Datasheet

IN(max) OUT1
OUT1
OUT1 IN(max) SW
V V
V
1 15 V 1.2 V 1.2 V 1
L1 0.736 H
0.3 I V f 0.3 10 A 15 V 500kHz
-
-
» ´ ´ = ´ ´ = m
´ ´
TPS40322
www.ti.com SLUSAF8D –JUNE 2011–REVISED JANUARY 2014
TPS40322 Design Example 1
Dual-Output Configuration from 12-V Nominal to 1.2-V and 1.8-V DC-to-DC Converter Using the
TPS40322
The following example illustrates the design process and component selection for a dual output synchronous
buck converter using the TPS40322 controller. The design goal parameters are listed in Table 3.
Table 3. TPS40322 Dual Output Design Example Specification
PARAMETER TEST CONDITION MIN NOM MAX UNIT
INPUT CHARACTERSTICS
V
IN
Input voltage 8 12 15 V
V
IN(ripple)
Input ripple I
OUT1
= I
OUT2
= 10 A 0.25 V
OUTPUT 1 CHARACTERSTICS
V
OUT1
Output voltage I
OUT1(min)
≤ I
OUT1
≤ I
OUT1(max)
1.2 V
Line regulation V
IN(min)
≤ V
IN
≤ V
IN(max)
0.5%
Load regulation I
OUT1(min)
≤ I
OUT1
≤ I
OUT1(max)
0.5%
V
RIPPLE1
Output ripple I
OUT1
= I
OUT1(max)
24 mV
V
OVER1
Output overshoot ΔI
OUT1
= 5 A 40 mV
V
UNDER1
Output undershoot ΔI
OUT1
= 5A 40 mV
I
OUT1
Output current V
IN(min)
≤ V
IN
≤ V
IN(max)
0 10 A
I
SCP1
Short circuit current trip point 15 A
OUTPUT 2 CHARACTERSTICS
V
OUT2
Output voltage I
OUT2(min)
≤ I
OUT2
≤ I
OUT2(max)
1.8 V
Line regulation V
IN(min)
≤ V
IN
≤ V
IN(max)
0.5%
Load regulation I
OUT2(min)
≤ I
OUT2
≤ I
OUT2(max)
0.5%
V
RIPPLE2
Output ripple I
OUT2
= I
OUT2(max)
36 mV
V
OVER2
Output overshoot ΔI
OUT2
= 5 A 40 mV
V
UNDER2
Output undershoot ΔI
OUT2
= 5 A 40 mV
I
OUT2
Output current V
IN(min)
≤ V
IN
≤ V
IN(max)
0 10 A
I
SCP2
Short circuit current trip point 15 A
GENERAL CHARACTERSTICS
t
SS
Soft-start time V
IN
= 12 V 2 ms
η Efficiency V
IN
= 12 V, I
OUT1
= I
OUT2
= 10 A 88%
f
SW
Switching frequency 500 kHz
Design Procedure
Equations and calculations are shown regarding V
OUT1
. V
OUT2
values can be calculated using similar equations.
Selecting a Switching Frequency
To maintain acceptable efficiency and meet minimum on-time requirements, a 500kHz 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 a target ripple current of 30%, the required inductor size, at maximum rated output current, can
be calculated using Equation 8.
(8)
Selecting a standard, readily available inductor, with a rated inductance is 0.88 µH at 10 A, I
RIPPLE1
= 2.5 A
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