MIC2786 データシートの表示（PDF） - Micrel

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MIC2786

Push-Button Reset IC with Voltage Supervisor

Micrel 

Micrel, Inc.

Application Information

Design and Product Advantages

The MIC2786/MIC2787 are voltage supervisor reset ICs

with dual manual reset inputs and long manual reset

setup delay times. The dual manual reset inputs and

long manual reset setup delay times help protect against

accidental system resets in applications such as smart

phones, personal navigation devices, MP3 players, and

set-top boxes (STB).

The MIC2786/MIC2787 assert and hold a reset when the

supply voltage decreases below the factory-programmed

threshold voltage. Reset is asserted for a fixed reset

timeout delay once the supply voltage increases above

the rising threshold voltage or when both manual reset

inputs are asserted low for longer than the setup delay

time.

The MIC2786/MIC2787 feature manual reset setup

delay times of 2s, 4s or 6s, which are selected by the tri-

state programmable delay input pin (PDY). They are

available with factory-programmed reset timeout delays

of 140ms (min.) or 240ms (min.). Both the MIC2786 and

MIC2787 feature an active-low, open-drain reset output

(/RST) and an active-high, push-pull reset output

(RSTP). This allows flexibility for interfacing with different

microprocessors, PMICs, and load-switches. The

MIC2786 features 65kΩ pull-up resistors on the /MR0

and /MR1 inputs to provide ease when connecting to

push-button inputs. The MIC2787 does not provide pull-

up resistors on the manual reset inputs and is intended

for directly interfacing to logic outputs.

Supply Bypass Capacitor

A 0.1µF input bypass capacitor must be placed from VIN

(Pin 8) to GND (Pin 2).

Programmable Delay Input (PDY)

The MIC2786/MIC2787 has a programmable setup

delay time, tSETUP that is set via a tri-state logic

configuration. The PDY pin is intended to be connected

to the VIN supply voltage, ground or left floating.

PDY Configuration

OPEN

GND

VIN

tSETUP

2s

4s

6s

MIC2786/MIC2787

Dual Manual Reset Inputs (/MR0, /MR1)

The /MR0, /MR1 input pins have integrated pull-up

resistors for the MIC2786 but require external pull-up

resistors for the MIC2787. 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

tRESET, is generated. Keeping both inputs low for a

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 to an

external voltage. For most applications, the pull-up

voltage will be the same as the power supply that

supplies VIN to the MIC2786/MIC2787. As shown in

Figure 1, it is possible to tie this resistor to some other

voltage, other than VIN, 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 MIC2786/MIC2787. 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.

Since the /RST output is open-drain, several reset

sources can be wire-ORed, in parallel, to allow resets

from multiple sources. By tying the pull-up resistor to

some other voltage, the MIC2786/MIC2787 can monitor

one voltage while level-shifting the /RST output to some

other voltage.

The RSTP pin is a push-pull output that is driven to VIN.

It cannot be level-shifted to another voltage. It is an

inverted signal of /RST.

October 2011

Figure 1. MIC2786/MIC2787 Used in Multiple Supply

System

10

M9999-102711-A

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