Microsemi LX7175 User Manual

LX7175

User Guide

LX7175 3 Amp Step-Down Converter Evaluation Board

LX7175 3 Amp Step-Down Converter Evaluation Board

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

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LX7175 3 Amp Step-Down Converter Evaluation Board

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.

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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)

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3 Evaluation Board Schematic

The following illustration shows the evaluation board schematic.

Figure 1 • Schematic of Evaluation Board

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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

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LX7175 3 Amp Step-Down Converter Evaluation Board

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

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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

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Figure 4 • Layer 1: Top Layer

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Figure 5 • Layer 2: Inner Layer 1

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Figure 6 • Layer 3: Inner Layer 2

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Figure 7 • Layer 4: Bottom Layer

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7 Bill of Materials

The following table lists the bill of materials (BOM) for the LX7175 Evaluation Board.

Table 2 • BOM

Item Part Type Specification Reference Quantity

1 Miscellaneous

component

Microsemi IC—LX7175 U1 1

2 Miscellaneous

component

Test point SW, PGOOD, VINSENSE, VOSENSE,

GNDSENSE, GNDSENSE, FB, MODE

8

3 Miscellaneous

component

Terminal VIN, VOUT, GND, GND 4

4 Miscellaneous

component

Jumper/3 pin J1, J2 2

5 Capacitor 1 µF C2 1

6 Capacitor 0 Ω C1, C3 2

7 Capacitor 100 kΩ C4 1

8 Capacitor 22 µF/6.3 V/X5R C5, C6 2

9 Resistor 0 Ω R4 1

10 Resistor 100 kΩ R3 1

11 Resistor 49.9 kΩ 1% R1 1

12 Resistor 200 kΩ 1% R2 1

13 Inductor 1 µH – ESR = 10 mΩ L1 1

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8 Efficiency Plot

The following graph shows the efficiency of the LX7175 at a voltage output of 1 V.

Figure 8 • Efficiency Plot of LX7175

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9 Dynamic Load Response Scope Shots

The following graph shows the board's dynamic load response, PWM.

Figure 9 • Dynamic Load Response With 1 A–3 A Load, PWM

CH2: VOUT, CH4: load current

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LX7175 3 Amp Step-Down Converter Evaluation Board

10 Start-up Scope Shots

The following graphs show the scope shots for the LX7175.

10.1 Start-up with Enable Toggled

The following graph shows startup with ENABLE toggled.

Figure 10 • Start-up with ENABLE Toggled

CH1: V , CH2: V , CH3: PGOOD, CH4: inductor current.IN OUT

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

The following graph shows power-up with no load.

Figure 11 • Power-up with No Load

CH1: V , CH2: V , CH3: PGOOD, CH4: inductor current.IN OUT

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LX7175 3 Amp Step-Down Converter Evaluation Board

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

The following graph shows power-up with resistive load.

Figure 12 • Power-up with Resistive Load (EN Tied to 5 V VIN, PWM)

CH1: V , CH2: V , CH3: PGOOD, CH4: inductor current.IN OUT

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

The following graph shows power-up with no load.

Figure 13 • Power-up with No Load (EN Tied to 5 V VIN, PSM)

CH1: V , CH2: V , CH3: PGOOD, CH4: inductor current.IN OUT

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11 Ordering Information

The following table lists the ordering information for the LX7175 evaluation board and IC.

Table 3 • Ordering Information

Part Order Number Description

LX7175CLD DFN 3 mm × 3 mm 10-layer integrated circuit

LX7175 SE EVALUATION BOARD Evaluation PCB for LX7175

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LX7175 3 Amp Step-Down Converter Evaluation Board

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