LM2576
predetermined threshold level with respect to the ground
Under normal continuous inductor current operating
Pin 3, which is determined by the following expression:
conditions, the worst case occurs when V is minimal.
in
R2
R1
( )
Q1
V
V
1.0
V
th
Z1
BE
Figure 33. Undervoltage Lockout Circuit for
Buck–Boost Converter
Figure 32. Undervoltage Lockout Circuit for
Buck Converter
+V
in
+V
in
LM2576–XX
1
+V
in
+V
in
LM2576–XX
C
100
in
R2
15 k
R3
47 k
1
5
ON/OFF
3
Gnd
µF
C
100
R2
10 k
R3
47 k
in
µF
5
ON/OFF
3
Gnd
Z1
1N5242B
V
≈ 13 V
th
Z1
1N5242B
Q1
2N3904
R1
15 k
Q1
2N3904
V
out
R1
10 k
V
≈ 13 V
th
NOTE: This picture does not show the complete circuit.
NOTE: This picture does not show the complete circuit.
Adjustable Output, Low–Ripple Power Supply
A 3.0 A output current capability power supply that
features an adjustable output voltage is shown in Figure 34.
This regulator delivers 3.0 A into 1.2 V to 35 V output. The
input voltage ranges from roughly 3.0 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.
The following formula is used to obtain the peak inductor
current:
I
(V
|V |)
V
x t
on
Load in
O
in
2L
I
peak
on
V
1
in
|V |
O
1.0
where t
x
, and f
52 kHz.
osc
V
|V |
f
osc
in
O
Figure 34. 1.2 to 35 V Adjustable 3.0 A Power Supply with Low Output Ripple
Feedback
4
40 V Max
Unregulated
DC Input
+V
in
L1
150
L2
LM2574–Adj
Output
Voltage
µ
H
20
µ
H
1
Output
2
1.2 to 35 V @ 3.0 A
C
µ
R2
50 k
in
3
Gnd
5
ON/OFF
100
F
C
D1
1N5822
out
2200
C1
100 µF
µF
R1
1.21 k
Optional Output
Ripple Filter
21
MOTOROLA ANALOG IC DEVICE DATA
MOTOROLA [ MOTOROLA ]
