MIC2782 Datasheet, PDF (8/15 Pages) Micrel Semiconductor – Dual-Input Push Button Reset IC

Micrel, Inc.
Functional Description
Design and Product Advantages
The MIC2782 is a dual push-button input reset IC with
extended setup delay times. It is used for generating a
hard reset for microcontrollers, PMICs or load
disconnect switches. The dual manual reset inputs and
long setup delay times help protect against accidental
system resets. The fixed Reset Timeout period allows for
more predictable phone or Tablet operation during
hardware resets. It is used in applications such as smart
phones, tablets, personal navigation devices, MP3
players and Set-Top Boxes (STB).
General Functionality
As shown in Figure 1, if both /MR1 and /MR2 are
asserted low for longer than the Setup Period (t_SETUP),
the RESET output will be asserted (logic-level low) for a
Reset Timeout Period (t_RESET). During the Setup Period,
if either of the /MR1 or /MR2 inputs are de-asserted
high, then the Setup Period timer will be reset. To assert
the RESET output low again, both the /MR1 and /MR2
inputs will have to be asserted low together for the full
duration of the Setup period.
If both /MR1 and /MR2 are asserted low for longer than
the Debounce Time (t_DB), then the ANDOUT output will
be asserted, (logic-level low). ANDOUT will remain
asserted low as long as both the /MR1 and /MR2 inputs
are asserted low. If either the /MR1 or /MR2 are de-
asserted for longer that the Debounce Time (t_DB), then
the ANDOUT output will de-assert high.
Figure 1. Manual Reset Function
MIC2782
Keeping both manual reset inputs low for a longer time
does not generate additional RESET output pulses. De-
asserting either manual reset input during the RESET
pulse duration, will not reset the Setup Timer. After the
RESET pin has de-asserted high, both the manual reset
inputs must be held high for more than a Debounce
Time to reset the Setup Timer.
ANDOUT Debounce Time is a de-glitch time, typically
1.5ms, that senses the asserting of both manual reset
inputs low together. A de-glitch time is needed if the
manual reset inputs come from noisy push-button
sources. If either manual reset inputs are asserted (or
de-asserted) for less than a Debounce Time, the
ANDOUT output will not respond.
Dual Manual Reset Inputs (/MR1, /MR2)
The /MR1, /MR2 are active-low manual inputs that have
integrated 65kΩ pull-up resistors to the VDD power
supply. If both inputs are asserted (logic-level low) for a
Setup Period (t_SETUP), only one reset pulse, of width
t_RESET, is generated. The behavior of the RESET and
ANDOUT outputs is independent of the order in which
the /MR1, /MR2 inputs are driven low. The MIC2782
consumes only 2µA when /MR1 and /MR2 manual inputs
are de-asserted (logic-level high) together. Current
consumption is typically 120µA when both manual inputs
are asserted low together and 55µA when only one of
the manual inputs is asserted low while the other manual
input is de-asserted high.
Outputs (RESET and ANDOUT)
The RESET and ANDOUT outputs are simple open-
drain N-channel MOSFET structures that require a pull-
up resistor. For most applications, the pull-up voltage will
be the same as the power supply that supplies V_DD to
the MIC2782. As shown in Figure 2, it is possible to tie
this resistor to some other voltage, other than V_DD, thus
enabling level-shifting of the RESET or ANDOUT
outputs. The pull-up voltage must be limited to 5.5V to
avoid damaging the MIC2782. The pull-up resistor must
be small enough to supply current to the inputs and
leakage paths that are driven by the RESET or ANDOUT
outputs. A recommended value is 100kΩ.
Since the RESET and ANDOUT outputs are open-drain,
several reset sources can be wire-ORed, in parallel, to
allow resets from multiple sources.
February 21, 2014
8
Revision 2.0