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L4949D View Datasheet(PDF) - ON Semiconductor

Part Name
Description
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L4949D Datasheet PDF : 10 Pages
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L4949, NCV4949
Reset Circuit
The block circuit diagram of the reset circuit is shown in
Figure 16.
The reset circuit supervises the output voltage. The reset
threshold of 4.5 V is defined with the internal reference
voltage and standby output divider.
The reset pulse delay time tRD, is defined with the charge
time of an external capacitor CT:
tRD
+
CT x
2.0
2.0
mA
V
The reaction time of the reset circuit originates from the
discharge time limitation of the reset capacitor CT and is
proportional to the value of CT. The reaction time of the reset
circuit increases the noise immunity.
1.23 V Vref
22 k
2.0 mA
Reset
Out
Reg
CT
+
2.0 V
Figure 16. Reset Circuit
Standby output voltage drops below the reset threshold
only a bit longer than the reaction time results in a shorter
reset delay time.
The nominal reset delay time will be generated for
standby output voltage drops longer than approximately
50 ms. The typical reset output waveforms are shown in
Figure 17.
Vout
Vin
40 V
5.0 V
Vout1
VRT + 0.1 V
UKT
3.0 V
t
tR
Reset
tRD
tRD
tRR
Switch On
Input Drop Dump
Output
Overload
Switch Off
Figure 17. Typical Reset Output Waveforms
Sense Comparator
The sense comparator compares an input signal with an
internal voltage reference of typical 1.23 V. The use of an
external voltage divider makes this comparator very flexible
in the application.
It can be used to supervise the input voltage either before
or after the protection diode and to give additional
information to the microprocessor like low voltage warnings.
ORDERING INFORMATION
Device
Operating Temperature Range
Package
Shipping
L4949N
PDIP−8
50 Units / Rail
L4949NG
PDIP−8
(Pb−Free)
50 Units / Rail
L4949D
SOIC−8
98 Units / Rail
L4949DG
SOIC−8
(Pb−Free)
98 Units / Rail
L4949DR2
SOIC−8
2500 Units / Tape & Reel
L4949DR2G
NCV4949DG*
TJ = −40°C to +125°C
SOIC−8
(Pb−Free)
SOIC−8
(Pb−Free)
2500 Units / Tape & Reel
98 Units / Rail
NCV4949DR2*
SOIC−8
2500 Units / Tape & Reel
NCV4949DR2G*
SOIC−8
(Pb−Free)
2500 Units / Tape & Reel
NCV4949DWR2*
SOIC−20W
1000 Units / Tape & Reel
NCV4949DWR2G*
SOIC−20W
(Pb−Free)
1000 Units / Tape & Reel
†For information on tape and reel specifications,including part orientation and tape sizes, please refer to our Tape and Reel Packaging
Specifications Brochure, BRD8011/D.
*NCV4949: Tlow = −40°C, Thigh = +125°C. Guaranteed by design.
NCV prefix is for automotive and other applications requiring site and change control.
http://onsemi.com
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