Texas Instruments AN-2281 LMR61428 Evaluation Module (Rev. A) User guide

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Texas Instruments AN-2281 LMR61428 Evaluation Module (Rev. A) User guide | Manualzz

User's Guide

SNVU193A – October 2012 – Revised April 2013

AN-2281 LMR61428 Evaluation Module

1

2

3

Introduction

The LMR61428 evaluation module is designed to provide the power supply design engineer with a fully functional regulator design. The evaluation module takes the input from a single Li-Ion battery and boosts the voltage up to 5V at a constant load capability of 500mA. The switching frequency of the boost regulator is set to about 1200 kHz which helps in reducing the solution size and keeping switching noise out of the AM radio band. The printed circuit board consists of 4 layers of copper on FR4 material. The first middle layer is a solid ground layer which helps in minimizing the AC current loop. This user's guide contains the evaluation module schematic, a quick setup procedure using a bench power supply, and a

Bill-of-Materials (BOM). For complete circuit design information, see LMR61428 SIMPLE SWITCHER

14Vout, 2.85A Step-Up Voltage Regulator in VSSOP ( SNVS815 ).

Features

• One cell Li-Ion battery for Input Voltage

• 5V Output Voltage at 500mA Output Current

• Switching Frequency of 1.2 MHz

• Small Solution Size: 2.287 × 1.058 inches (58.09 × 26.87 mm)

Evaluation Board Schematic

1 Cell Li-ion

VIN

30203001

3

2

1

J1

+

Cin

Cboot

L1

SW D1

U1

7

BOOT SW

8

Rdd

Cdd

Ren

Rt

EN

2

6

LMR61428

EN

VDD

4

FB

PGND

1

GND

3

FREQ SGND

5

Rfbt

Rfbb

Cff

5V at 0.5A

VOUT

+

Co1

Co2

GND

Figure 1. LMR61428 Evaluation Module Schematic

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SNVU193A – October 2012 – Revised April 2013

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1

Powering and Loading Considerations

4 Powering and Loading Considerations

Read this entire section prior to attempting to power the evaluation board.

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4.1

Quick Start Procedure

Step 1: Set the bench power supply current limit to 3A. Set the power supply voltage to 3.5V. Turn off the power supply output. Connect the power supply to the LMR61428 demo board. Positive connection to V

IN and negative connection to GND.

Step 2: Connect a load, as high as 0.5A, to the V

OUT connection to GND.

terminal. Positive connection to V

OUT and negative

Step 3: Connect the shunt so as to short the pins 1 and 2 of the jumper J1. This sets the bootstrap to V

OUT

Step 4: The EN pin should be left open for normal operation.

Step 5: Turn on the bench power supply with no load applied to the LMR61428. If the shunt for the jumper

J1 was in place, the V

OUT would be in regulation at a nominal 5V.

Step 6: Gradually increase the load and V

OUT

0.5 Amps.

should remain in regulation as the load is increased up to

4.2

Shutdown Operation

The EVM includes a pull-up resistor Ren to enable the device. Use the EN post to disable the device by pulling this node to GND.

4.3

Bootstrap Operation

The EVM has a jumper installed to select the bootstrap option. The default condition is that the jumper be set such that the bootstrap voltage is obtained from the output. For more information, see LMR61428

SIMPLE SWITCHER 14Vout, 2.85A Step-Up Voltage Regulator in VSSOP ( SNVS815 ).

4.4

Setting the Output Voltage

The output voltage of the step-up regulator can be set between 1.24V and 14V. But because of the gated oscillator scheme, the maximum possible input to output boost ratio is fixed. For a boost regulator,

V

OUT

/ V

IN

= 1 / [1 − D] (1)

The LMR61428 has a fixed duty cycle, D, of 70% typical. Therefore,

V

OUT

/ V

IN

= 1 / 0.3

(2)

This sets the maximum possible boost ratio of V

IN to V

OUT to about 3 times. The user can now estimate what the minimum design inputs should be in order to achieve a desired output, or what the output would be when a certain minimum input is applied. For example, if the desired V

OUT should be higher than V

OUT was 14V, then the least V

/ 3. If the input voltage fell below this threshold, the output voltage would not

IN be regulated because of the fixed duty cycle. If the minimum V

V

OUT would be V

IN

× 3.

IN was guaranteed at 2V, the max possible

The V

OUT is set by connecting a feedback resistive divider made of R values are selected as follows: fbt and R fbb

. The feedback resistor

R fbb

= R fbt

/[(V

OUT

/ 1.24)

1] (3)

A value of 150k Ω is suggested for R fbt

. Then, R fbb can be selected using

Equation 3 . A 39pF capacitor (C

ff

) connected across R fbt helps in feeding back most of the AC ripple at V

OUT to the FB pin. This helps reduce the peak-to-peak output voltage ripple as well as improve the efficiency of the step-up regulator, because a set hysteresis of 30mV at the FB pin is used for the gated oscillator control scheme.

