Datasheet

f
Z
+
1
2p 0.012 180 mF
+ 74 kHz
f
LC
+
1
2p 10 mH 180 mF
Ǹ
+ 3.7 kHz
MOD(dB)
A 20 log(9) 19 dB= ´ =
MOD
18
A 9
2
= =
R
ILIM
+
10 0.14
I
SINK
)
V
OS
I
SINK
W +
10 0.14
8.3 m A
)
(
50 mV
)
8.3 mA
W + 175 kW + 174 kW
I
LIM
u
180 mF 3.3
1 m
) 7.0 + 7.6 A
C
SS
+
2.3 mA
0.7 V
1 ms + 3.28 nF + 3300 pF
33 mV + 2.0
ǒ
ESR )
1
8 180 mF 130 kHz
Ǔ
33 mV + 2.0
ǒ
ESR )
1
8 127 mF 130 kHz
Ǔ
C
O
+
10 mH
ǒ
5
2
* 1
2
Ǔ
ǒ
3.3
2
* 3.0
2
Ǔ
+ 127 mF
TPS40060
TPS40061
SLUS543F –DECEMBER 2002–REVISED JUNE 2013 www.ti.com
9. Calculating the Output Capacitance (C
O
)
In this example. the output capacitance is determined by the load response requirement of ΔV = 0.3 V for a 1 A
to 5 A step load. C
O
can be calculated using Equation 18.
(60)
Using Equation 13 calculate the ESR required to meet the output ripple requirements.
(61)
ESR = 8.9 mΩ
In order to get the required ESR, the capacitance needs to be greater than the 127-µF calculated. For example,
a single Panasonic SP capacitor, 180-µF with ESR of 12 mΩ can be used. Re-calculating the ESR required with
the new value of 180-µF is shown in Equation 62.
(62)
ESR = 11.1 mΩ
10. Calculate the Soft-Start Capacitor (C
SS
)
This design requires a soft-start time (t
START
) of 1 ms. C
SS
is calculated in Equation 63.
(63)
11. Calculate the Current Limit Resistor (R
ILIM
)
The current limit set point depends on t
START
, V
O
, C
O
and I
LOAD
at start up as shown in Equation 7.
(64)
Set I
LIM
for 10.0 A minimum, then from Equation 7
(65)
12. Calculate Loop Compensation Values
Calculate the DC modulator gain (A
MOD
) from Equation 20.
(66)
(67)
Calculate the output poles and zeros from Equation 21 and Equation 22 of the L-C filter.
(68)
and
(69)
Select the close-loop 0 dB crossover frequency, f
C
. For this example f
C
= 10 kHz.
Select the double zero location for the Type III compensation network at the output filter double pole at 3.7 kHz.
Select the double pole location for the Type III compensation network at the output capacitor ESR zero at 73.7
kHz.
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