Datasheet

OUT IN(max) FD
MIN
OUT FD
V V V
24 V 14 V 0.5 V
D 42.8%
V V 24 V 0.5 V
- +
- +
» = =
+ +
OUT IN(min) FD
MAX
OUT FD
V V V
24 V 8 V 0.5 V
D 67.3%
V V 24 V 0.5 V
- +
- +
» = =
+ +
OUT(m ax)
Lrip(m ax)
MIN
I
2
I 0.3 0.3 1.05 A
1 D 1 0.428
= ´ = ´ =
- -
IN(max)
MIN MIN
Lrip(max) SW
V
1 14 V 1
L » D 0.428 9.5 H
I f 1.05 A 600kHz
´ ´ = ´ ´ = m
f
IN
RIPPLE
SW
V
1 12 V 1
I D 0.50 1.02 A
L 10 H 600 kHz
» ´ ´ = ´ ´ =
m
f
IN
RIPPLE(Vinmin)
SW
V
1 8 V 1
I D 0.673 0.89 A
L 10 H 600kHz
» ´ ´ = ´ ´ =
m
( )
(
)
( )
( )
( )
( )
2
2
2
2
2
2
OUT(max)
1 1 1
Lrms RIPPLE RIPPLE(VINmin)
L avg
12 12 12
MAX
I
2
I I I I 0.817A 6.13 Arms
1 D 1 0.673
æ ö
æ ö
= + » + = + ´ =
ç ÷
ç ÷
ç ÷
- -
è ø
è ø
TPS40210-Q1, TPS40211-Q1
www.ti.com SLVS861D –AUGUST 2008–REVISED APRIL 2010
Table 1. TPS40210 Design Example Specifications (continued)
PARAMETER CONDITIONS MIN NOM MAX UNIT
SYSTEM CHARACTERISTICS
f
SW
Switching frequency 600 kHz
h
PK
Peak efficiency V
IN
= 12 V, 0.2 A ≤ I
OUT
≤ 2 A 95%
h Full load efficiency V
IN
= 12 V, I
OUT
= 2 A 94%
T
OP
Operating temperature range 10 V ≤ V
IN
≤ 14 V, 0.2 A ≤ I
OUT
≤ 2 A 25 °C
MECHANICAL DIMENSIONS
W Width 1.5
L Length 1.5 in
h Height 0.5
Step-By-Step Design Procedure
Duty Cycle Estimation
The duty cycle of the main switching MOSFET is estimated using Equation 32 and Equation 33.
(32)
(33)
Using and estimated forward drop of 0.5 V for a Schottky rectifier diode, the approximate duty cycle is 42.8%
(minimum) to 67.3% (maximum).
Inductor Selection
The peak-to-peak ripple is limited to 30% of the maximum output current.
(34)
The minimum inductor size can be estimated using Equation 35.
(35)
The next higher standard inductor value of 10 mH is selected. The ripple current is estimated by Equation 36.
(36)
(37)
The worst-case peak-to-peak ripple current occurs at 50% duty cycle and is estimated as 1.02 A. Worst-case
RMS current through the inductor is approximated by Equation 38.
(38)
The worst case RMS inductor current is 6.13 Arms. The peak inductor current is estimated by Equation 39.
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