LM2574DW-3.3 View Datasheet(PDF) - Motorola => Freescale
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Description
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LM2574DW-3.3 Datasheet PDF : 24 Pages
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Figure 32. Delayed Startup Circuitry
LM2574
Figure 34. Undervoltage Lockout Circuit for
Buck–Boost Converter
+Vin
Cin
22 µF
+Vin
5 LM2574–XX
C1
0.1 µF
R1
47 k
3 ON/OFF 2 Gnds
and Pins
4
R2
47 k
NOTE: This picture does not show the complete circuit.
Undervoltage Lockout
Some applications require the regulator to remain off until
the input voltage reaches a certain threshold level. Figure 33
shows an undervoltage lockout circuit applied to a buck
regulator. A version of this circuit for buck–boost converter is
shown in Figure 34. Resistor R3 pulls the ON/OFF pin high
and keeps the regulator off until the input voltage reaches a
predetermined threshold level, which is determined by the
[ ) ǒ ) Ǔ following expression:
Vth VZ1
1.0
R2
R1
VBE(Q1)
+Vin
R2
15 k
Z1
1N5242
R1
15 k
+Vin
LM2574–XX
5
R3
Cin
68 k
22 µF 3 ON/OFF 2 Gnds
and Pins
4
Q1
2N3904
–Vout
NOTE: This picture does not show the complete circuit (see Figure 27).
Adjustable Output, Low–Ripple Power Supply
A 0.5 A output current capability power supply that
features an adjustable output voltage is shown in Figure 35.
This regulator delivers 0.5 A into 1.2 to 35 V output. The
input voltage ranges from roughly 3.0 to 40 V. In order to
achieve a 10 or more times reduction of output ripple, an
additional L–C filter is included in this circuit.
Figure 33. Undervoltage Lockout Circuit for
Buck Converter
+Vin
R1
10 k
Z1
1N5242B
R2
10 k
+Vin
LM2574–XX
5
R3
Cin
47 k
22 µF 3 ON/OFF 2 Gnds
and Pins
4
Q1
2N3904
NOTE: This picture does not show the complete circuit.
20
MOTOROLA ANALOG IC DEVICE DATA
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