SC4501 查看數據表（PDF） - Semtech Corporation
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SC4501 Datasheet PDF : 21 Pages
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POWER MANAGEMENT
Application Information
IN
SC4501
SHDN
(a)
VIN
1N4148
IN
SC4501
SHDN
SC4501
IN
SC4501
SHDN
(b)
IN
SC4501
SHDN
(c)
(d)
Figure 6. Methods of Driving the Shutdown Pin
(a) Directly Driven from a Logic Gate
(b)
(c)
(d)
Driven from an Open-drain N-channel MOSFET or an Open-Collector
DCroimvebninfirnogmSahuLtodgoicwGn awteithwPitrhoVgrOaH m>mVIeNd UVLO (See Section Below).
NPN
Transistor
(VOL
<
0.1V)
Programming Undervoltage Lockout
The SC4501 has an internal VIN undervoltage lockout
(UVLO) threshold of 1.4V. The transition from idle to
switching is abrupt but there is no hysteresis. If the input
voltage ramp rate is slow and the input bypass is limited,
then sudden turn on of the power transistor will cause a
dip in the line voltage. Switching will stop if VIN falls below
the internal UVLO threshold. The resulting output voltage
rise may be non-monotonic. The 1.1V disable threshold of
the SC4501 can be used in conjunction with a resistive
voltage divider to raise the UVLO threshold and to add an
UVLO hysteresis. Figure 7 shows the scheme. Both VH and
VL (the desired upper and the lower UVLO threshold
voltages) are determined by the 1.1V threshold crossings,
VH and VL are therefore:
VH
=
1
+
R3
R4
(1.1 V )
VL = VH − VHYS = VH − IHYSR3
Re-arranging,
R3
=
VHYS
IHYS
R4
=
R3
VH
1.1
−
1
© 2005 Semtech Corp.
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