UCC2946

UCC3946

SLUS247F − APRIL 1997 − REVISED NOVEMBER 2007

8

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APPLICATION INFORMATION

CONNECTING WDO TO RES

In order to provide design flexibility, the reset and watchdog circuits in the UCCx946 have separate outputs.

Each output independently drives high or low, depending on circuit conditions explained previously.

In some applications, it may be desirable for either the RES or WDO to reset the microprocessor. This can be

done by connecting WDO to RES. If the pins try to drive to different output levels, the low output level dominates.

Additional current flows from VDD to GND during these states. If the application cannot support additional

current (during fault conditions), RES and WDO can be connected to the inputs of an OR gate whose output

is connected to the microprocessor’s reset pin.

LAYOUT CONSIDERATIONS

A 0.1-

µF capacitor connected from VDD to GND is recommended to decouple the UCCx946 from switching

transients on the VDD supply rail.

with minimal trace length to reduce board capacitance. Care should be taken to route any traces with high

voltage potential or high speed digital signals away from these capacitors.

Resistors R1 and R2 generally have a high ohmic value, traces associated with these parts should be kept short

in order to prevent any transient producing signals from coupling into the high impedance RTH pin.

TYPICAL CHARACTERISTICS

Figure 5.

THRESHOLD RESISTANCE

vs

AMBIENT TEMPERATURE

TA − Ambient Temperature − °C

−55

1.22

1.20

−35

−15

5

25

45

65

85

105

125

1.21

1.25

1.23

1.24

1.26

VDD = 5 V

2

10.0

9.0

345

6

9.5

11.5

10.5

11.0

12.0

Figure 6.

VDD − Input Voltage − V

INPUT CURRENT

vs

INPUT VOLTAGE