HA16117F Series

7

Internal Operation and Usage Notes

Figure 3 shows an equivalent circuit of the watchdog timer block with a V

level of 0 V, and the following pages show internal operation timing charts for different P-RUN

frequencies. (Descriptions apply to conditions C

Operation

The power-on and auto-reset circuit is a multivibrator with timing controlled by C

discharge current I

As I

on-duty is 25% or above, the C

is fixed low, and

RES is not output. The (WD) on-duty varies according to the P-RUN frequency. If the

frequency is lower or higher than the design value, the (WD) on-duty decreases, and at 25% or below,

RES

is output. Refer to the timing charts on the following pages for an explanation of the operation of the

watchdog filter.

Usage Notes

• When the P-RUN frequency reaches 20 kHz or above, t

following pages). This must be borne in mind in the design stage.

• If the P-RUN frequency fluctuates, RES may also be output within the normal detection set frequency

(see the timing charts on the following pages).

• Detection frequencies f

dispersion can be expected. A margin of

±30% or more should be allowed for in the design.

−

+

−

+

−

+

A

0.8

µ

typ

0.01

µ

0.1

µ

P-RUN

1/2

frequency divider

0.9 V

3.6 V

WD

B

C

10.7

µ

typ

8

µ typ

Q

D

φ

Q

3.2 V

1.6 V

Low voltage detection block

Power-on and auto-reset circuit

Watchdog filter circuit

RES

Q

Q

Figure 3 Watchdog Timer Evaliation Circuit