TMP93CS40DF datasheet(36/48 Pages) TOSHIBA

36 / 48 page

Quality and Reliability Assurance / Handling Precautions

030901

QUA-36

2002-02-20

4.3.4

Unused Pins

If unused pins are left open, some devices can exhibit input instability

problems, resulting in malfunctions such as abrupt increase in current flow.

Similarly, if the unused output pins on a device are connected to the power

supply pin, the ground pin or to other output pins, the IC may malfunction or

break down.

Since the details regarding the handling of unused pins differ from device to

device and from pin to pin, please follow the instructions given in the relevant

individual datasheets or databook.

CMOS logic IC inputs, for example, have extremely high impedance. If an

input pin is left open, it can easily pick up extraneous noise and become

unstable. In this case, if the input voltage level reaches an intermediate level,

it is possible that both the P-channel and N-channel transistors will be turned

on, allowing unwanted supply current to flow. Therefore, ensure that the

unused input pins of a device are connected to the power supply (Vcc) pin or

ground (GND) pin of the same device. For details of what to do with the pins of

heat sinks, refer to the relevant technical datasheet and databook.

4.3.5

Latch-up

Latch-up is an abnormal condition inherent in CMOS devices, in which Vcc

gets shorted to ground. This happens when a parasitic PN-PN junction

(thyristor structure) internal to the CMOS chip is turned on, causing a large

current of the order of several hundred mA or more to flow between Vcc and

GND, eventually causing the device to break down.

Latch-up occurs when the input or output voltage exceeds the rated value,

causing a large current to flow in the internal chip, or when the voltage on the

Vcc (Vdd) pin exceeds its rated value, forcing the internal chip into a

breakdown condition. Once the chip falls into the latch-up state, even though

the excess voltage may have been applied only for an instant, the large current

continues to flow between Vcc (Vdd) and GND (Vss). This causes the device to

heat up and, in extreme cases, to emit gas fumes as well. To avoid this problem,

observe the following precautions:

(1)

Do not allow voltage levels on the input and output pins either to rise

above Vcc (Vdd) or to fall below GND (Vss). Also, follow any prescribed

power-on sequence, so that power is applied gradually or in steps rather

than abruptly.

(2)

Do not allow any abnormal noise signals to be applied to the device.

(3)

Set the voltage levels of unused input pins to Vcc (Vdd) or (GND) Vss.

(4)

Do not connect outputs to one another.

4.3.6

Input/Output Protection

Wired-AND configurations, in which outputs are connected together, cannot

be used, since this short-circuits the outputs. Outputs should, of course, never

be connected to Vcc (Vdd) or GND (Vss).

Furthermore, ICs with tri-state outputs can undergo performance degradation

if a shorted output current is allowed to flow for an extended period of time.

Therefore, when designing circuits, make sure that tri-state outputs will not

be enabled simultaneously.

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