Texas Instruments TPS40003 User Manual

User’s Guide

TPS40003 Based 5–A Converter in
Less Than One Square Inch

User’ s Gu ide

EVM IMPORTANT NOTICE

Texas Instruments (TI) provides the enclosed product(s) under the following conditions:
This evaluation kit being sold by TI is intended for use for ENGINEERING DEVELOPMENT OR EVALUATION

PURPOSES ONLY and is not considered by TI to be fit for commercial use. As such, the goods being provided
may not be complete in terms of required design-, marketing-, and/or manufacturing-related protective
considerations, including product safety measures typically found in the end product incorporating the goods.
As a prototype, this product does not fall within the scope of the European Union directive on electromagnetic
compatibility and therefore may not meet the technical requirements of the directive.

Should this evaluation kit not meet the specifications indicated in the EVM User’s Guide, the kit may be returned
within 30 days from the date of delivery for a full refund. THE FOREGOING WARRANTY IS THE EXCLUSIVE
WARRANTY MADE BY SELLER TO BUYER AND IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED,
IMPLIED, OR S TA TUTOR Y, INCLUDING ANY WARRANTY OF MERCHANTABILITY OR FITNESS FOR ANY
PARTICULAR PURPOSE.

The user assumes all responsibility and liability for proper and safe handling of the goods. Further, the user
indemnifies TI from all claims arising from the handling or use of the goods. Please be aware that the products
received may not be regulatory compliant or agency certified (FCC, UL, CE, etc.). Due to the open construction
of the product, it is the user’s responsibility to take any and all appropriate precautions with regard to electrostatic
discharge.

EXCEPT TO THE EXTENT OF THE INDEMNITY SET FORTH ABOVE, NEITHER PARTY SHALL BE LIABLE
TO THE OTHER FOR ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES.

TI currently deals with a variety of customers for products, and therefore our arrangement with the user is not
exclusive.

TI assumes no liability for applications assistance, customer product design, software performance, or
infringement of patents or services described herein.

Please read the EVM User’s Guide and, specifically, the EVM Warnings and Restrictions notice in the EVM
User’s Guide prior to handling the product. This notice contains important safety information about temperatures
and voltages. For further safety concerns, please contact the TI application engineer.

Persons handling the product must have electronics training and observe good laboratory practice standards.
No license is granted under any patent right or other intellectual property right of TI covering or relating to any

machine, process, or combination in which such TI products or services might be or are used.

Mailing Address:

Texas Instruments
Post Office Box 655303
Dallas, Texas 75265

Copyright  2003, Texas Instruments Incorporated

2

DYNAMIC WARNINGS AND RESTRICTIONS

It is important to operate this EVM within the input voltage range of 0 V to 5.5 V.
Exceeding the specified input range may cause unexpected operation and/or irreversible damage to the EVM.

If there are questions concerning the input range, please contact a TI field representative prior to connecting
the input power.

Applying loads outside of the specified output range may result in unintended operation and/or possible
permanent damage to the EVM. Please consult the EVM User’s Guide prior to connecting any load to the EVM
output. If there is uncertainty as to the load specification, please contact a TI field representative.

During normal operation, some circuit components may have case temperatures greater than 50°C. The EVM
is designed to operate properly with certain components above 50°C as long as the input and output ranges are
maintained. These components include but are not limited to linear regulators, switching transistors, pass
transistors, and current sense resistors. These types of devices can be identified using the EVM schematic
located in the EVM User’s Guide. When placing measurement probes near these devices during operation,
please be aware that these devices may be very warm to the touch.

