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STM795RDS6F

3V Supervisor with Battery Switchover

STMicroelectronics 

STM690/704/795/802/804/805/806

Pin Descriptions

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 short-

ed to ground with a switch. Leave open if unused.

WDI (Watchdog Input). If WDI remains high or

low for 1.6sec, 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 al-

lowing the WDI pin to float.

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.

RST (Active-high Reset - Open Drain). Pulses

high for trec when triggered, and stays high when-

ever 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.

PFI (Power-fail Input). When PFI is less than

VPFI or when VCC falls below VSW (2.4V), PFO

goes low; otherwise, PFO remains high. Connect

to ground if unused.

PFO (Power-fail Output). When PFI is less than

VPFI, or VCC falls below VSW, PFO goes low; oth-

erwise, PFO remains high. Leave open if unused.

VOUT (Supply Output Voltage). When VCC is

above the switchover voltage (VSO), VOUT is con-

nected 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.

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 75mA.

E (Chip Enable Input). The input to the chip-en-

able gating circuit. Connect to ground if unused.

ECON (Conditional Chip Enable). ECON goes

low only when E is low and reset is not asserted. If

ECON is low when reset is asserted, ECON will re-

main low for 15µs or until E goes high, whichever

occurs first. In the disabled mode, ECON is pulled

up to VOUT.

VBAT (Back-up Battery Input). When VCC falls

below VSO, VOUT switches from VCC to VBAT.

When VCC rises above VSO + hysteresis, VOUT re-

connects to VCC. VBAT may exceed VCC. Connect

to VCC if no battery is used.

Table 3. Pin Description

Pin

STM795

STM690

STM802

STM704

STM806

–

–

6

–

6

–

7

7

7

–

–

–

–

4

4

–

5

5

1

1

1

2

2

2

3

–

–

4

3

3

5

–

–

6

–

–

8

8

8

STM804

STM805

–

6

–

7

4

5

1

2

–

3

–

–

8

Name

Function

MR Push-button Reset Input

WDI Watchdog Input

RST Active-Low Reset Output

RST Active-High Reset Output

PFI Power-fail Input

PFO Power-fail Output

VOUT Supply Output for External LPSRAM

VCC Supply Voltage

Vccsw VCC Switch Output

VSS Ground

E Chip Enable Input

ECON Conditioned Chip Enable Output

VBAT Backup-Battery Input

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