MCP102-195ESLASHTO datasheet(13/28 Pages) MICROCHIP

13 / 28 page

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DS20001906D-page 13

MCP102/103/121/131

4.0

APPLICATION INFORMATION

For many of today’s microcontroller applications, care

must be taken to prevent low-power conditions that can

cause many different system problems. The most

common causes are brown-out conditions, where the

system supply drops below the operating level

momentarily. The second most common cause is when

slowly

decaying

power

supply

causes

the

microcontroller to begin executing instructions without

sufficient voltage to sustain volatile memory (RAM),

thus producing indeterminate results. Figure 4-1 shows

a typical application circuit.

MCP102/103/121/131 are voltage supervisor devices

designed to keep a microcontroller in reset until the

system voltage has reached and stabilized at the

proper level for reliable system operation. These

devices also operate as protection from brown-out

conditions.

FIGURE 4-1:

Typical Application Circuit.

4.1

RST Operation

The RST output pin operation determines how the

device can be used and indicates when the system

should be forced into reset. To accomplish this, an

internal voltage reference is used to set the voltage trip

point (VTRIP). Additionally, there is a hysteresis on this

trip point.

When the falling edge of VDD crosses this voltage

threshold, the reset power-down timer (tRPD) starts.

When this delay timer times out, the RST pin is forced

low.

When the rising edge of VDD crosses this voltage

threshold, the reset power-up timer (tRPU) starts. When

this delay timer times out, the RST pin is forced high,

tRPU is active and there is additional system current.

The actual voltage trip point (VTRIPAC) will be between

the minimum trip point (VTRIPMIN) and the maximum

trip point (VTRIPMAX). The hysteresis on this trip point

and the delay timer (tRPU) are to remove any “jitter” that

would occur on the RST pin when the device VDD is at

the trip point.

Figure 4-2 shows the waveform of the RST pin as

determined by the VDD voltage, while Table 4-1 shows

the state of the RST pin. The VTRIP specification is for

falling VDD voltages. When the VDD voltage is rising, the

RST will not be driven high until VDD is at VTRIP +VHYS.

Once VDD has crossed the voltage trip point, there is

also a minimal delay time (tRPD) before the RST pin is

driven low.

FIGURE 4-2:

RST

Operation as Determined by the VTRIP and VHYS.

VDD

MCLR

(Reset input)

(Active-low)

VSS

PIC®

Microcontroller

RPU

Note 1: Resistor RPU may be required with the

MCP121 due to the open-drain output.

Resistor RPU may not be required with

the MCP131 due to the internal pull-up

resistor. The MCP102 and MCP103 do

not require the external pull-up resistor.

0.1

µF

MCP1XX

VDD

RST

VSS

TABLE 4-1:

RST PIN STATES

Device

State of RST Pin when:

Output

Driver

VDD <VTRIP

VDD >

VTRIP + VHYS

MCP102

Push-pull

MCP103

Push-pull

MCP121

LH (1)

Open-drain (1)

MCP131

LH (2)

Open-drain (2)

Note 1: Requires external pull-up resistor

2: Has internal pull-up resistor

VDD

VTRIPMAX

VTRIPMIN

VTRIPAC

VTRIPAC +VHYSAC

RST

< 1V is outside the

device specifications

tRPD

tRPU

tRPD

tRPU

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