Texas Instruments HPA070 User Manual

User’s Guide

TPS40055-Based Design Converts 12-V Bus to 1.8 V at 15 A (HPA070)

User’ s Gu ide

EVM IMPORTANT NOTICE

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DYNAMIC WARNINGS AND RESTRICTIONS

It is important to operate this EVM within the input voltage range of 0 V

to 14 VDC.

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

SLUU186 − March 2004

TPS40055-Based Design Converts 12-V Bus to

1.8 V at 15 A (HPA070)

Mark Dennis System Pow

Contents

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

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

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

4 Component Selection 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5 Test Setup 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6 Test Results and Performance Data 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7 EVM Assembly Drawing and PCB Layout 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8 List of Materials 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9 References 16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 Introduction

In many modern electronic applications there is a growing demand for circuits to convert a12-V bus to digital voltages as low as, but not limited to 1.8 V. The current requirements can range from below 1 A to over 15 A. For high-efficiency and small circuit size the TPS40055 wide-input synchronous buck controller can be used to provide the necessary control and drive functions to implement these converters. The TPS40055EVM−001 operates at 300 kHz and delivers 1.8 V at 15 A with efficiency over 90% for much of the load range, and a full load efficiency of 88%.

The TPS40055 synchronous buck controller offers a variety of user programmable functions such as operating frequency, soft-start time, voltage feed-forward, high-side current limit, and external loop compensation. This controller also provides a regulated 10-V bias voltage which supplies onboard drivers for the N-channel switch and synchronous rectifier MOSFET s, utilizing adaptive gate drive logic to prevent cross conduction of the power MOSFETs.

[1]

2 Features

The specification of this design is as follows:

D 92% peak efficiency at 6 A D 88% peak efficiency at 15 A D 1.8V output at 15 A D V D Small circuit size 1.4” x 2.5” SMT design, components on single side

range from 10 VDC to 14 V

D Line/load regulation < 0.5% D High-frequency 300-kHz operation D Transient deviation 60 mV with 10-A load step

TPS40055-Based Design Converts 12-V Bus to 1.8 V at 15 A (HPA070)

3 Schematic

SLUU186 − March 2004

Figure 1. TPS40055EVM−001 (HPA070) Schematic

TPS40055-Based Design Converts 12-V Bus to 1.8 V at 15 A (HPA070)

SLUU186 − March 2004

(1)

(2)

4 Component Selection

4.1 TPS40055 Device Selection

The TPS4005x family of parts offers a range of output current configurations including source only (TPS40054), source/sink (TPS40055), or source/sink with V source/sink capability is selected. This serves to maintain continuous inductor ripple current all the way to zero load to improve the small signal loop response by preventing the inductor current from transitioning to the discontinuous current mode.

The TPS4005x family is packaged in TI’s PWP PowerPAD thermally enhanced package which should be soldered to the PCB using standard solder flow techniques. The PowerPAD technology uses a thermally conductive epoxy to attach the integrated circuit die to the leadframe die pad, which is exposed on the bottom of the completed package. The PWP PowerPAD package has a θ temperature rise relatively low even with the power dissipation inherent in the onboard MOSFET drivers. This power loss is proportional to switching frequency, drive voltage, and the gate charge needed to enhance the N-channel MOSFETs. Effective heat removal allows the use of ultra-small packaging while maintaining high component reliability.

The technical brief, PowerPAD Thermally Enhanced Package package.

4.2 Frequency of Operation

prebias (TPS40057). In this converter the TPS40055 with

OUT

= 2°C/W which helps keep the junction

[2]

contains more information on the PowerPAD

The clock oscillator frequency for the TPS40055 is programmed with a single resistor from RT (pin 2) to signal ground. The following equation (1) from the datasheet allows selection of RT in kΩ for a given switching frequency in kHz.

RT+ R2 +

For 300-kHz operation, R2 is selected to be 165 kΩ. For a particular operating frequency, the PWM ramp time must be programmed via the resistor R

to V

. Also, the selection of R

the circuit from starting at low voltages, which can lead to current flow larger than desired. R using equation (2).

+ R6 +ǒV

KFF

Where V incorporated into this equation, so the actual V frequency of 300-kHz, the R

IN(min)

is the minimum startup input voltage, and RT is in kΩ. Note that internal tolerances have been

17.82 10

programs the VIN voltage at which the circuit starts operation. This prevents

KFF

IN(min)

* 3.5

value of 71.5 kΩ is selected.

KFF

* 23 (kW)

58.14 RT) 1340

IN(min)

connected

KFF

is programmed

KFF

(kW)

of the input voltage should be used. For an oscillator

TPS40055-Based Design Converts 12-V Bus to 1.8 V at 15 A (HPA070)

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