LM2575D2T-12 ON Semiconductor, LM2575D2T-12 Datasheet - Page 20

• Manufacturer Part Number: LM2575D2T-12
• Description: EASY SWITCHERE 1.0 A STEP-DOWN VOLTAGE REGULATOR
• Manufacturer: ON Semiconductor

Design Recommendations:
buck–boost converter can be applied. The output capacitor
C out must be chosen larger than would be required for a
standard buck converter. Low input voltages or high output
currents require a large value output capacitor (in the range
of thousands of F). The recommended range of inductor
values for the negative boost regulator is the same as for
inverting converter design.
converters cannot provide current limiting load protection in
the event of a short in the output so some other means, such
as a fuse, may be necessary to provide the load protection.
Delayed Startup
already mentioned above, which require a higher amount of
startup current. In such cases, if the input power source is
limited, this delayed startup feature becomes very useful.
is applied and the time when the output voltage comes up,
the circuit in Figure 30 can be used. As the input voltage is
applied, the capacitor C1 charges up, and the voltage across
the resistor R2 falls down. When the voltage on the ON/OFF
pin falls below the threshold value 1.4 V, the regulator starts
up. Resistor R1 is included to limit the maximum voltage
applied to the ON/OFF pin, reduces the power supply noise
sensitivity, and also limits the capacitor C1 discharge current,
but its use is not mandatory.
respectively) ripple voltage exists, a long delay time can
cause some problems by coupling the ripple into the ON/OFF
pin, the regulator could be switched periodically on and off
with the line (or double) frequency.
Undervoltage Lockout
the input voltage reaches a certain threshold level. Figure 31
shows an undervoltage lockout circuit applied to a buck
regulator. A version of this circuit for buck–boost converter is
20
The same design rules as for the previous inverting
Another important point is that these negative boost
There are some applications, like the inverting regulator
To provide a time delay between the time the input voltage
When a high 50 Hz or 60 Hz (100 Hz or 120 Hz
Some applications require the regulator to remain off until
100 F
+V in
NOTE:
C in
Figure 30. Delayed Startup Circuitry
This picture does not show the complete circuit.
C1
0.1 F
47 k
R1
+V in
1
5
LM2575–XX
ON/OFF
R2
47 k
3
Gnd
LM2575
shown in Figure 32. 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:
Adjustable Output, Low–Ripple Power Supply
features an adjustable output voltage is shown in Figure 33.
input voltage ranges from roughly 8.0 V 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.
1N5242B
A 1.0 A output current capability power supply that
This regulator delivers 1.0 A into 1.2 V to 35 V output. The
1N5242B
+V in
Figure 32. Undervoltage Lockout Circuit for
Figure 31. Undervoltage Lockout Circuit for
15 k
15 k
R2
Z1
R1
+V in
NOTE:
NOTE:
V
10 k
10 k
R2
Z1
R1
th
[
68 k
R3
This picture does not show the complete circuit.
V
This picture does not show the complete circuit.
47 k
MOTOROLA ANALOG IC DEVICE DATA
Buck–Boost Converter
Z1
R3
Q1
2N3904
)
Buck Converter
Q1
2N3904
1
)
C in
100 F
+V in
R2
R1
C in
100 F
1
+V in
1
V
5
BE
LM2575–5.0
5
ON/OFF
LM2575–5.0
V th 13 V
(Q1)
ON/OFF
3
3
Gnd
V out = –5.0 V
V th 13 V
Gnd