M5295AFP Просмотр технического описания (PDF) - Renesas Electronics

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M5295AFP

Watchdog Timer

Renesas Electronics 

M5295AL/AP/AFP

• Pin (1) (WD pin) input requirements

(1) Connect capacitor between WD pin and voltage input. (refer to section 3)

(2) Input cycle: tWD or less (discharge should start before voltage at WD pin reaches 4 V.)

1

<f

1.1 ⋅ C ⋅ R1

(3) Input pulse width tWDIN: t2 or less

C = 104

1ms t

C = 103

100µs

t1

VCC = 5V

50µs

0.5

ms

R1 = 10kΩ

t2

2

3

4

Discharge Voltage x(V)

Figure 4

3. Relationship between input pulse width and input capacitance Cin

When input to pin (1) is 1.5 V or more, TC pin discharges electricity. Determine pulse width and input capacitance

Cin with reference to the diagram shown in figure 5.

VIN

30k

1

Q1

Cin

20k

Q1 is off when voltage at pin (1) is 1.5V or less.

t3 = Cin ⋅ 5 × 104 ⋅ ln

Vin

1.5

RST1 is output when t4 is longer than tWD.

Vin

VIN

t4

t

WD Vin

(1) 1.5V

t3

TC

t

4V

(2)

tWD

2V

t

RST1

(3)

t

Cin: 10000pF, t3 = 0.6ms

Cin: 1000pF, t3 = 60µs

Cin: 100pF, t3 = 6µs

When t3 is too long, TC pin output waveform frequency changes

as shown above. Set t3 to be sufficiently long to turn on Q1

[tWDIN(3µs) or more] but not to exceed t2 (discharge time).

(t2: Discharge time during normal input)

Figure 5

REJ03D0780-0200 Rev.2.00 Jun 15, 2007

Page 6 of 12

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