DocID14290 Rev 4 7/19
STM6905 Pin descriptions
18
2 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 the t
REC
after MR returns to high. The active-low input has an internal 10 kΩ pull-up
resistor to V
CC
. It can be driven from a TTL or CMOS logic line, or with open drain/collector
outputs, or connected to V
SS
through a switch. If unused, leave this pin open or connect it to
V
CC
.
Connect a normally open momentary switch from MR to V
SS
. An external debounce circuitry
is not required (if
MR is driven from long cables or if the device is used in noisy
environments, connecting a 0.1 µF capacitor from
MR to V
SS
provides additional noise
immunity).
2.2 V
CC
primary supply voltage monitoring input
The V
CC
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 V
SS
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 V
CC
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 t
REC
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 V
CC
.
A 10 kΩ pull-up resistor should be sufficient for most applications.
