ST72C171 datasheet(132/152 Pages) STMICROELECTRONICS

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ST72C171

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9.9 CONTROL PIN CHARACTERISTICS

9.9.1 Asynchronous RESET Pin

Subject to general operating conditions for VDD, fOSC, and TA unless otherwise specified.

Figure 89. Typical Application with RESET pin 8)

Notes:

1. Unless otherwise specified, typical data are based on TA=25°C and VDD=5V.

2. Data based on characterization results, not tested in production.

3. Hysteresis voltage between Schmitt trigger switching levels. Based on characterization results, not tested.

4. The IIO current sunk must always respect the absolute maximum rating specified in Section 9.2.2 and the sum of IIO

(I/O ports and control pins) must not exceed IVSS.

5. The RON pull-up equivalent resistor is based on a resistive transistor (corresponding ION current characteristics de-

scribed in Figure 90). This data is based on characterization results, not tested in production.

5. To guarantee the reset of the device, a minimum pulse has to be applied to RESET pin.

6. All short pulse applied on RESET pin with a duration below th(RSTL)in can be ignored.

7. The reset network (the resistor and two capacitors) protects the device against parasitic resets, especially in a noisy

environment.

8. The output of the external reset circuit must have an open-drain output to drive the ST7 reset pad. Otherwise the device

can be damaged when the ST7 generates an internal reset (LVD or watchdog).

Symbol

Parameter

Conditions

Min

Typ 1)

Max

Unit

VIL

Input low level voltage 2)

0.3xVDD

VIH

Input high level voltage 2)

0.7xVDD

Vhys

Schmitt trigger voltage hysteresis 3)

400

VOL

Output low level voltage 4)

(see Figure 91, Figure 92)

VDD=5V

IIO=+5mA

0.68

0.95

IIO=+2mA

0.28

0.45

RON

Weak pull-up equivalent resistor 5)

VIN=VSS

VDD=5V

Ω

VDD=3.4V

100

120

tw(RSTL)out Generated reset pulse duration

External pin or

internal reset sources

1/fSFOSC

µs

th(RSTL)in External reset pulse hold time

µs

tg(RSTL)in Filtered glitch duration

100

RESET

VDD

WATCHDOG RESET

ST72XXX

LVD RESET

INTERNAL

RON

0.1

µF

VDD

0.1

µF

VDD

4.7k

Ω

EXTERNAL

RESET

CIRCUIT 8)

RESET CONTROL

USER

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