NOTES FOR CMOS DEVICES
1
VOLTAGE APPLICATION WAVEFORM AT INPUT PIN
Waveform distortion due to input noise or a reflected wave may cause malfunction. If the input of the
CMOS device stays in the area between VIL (MAX) and VIH (MIN) due to noise, etc., the device may
malfunction. Take care to prevent chattering noise from entering the device when the input level is fixed,
and also in the transition period when the input level passes through the area between VIL (MAX) and
VIH (MIN).
HANDLING OF UNUSED INPUT PINS
2
Unconnected CMOS device inputs can be cause of malfunction. If an input pin is unconnected, it is
possible that an internal input level may be generated due to noise, etc., causing malfunction. CMOS
devices behave differently than Bipolar or NMOS devices. Input levels of CMOS devices must be fixed
high or low by using pull-up or pull-down circuitry. Each unused pin should be connected to VDD or GND
via a resistor if there is a possibility that it will be an output pin. All handling related to unused pins must
be judged separately for each device and according to related specifications governing the device.
3
PRECAUTION AGAINST ESD
A strong electric field, when exposed to a MOS device, can cause destruction of the gate oxide and
ultimately degrade the device operation. Steps must be taken to stop generation of static electricity as
much as possible, and quickly dissipate it when it has occurred. Environmental control must be
adequate. When it is dry, a humidifier should be used. It is recommended to avoid using insulators that
easily build up static electricity. Semiconductor devices must be stored and transported in an anti-static
container, static shielding bag or conductive material. All test and measurement tools including work
benches and floors should be grounded. The operator should be grounded using a wrist strap.
Semiconductor devices must not be touched with bare hands. Similar precautions need to be taken for
PW boards with mounted semiconductor devices.
4
STATUS BEFORE INITIALIZATION
Power-on does not necessarily define the initial status of a MOS device. Immediately after the power
source is turned ON, devices with reset functions have not yet been initialized. Hence, power-on does
not guarantee output pin levels, I/O settings or contents of registers. A device is not initialized until the
reset signal is received. A reset operation must be executed immediately after power-on for devices
with reset functions.
5
POWER ON/OFF SEQUENCE
In the case of a device that uses different power supplies for the internal operation and external
interface, as a rule, switch on the external power supply after switching on the internal power supply.
When switching the power supply off, as a rule, switch off the external power supply and then the
internal power supply. Use of the reverse power on/off sequences may result in the application of an
overvoltage to the internal elements of the device, causing malfunction and degradation of internal
elements due to the passage of an abnormal current.
The correct power on/off sequence must be judged separately for each device and according to related
specifications governing the device.
6
INPUT OF SIGNAL DURING POWER OFF STATE
Do not input signals or an I/O pull-up power supply while the device is not powered. The current
injection that results from input of such a signal or I/O pull-up power supply may cause malfunction and
the abnormal current that passes in the device at this time may cause degradation of internal elements.
Input of signals during the power off state must be judged separately for each device and according to
related specifications governing the device.
3
Application Note U17121EJ1V1AN
NEC [ NEC ]
