MIC2788 MICREL [Micrel Semiconductor], MIC2788 Datasheet - Page 10

• Manufacturer Part Number: MIC2788
• Description: Push-Button Reset IC
• Manufacturer: MICREL [Micrel Semiconductor]

Micrel, Inc.
Application Information
Design and Product Advantages
The dual reset programmability of the MIC2788/
MIC2789 allows for already existing manual push
buttons to be used to generate a hardware reset based
on pre-programmed timing requirements. This ability to
increase the functionality of already existing buttons,
allows for cost reduction and more robust phone
designs. The dual reset delay time allows for significant
protection against accidental resets due to its long time
duration and dual push button requirement. The fixed
reset timeout delay allows for more predictable phone
operation during hardware resets. The tri-state option
provides an easy to use way to select between three
reset delay time options with no additional external
components required.
Supply Bypass Capacitor
A 0.1µF input bypass capacitor must be placed from V
(Pin 8) to GND (Pin 2).
Programmable Delay Pin (PDY)
The MIC2788/MIC2789 has a programmable dual reset
delay time, t
configuration. The PDY pin is intended to be connected
to the V
Dual Manual Reset Inputs (/MR0, /MR1)
The /MR0, /MR1 input pins have integrated pull-up
resistors for the MIC2788 but require external pull-up
resistors for the MIC2789. A recommended value is
100kΩ to keep the current consumption low when the
push-button switches are pressed. The behavior of the
reset outputs is independent of the order in which the
/MR0, /MR1 inputs are driven low. If both inputs are low
for a setup delay time, only one reset pulse, of width
t
longer time does not generate additional reset output
pulses.
Reset Outputs (/RST and RSTP)
The /RST output is a simple open-drain N-channel
MOSFET structure that requires a pull-up resistor. For
most applications, the pull-up voltage will be the same
as the power supply that supplies V
MIC2788/MIC2789. As shown in Figure 1, it is possible
October 2011
RESET
PDY Configuration
, is generated.
IN
supply voltage, ground or left floating.
OPEN
GND
V
IN
SETUP
, that is set via a tri-state logic
Keeping both inputs low for a
t
SETUP
2s
4s
6s
IN
to the
IN
10
to tie this resistor to some other voltage, other than V
thus enabling level-shifting of the /RST output. The pull-
up voltage must be limited to 5.5V or less to avoid
damage to the MIC2788/MIC2789. The pull-up resistor
must be small enough to supply current to the inputs and
leakage paths that are driven by the /RST output. A
recommended value is 100kΩ. Leave floating if the /RST
pin is unused.
The RSTP pin is a push-pull output that is driven to V
It cannot be level-shifted to another voltage. It is an
inverted signal of /RST.
The reset outputs /RST and RSTP are asserted when
the dual reset delay time, t
/MR0, /MR1 pins are driven low. Both the reset outputs
remain asserted for a factory-programmed reset timeout
delay time t
or 240ms minimum t
driven active low while the RSTP pin is driven active
high for the t
asserted for V
Figure 1. MIC2788/MIC2789 Used in Multiple Supply
RESET
Figure 2. Manual Reset Function
RESET
IN
< 1.6V.
. Two options are available with 140ms
duration. The reset outputs are de-
RESET
System
SETUP
duration. The /RST pin is
, is exceeded while the
MIC2788/MIC2789
M9999-102711-A
IN
IN
,
.