorten the pattern length between the mode pins on the PC board
and the VCC or VSS as much as possible and connect the elements with low impedance.