MIC2774 Micrel Semiconductor, MIC2774 Datasheet - Page 5

• Manufacturer Part Number: MIC2774
• Description: Dual Micro-Power Low Voltage Supervisor Advance Information
• Manufacturer: Micrel Semiconductor

Functional Diagram
Functional Description
IN, Under-Voltage Detector Input
The voltage present at the IN pin is compared to the internal
300mV reference voltage. A reset is triggered if and when V
falls below V
the input voltage to be monitored such that V
V
trip-point. Hysteresis is employed to prevent chattering due to
noise. The comparator on the IN pin is relatively immune to
very brief negative-going transients.
V
The V
tored input voltage. The voltage at this pin is continually
compared against the internal reference. The trip-point at
which a reset occurs is factory programmed. A reset is
triggered if and when V
esis is employed to prevent chattering due to noise. The
comparator on the V
negative-going transients.
RST, /RST Reset Output
Typically, the MIC2774 is used to monitor the power supplies
of intelligent circuits such as microcontrollers and micropro-
cessors. By connecting the appropriate reset output of a
September 29, 2000
MIC2774
REF
DD
Input
as the voltage being monitored falls below the desired
DD
pin is both the power supply terminal and a moni-
REF
. Typically, a resistor divider is used to scale
/MR
V
IN
DD
DD
input is relatively immune to very brief
DD
V
* Pinout and polarity vary by device type.
See ordering information table.
DD
falls below the trip-point. Hyster-
I
PU
GND
V
V
REF
REF
IN
will fall below
IN
5
MIC2774 to the reset input of a µC or µP, the processor will
be properly reset at power-on and during power-down and
brown-out conditions. In addition, asserting /MR, the manual
reset input, will activate the reset function.
The reset output is asserted any time /MR is asserted or if V
or V
reset output remains asserted for t
V
and/or /MR is released. A reset pulse is also generated at
power-on. Hysteresis is included in the comparators to pre-
vent chattering of the output due to noise.
/MR, Manual Reset Input
The ability to initiate a reset via external logic or a manual
switch is provided in addition to the MIC2774’s automatic
supervisory functions. Driving the /MR input to a logic low
causes an immediate and unconditional reset to occur.
Assuming V
released (returns high), the reset output will be de-asserted
no less than t
or mechanical switch. Typically, a momentary push-button
switch is connected such that /MR is shorted to ground when
the switch contacts close. Switch de-bouncing is performed
internally; the switch may be connected directly between /MR
and GND. /MR is internally pulled-up to V
open if unused.
DD
Delay
Line
DD
subsequently return above the threshold boundaries
drops below the corresponding threshold voltage. The
One Shot
IN
RST
and V
later. /MR may be driven by a logic signal,
DD
R
S
MIC2774
are within tolerance when /MR is
/Q
Q
RST
/RST*
RST*
(min) after V
DD
and may be left
MIC2774
IN
and/or
Micrel
IN