HT7024A-3 Ver la hoja de datos (PDF) - Holtek Semiconductor
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HT7024A-3 Datasheet PDF : 15 Pages
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HT70xxA-3
Functional Description
The HT70xxA-3 series is a set of voltage detectors
equipped with a high stability voltage reference which
is connected to the negative input of a comparator
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-3 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. 1.00
7
April 18, 2013
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