STM704 datasheet(9/42 Pages) STMICROELECTRONICS

9 / 42 page

STM690, STM704, STM795, STM802, STM804, STM805, STM806

Description

Doc ID 10519 Rev 9

9/42

1.1

Pin descriptions

1.1.1

MR (manual reset)

A logic low on MR asserts the reset output. Reset remains asserted as long as MR is low

and for trec after MR returns high. This active-low input has an internal pull-up. It can be

driven from a TTL or CMOS logic line, or shorted to ground with a switch. Leave open if

unused.

1.1.2

WDI (watchdog input)

If WDI remains high or low for 1.6 s, the internal watchdog timer runs out and reset is

triggered. The internal watchdog timer clears while reset is asserted or when WDI sees a

rising or falling edge.

The watchdog function cannot be disabled by allowing the WDI pin to float.

1.1.3

RST (active-low reset)

Pulses low for trec when triggered, and stays low whenever VCC is below the reset threshold

or when MR is a logic low. It remains low for trec after either VCC rises above the reset

threshold, the watchdog triggers a reset, or MR goes from low to high.

1.1.4

RST (active-high reset - open drain)

Pulses high for trec when triggered, and stays high whenever VCC is above the reset

threshold or when MR is a logic high. It remains high for trec after either VCC falls below the

reset threshold, the watchdog triggers a reset, or MR goes from high to low.

1.1.5

PFI (power-fail input)

When PFI is less than VPFI or when VCC falls below VSW (2.4 V), PFO goes low; otherwise,

PFO remains high. Connect to ground if unused.

1.1.6

PFO (power-fail output)

When PFI is less than VPFI, or VCC falls below VSW, PFO goes low; otherwise, PFO remains

high. Leave open if unused. Output type is push-pull.

1.1.7

VOUT (supply output voltage)

When VCC is above the switchover voltage (VSO), VOUT is connected to VCC through

a P-channel MOSFET switch. When VCC falls below VSO, VBAT connects to VOUT. Connect

to VCC if no battery is used.

1.1.8

Vccsw (VCC switch output)

When VOUT switches to battery, Vccsw is high. When VOUT switches back to VCC, Vccsw is

low. It can be used to drive gate of external PMOS transistor for IOUT requirements

exceeding 75 mA. Output type is push-pull.

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