TPS40322 datasheet(21/40 Pages) TI1

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IN(max)

OUT1

IN(max)

15 V

1.2 V

0.736 H

0.3

10 A

15 V

500 kHz

TPS40322

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SLUSAF8

– JUNE 2011

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 2.

Table 2. TPS40322 Dual Output Design Example Specification

PARAMETER

TEST CONDITION

MIN

NOM

MAX

UNIT

INPUT CHARACTERSTICS

VIN

Input voltage

VIN(ripple)

Input ripple

IOUT1 = IOUT2 = 10 A

0.25

OUTPUT 1 CHARACTERSTICS

VOUT1

Output voltage

IOUT1(min) ≤ IOUT1 ≤ IOUT1(max)

1.2

Line regulation

VIN(min) ≤ VIN ≤ VIN(max)

0.5%

Load regulation

IOUT1(min) ≤ IOUT1 ≤ IOUT1(max)

0.5%

VRIPPLE1

Output ripple

IOUT1 = IOUT1(max)

VOVER1

Output overshoot

ΔIOUT1 = 5 A

VUNDER1

Output undershoot

ΔIOUT1 = 5A

IOUT1

Output current

VIN(min) ≤ VIN ≤ VIN(max)

ISCP1

Short circuit current trip point

OUTPUT 2 CHARACTERSTICS

VOUT2

Output voltage

IOUT2(min) ≤ IOUT2 ≤ IOUT2(max)

1.8

Line regulation

VIN(min) ≤ VIN ≤ VIN(max)

0.5%

Load regulation

IOUT2(min) ≤ IOUT2 ≤ IOUT2(max)

0.5%

VRIPPLE2

Output ripple

IOUT2 = IOUT2(max)

VOVER2

Output overshoot

ΔIOUT2 = 5 A

VUNDER2

Output undershoot

ΔIOUT2 = 5 A

IOUT2

Output current

VIN(min) ≤ VIN ≤ VIN(max)

ISCP2

Short circuit current trip point

GENERAL CHARACTERSTICS

tSS

Soft-start time

VIN = 12 V

Efficiency

VIN = 12 V, IOUT1= IOUT2 = 10 A

88%

fSW

Switching frequency

500

kHz

Design Procedure

Equations and calculations are shown regarding VOUT1. VOUT2 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

(IRIPPLE). 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, IRIPPLE1 = 2.5 A

TPS40322 Datasheet(PDF) 21 Page - Texas Instruments

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