Datasheet

( )
´
´
< ´ D = ´ =
´
2
TRAN
TRAN TRAN TRAN
OVER
OUT OUT OUT OUT OUT
I L
I I I L
V T
C C V V C
( ) ( )
(
)
( )
( )
( ) ( ) ( )
= + ´ = + ´ = + ´ =
2
2
2 2 2 2
1 1 1
RIPPLE OUT RIPPLE
L rms L avg
12 12 12
I I I I I 6 1.86 6.02 A
( )
( )
-
-
» ´ ´ = ´ ´ = m
´ ´
OUT
IN max
OUT
OUT SW
IN max
V V
V
1 60 V 5 V 5 V 1
L 8.5 H
0.3 I V f 0.3 6 A 60 V 300kHz
TPS40170
www.ti.com SLUS970A –MARCH 2011–REVISED NOVEMBER 2013
DESIGN EXAMPLE
Introduction
The wide input TPS40170 controller can function in a very wide range of applications. This example describes
the design process for a very wide input (10 V to 60 V) to regulated 5-V output at a load current of 6 A. The
schematic shown in Figure 38 is configured for the design parameters provided in Table 1.
Table 1. Design Example Parameters
PARAMETER TEST CONDITIONS MIN NOM MAX UNIT
V
IN
Input voltage 10 60 V
V
IN(ripple)
Input ripple I
OUT
= 6 A 0.5 V
V
OUT
Output voltage 0 A ≤ I
OUT
≤ 20 A 4.8 5.0 5.2 V
Line regulation 10 V ≤ V
IN
≤ 60 V 0.5%
Load regulation 0 A ≤ I
OUT
≤ 6 A 0.5%
V
RIPPLE
Output ripple I
OUT
= 6 A 100 mV
V
OVER
Output overshoot ΔI
OUT
= 2.5 A 250 mV
V
UNDER
Output undershoot ΔI
OUT
= -2.5 A 250 mV
I
OUT
Output current 10 V ≤ V
IN
≤ 60 V 0 6 A
t
SS
Soft-start time V
IN
= 24 V 4 ms
I
SCP
Short circuit current trip point 8 A
η Efficiency V
IN
= 24 V, I
OUT
= 6 A 94%
f
SW
Switching frequency 300 kHz
Size 1.5 in
2
Design Procedure
Select A Switching Frequency
To maintain acceptable efficiency and meet minimum on-time requirements, a 300 kHz switching frequency is
selected.
Inductor Selection (L1).
Synchronous buck power inductors are typically sized for approximately 20-40% peak-to-peak ripple current
(I
RIPPLE
) Given this target ripple current, the required inductor size can be calculated in Equation 19.
(19)
Selecting a standard 8.2 µH inductor value, solving for I
RIPPLE
=1.86 A.
The RMS current through the inductor is approximated by Equation 20.
(20)
Output Capacitor Selection (C9)
The selection of the output capacitor is typically driven by the output transient response. The Equation 21 and
Equation 22 overestimate the voltage deviation to account for delays in the loop bandwidth and can be used to
determine the required output capacitance:
(21)
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