STM6779 datasheet(6/25 Pages) STMICROELECTRONICS

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STM6717/6718/6719/6720/6777/6778/6779*/6780*

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Pin Descriptions

Active-Low, Push-pull Reset Output (RST) -

STM6718/20/78/80. The RST pin is driven low

and stays low whenever VCC1 or VCC2 or RSTIN

falls below its factory-trimmed or adjustable reset

threshold or when MR goes to logic low. It remains

low for trec after ALL supply voltages being moni-

tored rise above their reset thresholds and MR

goes from low to high. (Push-pull outputs are ref-

erenced to VCC1.)

Active-Low, Open Drain Reset Output (RST) -

STM6717/19/77/79. The RST pin is driven low

and stays low whenever VCC1 or VCC2 or RSTIN

falls below its factory-trimmed or adjustable reset

threshold or when MR goes to logic low. It remains

low for trec after ALL supply voltages being moni-

tored rise above their reset thresholds and MR

goes from low to high. Connect an external pull-up

resistor to VCC1. A 10kΩ pull-up resistor should be

sufficient for most applications.

Push-Button Reset Input (MR). When MR goes

low the RST output is driven low. RST remains low

as long as MR is low and for trec after MR returns

to high. This active-low input has an internal 50k

Ω

pull-up resistor to VCC1. It can be driven from a

TTL or CMOS logic line, or with open drain/collec-

tor outputs, or connected to VSS through a switch.

If unused, leave this pin open or connect it to VCC1.

Connect a normally open momentary switch from

MR to VSS; external debounce circuitry is not re-

quired. (If MR is driven from long cables or if the

device is used in noisy environments, connecting

a 0.1µF capacitor from MR to VSS provides addi-

tional noise immunity.

Manual Reset Delay Input (MRC) - STM6777/78/

79/80). This pin is either left open or connected to

VSS via a capacitor. By selecting the appropriate

capacitor, the manual reset process, initiated by

pressing the push-button Manual Reset Input, can

be delayed by any value from 6µs or more (see

Table 7., page 19).

Primary

Supply

Voltage

Monitoring

Input

(VCC1). It also is the input for the primary reset

threshold monitor. Available fixed (customer-se-

lectable, factory-programmed) reset thresholds in-

clude 4.63V to 1.58V.

Secondary Supply Voltage Monitoring Input

(VCC2). This

function

available

the

STM6717/18/19/20/77/78. Fixed

(customer-se-

lectable, factory-programmed) reset thresholds in-

clude 3.08V to 0.79V.

Adjustable Reset Comparator Input (RSTIN;

STM6719/20/79/80). This is a high impedance in-

put. RST is driven low when the voltage at the

RSTIN pin falls below 0.626V (internal reference

voltage at this comparator). The monitored voltage

reset threshold is set with an external resistor-di-

vider network.

Table 3. Pin Functions

Name

Function

STM6717

STM6718

STM6719

STM6720

STM6777

STM6778

STM6779

STM6780

RST

Active-low Reset Output

Push-button Reset Input

–

MRC

Manual Reset Delay Input

VCC1

Primary Supply Voltage Input

4–

VCC2

Secondary Supply Voltage Input

–

RSTIN

Adjustable Reset Comparator Input

VSS

Ground

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