ISSUE 3 - FEBRUARY 2001

ZXCM209

ZXCM210

APPLICATIONS INFORMATION

Negative going V

The ZXCM209/210 are, to a good degree, immune to

short duration negative going supply transients. Under

certain circumstances very brief transients are allowed

without inappropriate false triggering of the reset

circuit. The response to supply transients is shown in the

Noise Immunity graph in the typical characteristics. The

graph indicates the typical allowable transient duration

for a specified threshold overdrive such that a reset

pulse is not generated. Addition of a bypass capacitor,

e.g. 0.1µF, as close as possible to the V

extra transient immunity.

Reset valid down to very low supply voltages

With V

CC

between 0V and 1V the output of the

ZXCM209/210 may be in an undefined state. In many

systems

this

is

inconsequential

as

the

microprocessor, and other circuits, will be inoperative

with supplies this low. In applications where this is

important, the addition of an external resistor ensures

that the reset output remains valid for V

resistor value is non critical: a value of 100k

Ω is

recommended. For the ZXCM209 the resistor should

be applied between reset output and ground: for the

ZXCM210 between reset output and V

Figure 1

shows the connection diagram for the ZXCM devices

in these configurations.

v

cc

ZXCM210

Reset

Output

Gnd

v

cc

Micro

Reset

Input

Gnd

v

cc

100k

v

cc

ZXCM209

Reset

Output

Gnd

v

cc

Micro

Reset

Input

Gnd

v

cc

100k

Figure 1

Circuit for operation of ZXCM with reset valid down to very low supply voltage.

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