Microsemi LX7175 Manual de usuario

LX7175

User Guide

LX7175 3 Amp Step-Down Converter Evaluation Board

LX7175 User Guide Revision 2.0

Contents

1 Revision History ............................................................................................................................. 1

1.1 Revision 1.0 ........................................................................................................................................ 1

2 Product Description ....................................................................................................................... 2

2.1 Applications ........................................................................................................................................ 2

2.2 Key Features ....................................................................................................................................... 2

3 Evaluation Board Schematic .......................................................................................................... 3

4 Basic Connection Instructions ........................................................................................................ 4

5 Recommended Operating Conditions ............................................................................................ 5

5.1 Mode Selection ................................................................................................................................... 5

5.2 Setting the Output Voltage ................................................................................................................. 5

6 PCB Layout of Evaluation Board ..................................................................................................... 6

7 Bill of Materials ............................................................................................................................ 11

8 Efficiency Plot ............................................................................................................................... 12

9 Dynamic Load Response Scope Shots .......................................................................................... 13

10 Start-up Scope Shots ................................................................................................................... 14

10.1 Start-up with Enable Toggled ......................................................................................................... 14

10.2 Power-up with No Load (EN Tied to 5 V VIN, PWM) ...................................................................... 15

10.3 Power-up with Resistive Load (EN Tied to 5 V VIN, PWM) ............................................................. 16

10.4 Power-up with No Load (EN Tied to 5 V VIN, PSM) ........................................................................ 17

11 Ordering Information .................................................................................................................. 18

LX7175 3 Amp Step-Down Converter Evaluation Board

LX7175 User Guide Revision 2.0 1

1 Revision History

The revision history describes the changes that were implemented in the document. The changes are

listed by revision, starting with the most current publication.

1.1 Revision 1.0

Revision 1.0 was published in August 2017. It was the first publication of this document.

LX7175 3 Amp Step-Down Converter Evaluation Board

LX7175 User Guide Revision 2.0 2

2 Product Description

The LX7175 is a step-down pulse-width modulation (PWM) switching regulator IC with integrated high

side P-CH and low side N-CH MOSFETs. The IC operates using a hysteretic control topology with a full

load switching frequency of 1.4 MHz, allowing small output filter components while maintaining

excellent dynamic load response.

The operational input voltage range of the LX7175 is from 3 V to 5.5 V and it has two modes of

operation selected externally by the MODE pin. When the MODE pin is high, the device operates in

continuous PWM operation, and when it is tied low, it operates in power wave mode (PSM) with

automatic transition between PWM and PSM mode depending on the load current. This allows the

converter’s efficiency to remain high when load current drops.

Other features include cycle-by-cycle current limit followed by latch off, thermal protection with

hysteresis, internal digital soft start, and Power Good function.

2.1 Applications

Small battery-operated devices

Hard disk drives (HDDs)

Set-top boxes

LCD TVs

Notebooks/Netbooks

Routers

Video cards

PC peripherals

PoE-powered devices

2.2 Key Features

3 A step-down regulator

Operational input supply voltage range: 3 V–5.5 V

Integrated PMOS and NMOS

Load current from 0 A to 3 A

1.4 MHz switching frequency

SKIP pulse to improve light load efficiency

Open VReg Type 0 LV compatible

Input UVLO protection

Enable pin

Power good

Internal soft start

Cycle-by-cycle over current protection

Latch-off operation under output short

RoHS-compliant (Pb-free)

LX7175 3 Amp Step-Down Converter Evaluation Board

LX7175 User Guide Revision 2.0 3

3 Evaluation Board Schematic

The following illustration shows the evaluation board schematic.

Figure 1 • Schematic of Evaluation Board

LX7175 3 Amp Step-Down Converter Evaluation Board

LX7175 User Guide Revision 2.0 4

4 Basic Connection Instructions

The following illustration shows how to connect the evaluation board to the power supply.

Figure 2 • Power Supply and Load Connection

LX7175 3 Amp Step-Down Converter Evaluation Board

LX7175 User Guide Revision 2.0 5

5 Recommended Operating Conditions

The following table lists the operating conditions for the LX7175 Evaluation Board.

Table 1 • Operating Conditions

Description Symbol Minimum Maximum Unit

Input voltage VIN 3 5.5 V

Output current IOUT 0 3 A

Operating ambient temperature TA–10 85 °C

Enable chip EN VIN

Shut down chip EN Pull to GND

5.1 Mode Selection

Mode Jumper set to HI means PWN or mode = 1. Mode jumper set to LOW means power save mode

(PSM), or

mode = 0.

5.2 Setting the Output Voltage

In case a different output voltage is needed, it must be programmed through an external resistor divider

connected from SW to V and then to GND. For noise immunity, the lower resistor R2 from V to OUT OUT

GND should be greater than 100 kΩ. A feed-forward capacitor C9 in parallel with the upper resistor is

needed to ensure loop stability. It is recommended that C9 = 120 pF. The following formula gives the

value of V .OUT

Where V = 0.8 V.REF

LX7175 3 Amp Step-Down Converter Evaluation Board

LX7175 User Guide Revision 2.0 6

6 PCB Layout of Evaluation Board

The LX7175 Evaluation Board is a four-layer board. The following illustrations depict each of the board's

four layers.

Figure 3 • Top Silkscreen

LX7175 3 Amp Step-Down Converter Evaluation Board

LX7175 User Guide Revision 2.0 7

Figure 4 • Layer 1: Top Layer

LX7175 3 Amp Step-Down Converter Evaluation Board

LX7175 User Guide Revision 2.0 8

Figure 5 • Layer 2: Inner Layer 1

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