LM2596 Просмотр технического описания (PDF) - Estek Electronics Co. Ltd
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LM2596 Datasheet PDF : 13 Pages
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LM2596
PROCEDURE (Fixed Output Voltage Version)
EXAMPLE (Fixed Output Voltage Version)
4. Input Capacitor (CIN)
4. Input Capacitor (CIN)
A low ESR aluminum or tantalum bypass capacitor is needed between the The important parameters for the Input capacitor are the input voltage rating and the
input pin and ground pin to prevent large volt-age transients from appearing RMS current rating. With a nominal
at the input. This capacitor should be located close to the IC
input voltage of 12V, an aluminum electrolytic capacitor with a voltage rating
using short leads. In addition, the RMS current rating of the input capacitor greater than 18V (1.5 x VIN ) would be needed. The next higher capacitor voltage
should be selected to be at least 1/2 the DC load current. The capacitor
rating is 25V.
manufacturers data sheet must be checked to assure that this current rating The RMS current rating requirement for the input capacitor in
is not exceeded. The curve shown in Figure 9 shows typical RMS current a buck regulator is approximately 1 /2 the DC load current. In this example, with a
ratings for several different aluminum electrolytic capacitor values.
3A load, a capacitor with a RMS current rating of at least 1.5A is needed. The
For an aluminum electrolytic, the capacitor voltage rating should be
curves shown in Figure 9 can be used to select an appropriate input capacitor.
approximately 1.5 times the maximum input voltage.
From the curves, locate the 35V line and note which capacitor values have RMS
The tantalum capacitor voltage rating should be 2 times the maximum
input voltage and it is recommended that they be surge current tested by
current ratings greater than 1.5A. A 680µF/35V capacitor could be used.
For a through hole design, a 680µF/35V electrolytic capacitor (Panasonic HFQ
the manufacturer.
series or Nichicon PL series or equivalent) would be adequate. other types or other
Use caution when using ceramic capacitors for input bypassing, because it manufacturers capacitors can be used provided the RMS ripple current ratings are
may cause severe ringing at the VIN pin.
adequate.
For surface mount designs, solid tantalum capacitors can be used, but caution must
be exercised with regard to the capacitor surge current rating. The TPS series
available from AVX, and the 593D series from Sprague are both surge current
tested.
LM2596 SERIES BUCK REGULATOR DESIGN PROCEDURE (FIXED OUTPUT) (Continued)
Output
Voltage
(V)
3.3
Conditions
Inductor
Load
Current
(A)
3
Max Input
Voltage (V)
5
Inductance
(H)
Inductor
(#)
22
390/6.3
Output Capacitor
Through Hole Electrolytic
Surface Mount Tantalum
Panasonic
HFQ Series
(F/V)
L41
Nichicon PL
Series (F/V)
470/25
AVX TPS
Series
(F/V)
560/16
Sprague 595D Series
(F/V)
330/6.3
7
22
L41
560/35
560/35
330/6.3
390/6.3
2
10
22
L41
390/6.3
680/35
680/35
330/6.3
40
5
3
6
33
L40
390/6.3
22
L33
390/6.3
560/35
470/25
470/35
470/35
330/6.3
330/6.3
10
2
40
33
L32
390/6.3
47
L39
330/10
330/35
330/35
330/35
270/50
330/6.3
220/10
8
12
3
22
L41
330/10
470/25
560/16
220/10
10
22
L41
560/25
560/25
220/10
330/10
15
2
40
33
L40
330/10
47
L39
330/10
330/35
330/35
330/35
270/35
220/10
220/10
9
22
L33
470/25
560/16
330/10
LM2596 SERIES BUCK REGULATOR DESIGN PROCEDURE (ADJUSTABLE OUTPUT)
220/10
PROCEDURE (Adjustable Output Voltage Version)
EXAMPLE (Adjustable Output Voltage Version)
Given:
Given:
VOUT = Regulated Output Voltage
VOUT = 20V
VIN(max) = Maximum Input Voltage
VIN(max) = 28V
ILOAD(max) = Maximum Load Current
F1.=PSrwoigtcrhaimngmFinregqOueuntcpyu(tFVixoeltdaagtea(Sneolmecintianlg1R501 aknHdzR).2, as shown in
Figure 1)
ILOAD(max) = 3A
F1=. SPwroitgcrhaimngmFinregquOeuntcpyu(tFVixoeldtaagtea(nSoemlecintianlg1R501 aknHdz)R. 2, as shown
in Figure 1)
Use the following formula to select the appropriate resistor values.
VOUT VREF (1 R 2 )
R 1 where
VREF 1.23
V
Select a value for R1 between 240 and 1.5k. The lower resistor
values minimize noise pickup in the sensitive feedback pin. (For the
lowest temperature coefficient and the best stability with time, use 1%
metal film resistors.)
Select R1 to be 1 k, 1%. Solve for R2.
R 2 R 1( VOUT 1) 1k( 20 V
VREF
1.23 V
R2=1k (16.26-1)=15.26k, closest 1% value is 15.4k
R2 = 15.4 k.
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