Datasheet

( )
( )
OUT
IN max
OUT
OUT
OUT SW
IN max
V V
V
1 14 1.2 1
L 610nH
0.3 I V f 0.3 20 300kHz
-
-
= ´ ´ = ´ =
´ ´
TPS40400
www.ti.com SLUS930B –APRIL 2011– REVISED OCTOBER 2011
DESIGN EXAMPLES
Design Example 1: 12-V Input, 1.2-V Output, 20-A (max) Output Current
Design Parameters
The following example illustrates the design process and component selection for a synchronous buck converter
using the TPS40400 controller. The design goal parameters are listed in Table 3.
Table 3. Design Electrical Parameters
PARAMETER NOTES AND CONDITIONS MIN NOM MAX UNITS
INPUT CHARACTERISTICS
V
IN
Input voltage 8 12 14 V
I
IN
Input current V
IN
= 8 V, I
OUT
= 20 A 3.6 A
No load input current V
IN
= 12 V, I
OUT
= 0 A 60 mA
V
IN(start)
V
IN
start voltage 7 V
V
IN(stop)
V
IN
stop voltage 5 V
OUTPUT CHARACTERISTICS
V
OUT
Output voltage V
IN
= 12 V, I
OUT
= 20 A 1.08 1.2 1.32 V
Line regulation 8 ≤ V
IN
≤ 14 V, I
OUT
= 20 A 0.5%
Load regulation V
IN
= 12 V, 0 A ≤ I
OUT
≤ 20 A 0.5%
Vout_ripple Output ripple voltage V
IN
= 12 V, I
OUT
= 20 A 50 mV
P-P
Iout Output current 8 ≤ V
IN
≤ 14 0 20 A
I
OCP
Output over current inception point V
IN
= 12 V 21 25 29 A
SS Soft-start time (default) 2.8 ms
Transient response
ΔI Load step 10 A ≤ I
OUT
≤ 20 A 10 A
Load slew rate 1 A/μS
Overshoot 120 mV
Settling time 20 μs
SYSTEM CHARACTERISTICS
f
SW
Switching frequency 300 kHz
η
PK
Peak efficiency V
IN
= 12 V, 0 A ≤ I
OUT
≤ 20 A 90%
η Full load efficiency V
IN
= 12 V, I
OUT
= 20 A 85%
T
OPER
Operating temperature range 8 ≤ V
IN
≤ 14 V, 0 A ≤ I
OUT
≤ 20 A –40 60 °C
Design Procedure
The following design example is for an output of 1.2 V at 20-A maximum, with an input range of 8 V to 14 V.
Selecting a Switching Frequency
This design example is calculated for a switching frequency of 300 kHz to improve efficiency. The switching
frequency can be changed with the Fusion GUI, but some components may need to be revised at other switching
frequencies.
Output Inductor, L
OUT
The output inductor value is determined by the peak-to-peak ripple at high line, and in this case a value of 30%
of output current maximum is used.
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