Mailing Address:

Texas Instruments
Post Office Box 655303
Dallas, Texas 75265

Copyright  2003, Texas Instruments Incorporated

3

SLUU130A – September 2002 – Revised February 2003

r

TPS40003-Based 5-A Converter in Less Than One Square

Inch

Mark Dennis Systems Powe

Contents

1 Introduction 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2 Features 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3 Schematic 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4 Design Procedure 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5 PowerPAD Packaging 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6 Test Results/Performance Data 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7 PCB Layout 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8 List of Material 16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 Introduction

The TPS40002 and the TPS40003 are voltage-mode, synchronous buck PWM controllers that utilize TI’s
proprietary Predictive Gate Drive technology to wring maximum efficiency from step-down converters. These
controllers provide a bootstrap charging circuit to allow the use of an N-channel MOSFET as the topside buck
switch to reduce conduction losses and increase silicon device utilization. Predictive Gate Drive technology
controls the delay from main switch turn-off to synchronous rectifier turn-on and also the delay from rectifier
turn-off to main switch turn-on. This allows minimization of the losses in the MOSFET body diodes by reducing
conduction and reverse recovery time. This user’s guide provides details on a 5-A buck converter that converts

3.3 V down to a 1.2-V level utilizing the TPS40003 controller, with less than one square inch board area.
A schematic for the board is shown in Figure 1. A list of material is provided in the final section.

2 Features

The specification for this board is as follows:

D V
D V
D 0 A ≤ I
D Efficiency > 90% with a load of 2 A
D Output voltage ripple < 2% V
D Physical size < 1 square inch circuit area

= 3.0 V to 3.6 V

IN

= 1.2 V ± 3%

OUT

≤ 5 A

OUT

OUT

4

TPS40003-Based 5-A Converter in Less Than One Square Inch

3 Schematic

SLUU130A – September 2002 – Revised February 2003

+

Figure 1. Application Diagram for the TPS40002/3

TPS40003-Based 5-A Converter in Less Than One Square Inch

5

SLUU130A – September 2002 – Revised February 2003

4 Design Procedure

4.1 TPS4000X Family Device Selection

The TPS4000X family of devices offers four selections to encompass the frequency and output current mode
choices. The TPS40003 is selected for the following reasons. First, the internal oscillator components set a fixed
switching frequency of 600 kHz. This allows minimally sized filter components in this compact design. The other
choice related to the TPS4000X family involves the selection of Discontinuous Current Mode (DCM) operation
or Continuous Current Mode (CCM) operation at lighter loads. In this design the TPS40003 is selected to keep
the current continuous all the way to zero load, to provide robust control characteristics.

4.2 Inductance Value

The output inductor value is selected to set the ripple current to a value most suited to overall circuit functionality.
The inductor value is calculated in equation (1).

L +

where I

V

f I

RIPPLE

OUT
RIPPLE

ȡ
ȧ
Ȣ

is chosen to be 25% of I

1 *

V

OUT

V

IN(max)

ȣ

+

ȧ

600 kHz 1.25 A

Ȥ

OUT

1.2 V

, or 1.25 A. A common value of 1 µH is selected.

ǒ

1 *

1.2 V

3.6 V

Ǔ

+ 1.07 mH

4.3 Input Capacitor Selection

Bulk input capacitor selection is based on allowable input voltage ripple and required RMS current carrying
capability. In typical buck converter applications, the converter is fed from an upstream power converter with
its own output capacitance. In this converter, onboard capacitance is provided to supply the current required
during the top MOSFET on-time while keeping ripple within acceptable limits. For this power level, input voltage
ripple of 150 mV is reasonable, and a conservative minimum value of capacitance is calculated in equation (2).

I Dt

C +

To meet this requirement with the lowest size and cost, a single 22 µF, X5R ceramic capacitor might be
considered. Although these capacitors have an extremely small resistance a typical datasheet indicates that
the part undergoes a 30°C temperature rise with 2 A
nearly 2 A
current derating. These capacitors function as power bypass components and should be located near the
MOSFET package, to keep the high frequency current flow in a tight loop. The low impedance characteristics
of the dual ceramic capacitors help to reduce noise on the V
MOSFET current sense is referenced to this point, so noise at the device must be kept to a low level.

DV

RMS

5A 606 ns

+

of current, so for a conservative design two capacitors are selected to allow for conservative

0.15 V

+ 20 mF

current at 500 kHz. With V

RMS

supply of the device. Specifically , the high side

DD

= 3.0 V our circuit requires

IN

(1)

(2)

6

TPS40003-Based 5-A Converter in Less Than One Square Inch