
LM2599 Series Buck Regulator Design Procedure (Fixed Output)
(Continued)
LM2599 Series Buck Regulator Design Procedure (Adjustable Output)
PROCEDURE (Adjustable Output Voltage Version)
EXAMPLE (Adjustable Output Voltage Version)
Given:
V
OUT
= Regulated Output Voltage
V
IN
(max) = Maximum Input Voltage
I
LOAD
(max) = Maximum Load Current
F = Switching Frequency (Fixed at a nominal 150 kHz).
Given:
V
OUT
= 20V
V
IN
(max) = 28V
I
LOAD
(max) = 3A
F = Switching Frequency (Fixed at a nominal 150 kHz).
1. Programming Output Voltage
(Selecting R
1
and R
2
, as
shown in Figure 1)
Use the following formula to select the appropriate resistor
values.
Select a value for R
between 240
and 1.5 k
. The lower
resistor values minimize noise pickup in the sensitive feed-
back pin. (For the lowest temperature coefficient and the best
stability with time, use 1% metal film resistors.)
1. Programming Output Voltage
(Selecting R
1
and R
2
, as
shown in Figure 1)
Select R
1
to be 1 k
, 1%. Solve for R
2
.
R
2
= 1k (16.26 1) = 15.26k, closest 1% value is 15.4 k
.
R
2
= 15.4 k
.
Conditions
Inductor
Output Capacitor
Through Hole Electrolytic
Panasonic
HFQ Series
(μF/V)
470/25
560/35
680/35
560/35
470/25
330/35
330/35
470/25
560/25
330/35
330/35
470/25
180/35
180/35
470/25
330/25
180/25
180/35
330/25
180/25
82/25
Surface Mount Tantalum
AVX TPS
Series
(μF/V)
330/6.3
330/6.3
330/6.3
330/6.3
330/6.3
330/6.3
220/10
220/10
220/10
220/10
220/10
220/10
100/10
100/10
100/16
100/16
100/16
100/16
100/16
100/16
68/20
Output
Voltage
(V)
Load
Current
(A)
Max Input
Voltage
(V)
5
7
10
40
6
10
40
8
10
15
40
9
20
40
15
18
30
40
15
20
40
Inductance
(μH)
Inductor
(
#
)
Nichicon
PL Series
(μF/V)
560/16
560/35
680/35
470/35
470/35
330/35
270/50
560/16
560/25
330/35
270/35
560/16
180/35
180/35
470/25
330/25
180/25
180/35
330/25
180/25
82/25
Sprague
595D Series
(μF/V)
390/6.3
390/6.3
390/6.3
390/6.3
390/6.3
390/6.3
330/10
330/10
330/10
330/10
330/10
330/10
270/10
270/10
180/16
180/16
120/20
120/20
180/16
120/20
68/25
3.3
3
22
22
22
33
22
33
47
22
22
33
47
22
68
68
22
33
68
68
33
68
150
L41
L41
L41
L40
L33
L32
L39
L41
L41
L40
L39
L33
L38
L38
L41
L40
L44
L44
L32
L38
L42
2
5
3
2
12
3
2
FIGURE 2. LM2599 Fixed Voltage Quick Design Component Selection Table
L
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