Datasheet

STM6904 Operation
Doc ID 14289 Rev 3 9/20
3 Operation
The STM6904 provides the ability to monitor critical voltages such as power-supply and
battery voltage levels, while interfacing easily to the system controllers/microprocessors.
Figure 4 shows typical hardware hookup for monitoring four voltages; two fixed thresholds
(customer-selectable, factory-programmed) and two adjustable monitor inputs. RST
output
is open drain and requires a 10 kΩ pull-up resistor tied to V
CC
.
3.1 Setting the adjustable voltage levels for V3IN and V4IN inputs
The user can customize the minimum voltage levels for the two adjustable voltage inputs by
connecting an external resistor divider network to the V3IN and V4IN pins in order to set the
trip point at some voltage above the 600 mv (V
REF
) according to the following formula:
During normal operation, the STM6904 monitors the voltage levels at all four pins (V
CC
,
V2IN, V3IN, and V4IN).
3.2 Power on reset (t
REC
)
On power up, the STM6904 activates a power on reset circuit which asserts the reset pin
(i.e. RST
goes low). The RST signal remains active until V
CC
(and V2IN, V3IN, V4IN and
MR)
rises above the minimum voltage level for the time period t
REC
thereby ensuring that
the supply voltage has stabilized to sufficient operating levels.
V
TRIP
0.6V
R1 R2+
R2
----------------------
×=