STM6905 datasheet(7/19 Pages) STMICROELECTRONICS

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STM6905

Pin descriptions

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Pin descriptions

2.1

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. The active-low input has an internal 10k ohm pull-up

resistor to VCC. It can be driven from a TTL or CMOS logic line, or with open drain/collector

outputs, or connected to VSS through a switch. If unused, leave this pin open or connect it to

VCC.

Connect a normally open momentary switch from MR to VSS; external debounce circuitry is

not required. (If MR is driven from long cables or if the device is used in noisy environments,

connecting a 0.1uF capacitor from MR to VSS provides additional noise immunity).

2.2

VCC primary supply voltage monitoring input

The VCC pin is also the input for the primary reset threshold monitor. Fixed (customer-

selectable, factory programmed) reset thresholds include 3.078 V to 2.866 V.

2.3

V2IN second fixed voltage monitoring input

The V2IN input is the second fixed-voltage input for reset threshold monitoring. Available

fixed (customer-selectable, factory programmed) reset thresholds include 2.333 V to

1.050 V.

2.4

VSS

This pin is the ground pin for the power supply.

2.5

V3IN, V4IN, and V5IN

The V3IN, V4IN and V5IN are high impedance inputs. RST is driven low when the voltage

(VTRIP) at the pin falls below 600 mV (internal reference voltage at their respective

comparators). The monitored voltage reset threshold is set with an external resistor-divider

network.

2.6

RST active-low, open drain reset output

The reset output (RST) pin is driven low and stays low whenever VCC or V2IN, or V3IN, or

V4IN, or V5IN 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 monitored rise above

their reset thresholds and MR goes from low to high. Connect an external pull-up resistor to

VCC. A 10k ohms pull-up resistor should be sufficient for most applications.

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