STM6904 Pin descriptions
Doc ID 14289 Rev 3 7/20
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 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
; 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 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 to
1.050 V.
2.4 V
SS
This pin is the ground pin for the power supply.
2.5 V3IN and V4IN
The V3IN and V4IN are high impedance inputs. RST is driven low when the voltage (V
TRIP
)
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 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.
2.7 TR
SEL
input
Allows user to select between two values of t
REC
timing (210 or 420 ms). Pin must be tied to
V
SS
(210 ms) or V
CC
(420 ms).
