MIC2786 Datasheet, PDF (11/17 Pages) Micrel Semiconductor – Push-Button Reset IC with Voltage Supervisor

Micrel, Inc.
Asserting /RST and RSTP Outputs
a) When Functioning as a Manual Reset
The reset outputs /RST and RSTP are asserted when
the setup delay time, t_SETUP, is exceeded while the /MR0,
/MR1 pins are driven low. Both the reset outputs remain
asserted for a factory-programmed reset timeout delay
time t_RESET. Two options are available with 140ms or
240ms minimum t_RESET duration. The /RST pin is driven
active low while the RSTP pin is driven active high for
the t_RESET duration. The reset outputs are undefined for
V_IN < 1.6V.
MIC2786/MIC2787
Figure 3. Voltage Monitor Function
V_IN Transients
The MIC2786/MIC2787 is relatively immune to small
negative-going V_IN glitches below the reset threshold. As
shown in Figure 4, the overdrive voltage is the difference
between the threshold voltage and the minimum point of
the V_IN glitch. Typically, an overdrive of 100mV, with
duration of 20μs or less will not cause a reset.
Figure 2. Manual Reset Function
b) When Functioning as a Voltage Monitor
The /RST pin is asserted whenever V_IN falls below the
reset threshold voltage, V_TH (V_IN < V_TH). The V_IN pin
circuitry includes hysteresis to prevent /RST or RSTP pin
chattering due to noise. The /RST pin remains asserted
for the duration of the reset timeout delay (t_RESET) after
V_IN has risen above the reset threshold voltage plus the
hysteresis. The reset function ensures a microprocessor
is properly reset and powers up in a known condition
after a power failure. /RST remains valid with V_IN as low
as 1.6V. The RSTP output is a compliment of the /RST
output.
Figure 4. V_IN Transient
October 2011
11
M9999-102711-A