
LM2576
http://onsemi.com
8
Figure 15. Typical Test Circuit
D1
MBR360
L1
100
mH
Output
2
4
Feedback
Cout
1000
mF
Cin
100
mF
LM2576
Fixed Output
1
5
3ON/OFF
GN
D
Vin
Load
Vout
D1
MBR360
L1
100
mH
Output
2
4
Feedback
Cout
1000
mF
Cin
100
mF
LM2576
Adjustable
1
5
3ON/OFF
GN
D
Vin
Load
Vout
5,000 V
Fixed Output Voltage Versions
Adjustable Output Voltage Versions
Vout + Vref 1.0 )
R2
R1
R2
+ R1
Vout
V
ref
– 1.0
Where Vref = 1.23 V, R1
between 1.0 k and 5.0 k
R2
R1
Cin
100
mF, 75 V, Aluminium Electrolytic
Cout
1000
mF, 25 V, Aluminium Electrolytic
D1
Schottky, MBR360
L1
100
mH, Pulse Eng. PE92108
R1
2.0 k, 0.1%
R2
6.12 k, 0.1%
7.0 V 40 V
Unregulated
DC Input
7.0 V 40 V
Unregulated
DC Input
PCB LAYOUT GUIDELINES
As in any switching regulator, the layout of the printed
circuit board is very important. Rapidly switching currents
associated with wiring inductance, stray capacitance and
parasitic inductance of the printed circuit board traces can
generate
voltage
transients
which
can
generate
electromagnetic interferences (EMI) and affect the desired
operation. As indicated in the Figure
15, to minimize
inductance and ground loops, the length of the leads
indicated by heavy lines should be kept as short as possible.
For best results, singlepoint grounding (as indicated) or
ground plane construction should be used.
On the other hand, the PCB area connected to the Pin 2
(emitter of the internal switch) of the LM2576 should be
kept to a minimum in order to minimize coupling to sensitive
circuitry.
Another sensitive part of the circuit is the feedback. It is
important to keep the sensitive feedback wiring short. To
assure this, physically locate the programming resistors near
to the regulator, when using the adjustable version of the
LM2576 regulator.