2

AN-2281 LMR61428 Evaluation Module

SNVU193A – October 2012 – Revised April 2013

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4.5

Typical Test Setup

Powering and Loading Considerations

Electronic

Load +

-

Ammeter

A

Ammeter

VOUT GND GND VIN

A

-

+

Power

Supply

Voltmeter

V V

Voltmeter

Demo Board

Figure 2. Efficiency Measurements

Oscilloscope

VOUT GND

Chf

Figure 3. Voltage Ripple Measurements

SNVU193A – October 2012 – Revised April 2013

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3

Powering and Loading Considerations

I

I

I

I

I

I

I

I

I

I

I

I

VIN GND VOUT

1 2 3 4 5 6

A B C D E F

Figure 4. Edge Connector Schematic

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4

AN-2281 LMR61428 Evaluation Module

SNVU193A – October 2012 – Revised April 2013

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4.6

Board Images

Powering and Loading Considerations

Figure 5. Top Side

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Powering and Loading Considerations

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Figure 6. Bottom Side

6

AN-2281 LMR61428 Evaluation Module

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5 Typical Performance Characteristics

84

Efficiency vs. Load Current

V

OUT

= 5V

82

80

78

76

74

72

70

68

66

Vin = 3.0V

Vin = 3.1V

Vin = 3.2V

Vin = 3.4V

Vin = 3.5V

Vin = 3.6V

Vin = 3.8V

Vin = 4.0V

64

0.000.060.120.180.240.300.360.420.480.54

IOUT(A)

Switching Node and Output Voltage Waveforms

V

IN

= 3.6V, I

OUT

= 500mA

V

SW

5V/Div

V

OUT

= 5V

50 mV/Div

10

P s/DIV

Typical Performance Characteristics

V

Load Transient Waveforms

IN

= 3.6V, I

OUT

= 50 to 500mA

I

OUT

100 mA/Div

V

OUT

= 5V

50 mV/Div

100

P s/DIV

Startup Waveform

V

OUT

= 5V

2V/Div

I

OUT

= 0.5A

0.5A/Div

V

IN

= 3V

1V/Div

500

P s/DIV

SNVU193A – October 2012 – Revised April 2013

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7

Bill of Materials

6 Bill of Materials

Co1

Co2

Cdd

Cff

Rfbt

Rfbb

Rt

Rdd

Ren

EN

VIN

VOUT

GND

SW

J1

ID

U1

L1

D1

Cin

Part Number

LMR61428

SRU1048-8R2Y

B220A-13-F

293D226X9010C2TE3

594D686X0010C2T

08053D105KAT2A

C0603C105K4PACTU

GRM1885C2A390JA01D

RG1608P-154-B-T5

RG1608P-4992-B-T5

CRCW0603118KFKEA

CRCW060349R9FKEA

CRCW060310K0FKEA

5014

5010

5013

5011

5012

PBC03SAAN

Type

Boost Regulator

Inductor

Diode

Capacitor

Capacitor

Capacitor

Capacitor

Capacitor

Resistor

Resistor

Resistor

Resistor

Resistor

Test Point Loop

Test Point Loop

Test Point Loop

Test Point Loop

Test Point Loop

Header

SH-J1 969102-0000-DA Shunt www.ti.com

SMD

0805

0603

0603

0603

0603

0603

0603

0603

Size

SOT-23

SMD

SMA

SMD

Parameters

8.2uH, 4.6A,

0.015 ohm,

Schottky, 20V, 2A

Tantalum, 22uF,

10V

Tantalum, 68uF,

10V

Ceramic, 1uF,

25V, X5R

Ceramic, 1uF,

16V, X5R

Ceramic, 39pF,

100V, C0G/NP0

150 k Ω

49.9 k Ω

118 k Ω

49.9

10.0 k Ω

Yellow

Red

Orange

Black

White

100mil, 1x3

Qty

1

1

1

1

1

1

2

1

1

1

1

1

1

1

1

1

1

1

1

100mil, Black 1

Vendor

Texas

Instruments

Bourns

Toshiba

Vishay-

Sprague

Vishay-

Sprague

AVX

Kemet

MuRata

Susumu Co Ltd

Susumu Co Ltd

Vishay-Dale

Vishay-Dale

Vishay-Dale

Keystone

Keystone

Keystone

Keystone

Keystone

Sullins

Connector

Solutions

3M

8

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7 PCB Layout

PCB Layout

Figure 7. Top Copper

Figure 8. Top Overlay

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9

PCB Layout

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Figure 9. Internal Layer 1

Figure 10. Internal Layer 2

10

AN-2281 LMR61428 Evaluation Module

SNVU193A – October 2012 – Revised April 2013

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www.ti.com

PCB Layout

Figure 11. Bottom Copper

Figure 12. Bottom Overlay

SNVU193A – October 2012 – Revised April 2013

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AN-2281 LMR61428 Evaluation Module

Copyright © 2012–2013, Texas Instruments Incorporated

11

IMPORTANT NOTICE

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TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI’s terms and conditions of sale of semiconductor products. Testing and other quality control techniques are used to the extent TI deems necessary to support this warranty. Except where mandated by applicable law, testing of all parameters of each component is not necessarily performed.

TI assumes no liability for applications assistance or the design of Buyers’ products. Buyers are responsible for their products and applications using TI components. To minimize the risks associated with Buyers’ products and applications, Buyers should provide adequate design and operating safeguards.

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