LM2574-12 Motorola Inc, LM2574-12 Datasheet - Page 20

• Manufacturer Part Number: LM2574-12
• Description: EASY SWITCHERE 0.5 A STEP-DOWN VOLTAGE REGULATOR
• Manufacturer: Motorola Inc

Undervoltage Lockout
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
following expression:
20
Some applications require the regulator to remain off until
1N5242B
Figure 33. Undervoltage Lockout Circuit for
+V in
+V in
NOTE: This picture does not show the complete circuit.
NOTE: This picture does not show the complete circuit.
22 F
10 k
10 k
R1
Z1
R2
Figure 32. Delayed Startup Circuitry
C in
V
th
47 k
R3
[
Buck Converter
Q1
2N3904
V
Z1
C1
0.1 F
47 k
R1
)
+V in
5
C in
22 F
1.0
+V in
3
5
)
LM2574–XX
ON/OFF
R2
47 k
R2
R1
3
LM2574–XX
ON/OFF
V
and
BE
2
4
(Q1)
and
Gnds
Pins
2
4
Gnds
Pins
LM2574
Adjustable Output, Low–Ripple Power Supply
features an adjustable output voltage is shown in Figure 35.
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.
NOTE: This picture does not show the complete circuit (see Figure 27).
A 0.5 A output current capability power supply that
This regulator delivers 0.5 A into 1.2 to 35 V output. The
1N5242
+V in
15 k
15 k
Figure 34. Undervoltage Lockout Circuit for
R2
Z1
R1
68 k
R3
MOTOROLA ANALOG IC DEVICE DATA
Buck–Boost Converter
Q1
2N3904
C in
22 F
+V in
5
3
LM2574–XX
ON/OFF
and
2
4
Gnds
Pins
–V out