HT7082A-2 데이터 시트보기 (PDF) - Holtek Semiconductor

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HT7082A-2

TinyPower™ Voltage Detector

Holtek Semiconductor 

HT70xxA-2

Functional Description

The HT70xxA-2 series is a set of voltage detectors

equipped with a high stability voltage reference which is

connected to the negative input of a comparator¾

denoted as VREF in the following figure for NMOS output

voltage detector.

When the voltage drop to the positive input of the

comparator (i,e,VB) is higher than VREF, VOUT goes

high, M1 turns off, and VB is expressed as VBH=VDD ´

(RB+RC) / (RA+RB+RC). If VDD is decreased so that VB

falls to a value less than VREF, the comparator output

inverts from high to low, VOUT goes low, VC is high, M1

turns on, RC is bypassed, and VB becomes: VBL= VDD ´

RB / (RA+RB), which is less than VBH. By so doing, the

comparator output will stay low to prevent the circuit

from oscillating when VB » VREF.

If VDD falls below the minimum operating voltage, the

output becomes undefined. When VDD goes from low to

VDD ´ RB / (RA+RB) > VREF, the comparator output and

VOUT goes high.

The detectable voltage is defined as:

VDET

(-)

=

RA + RB + RC

RB + RC

´

VREF

The release voltage is defined as:

VDET

(+)

=

RA + RB

RB

´

VREF

The hysteresis width is:

VHYS = VDET (+) - VDET (-)

V DD

RA

C o m p a ra to r

RL

VC

VB

V OUT

V REF

RB

MN

M1

RC

V SS

NMOS Output Voltage Detector

The figure demonstrates the NMOS output type with

positive output polarity (VOUT is normally open, active

low). The HT70xxA-2 series also supplies options for

other output types with active high outputs. Application

circuits shown are examples of positive output polarity

(normally open, active low) unless otherwise specified.

Rev. 1.20

6

December 14, 2012

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