Datasheet
OUT IN(max) FD
MIN
OUT FD
V V V
24 V 14 V 0.5 V
D 42.9%
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(max)
RIPPLE(max)
MIN
I
2
I 0.3 0.3 1.05 A
1 D 1 0.429
= ´ = ´ =
- -
IN(max)
MIN MIN
RIPPLE(max) SW
V
1 14 V 1
L D 0.429 9.5 H
I 1.05 A 600kHz
» ´ ´ = ´ ´ = m
f
IN
RIPPLE(V typ)
SW
V
1 12V 1
I D 0.50 1.02 A
L 10 H 600kHz
» ´ ´ = ´ ´ =
mf
in
IN
RIPPLE(Vinmin)
SW
V
1 8 V 1
I D 0.673 0.90 A
L 10 H 600kHz
» ´ ´ = ´ ´ =
mf
( )
(
)
( )
( )
( )
( )
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 0.90A 6.13 Arms
1 D 1 0.673
æ ö
æ ö
= + » + = + ´ =
ç ÷
ç ÷
ç ÷
- -
è ø
è ø
( ) ( )
OUT(max)
1 1
Lpeak RIPPLE(Vinmin)
2 2
MAX
I
2
I I 0.90 6.57 A
1 D 1 0.673
» + = + =
- -
TPS40210, TPS40211
www.ti.com
SLUS772E –MARCH 2008– REVISED OCTOBER 2011
Table 2. TPS40210 Design Example Specifications (continued)
PARAMETER CONDITIONS MIN NOM MAX UNIT
SYSTEM CHARACTERISTICS
f
SW
Switching frequency 600 kHz
η
PK
Peak efficiency V
IN
= 12 V 95%
η Full load efficiency V
IN
= 12 V, I
OUT
= 2 A 94%
T
OP
Operating temperature range 8 V ≤ V
IN
≤ 14 V, 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 an estimated forward drop (V
FD
) of 0.5 V for a schottky rectifier diode, the approximate duty cycle is 42.9%
(minimum) to 67.3% (maximum).
Inductor Selection
The peak-to-peak ripple is chosen to be 30% of the maximum input current.
(34)
The minimum inductor size can be estimated using Equation 35.
(35)
The next higher standard inductor value of 10 μH is selected. The ripple current for nominal and minimum V
IN
is
estimated by Equation 36 and Equation 37.
(36)
(37)
The worst case peak-to-peak ripple current occurs at 50% duty cycle (V
IN
= 12.25 V) 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.
(39)
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