TC4949 查看數據表（PDF） - TelCom Semiconductor Inc => Microchip
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TC4949 Datasheet PDF : 9 Pages
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Multifunction Very Low Dropout Voltage Regulator
TC4949
Reset Circuit
The block circuit diagram of the reset circuit is shown in
Figure 15.
The reset circuit supervises the output voltage. The
reset thereshold of 4.5V is defined with the internal refer-
ence 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 2.0V
2.0µA
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.
1.23V VREF
22k
Out
+
–
Reg
2.0µA
+
CT –
+
- 2.0V
Reset
Figure 15. 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
50µsec. The typical reset output waveforms are shown in
Figure 16.
VOUT
VIN
40V
5.0V
VRT + 0.1V
UKT
VOUT1
3.0V
T
TR
Reset
TRD
TRR
TRD
Switch On Input Drop Dump Output Switch Off
Overload
Figure 16. Typical Reset Output Waveforms
Sense Comparator
The sense comparator compares an input signal with an
internal voltage reference of typical 1.23V. 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.
TC4949-1 1/6/00
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