Microsemi LX7178 Manuel utilisateur

LX7178 EVAL BOARD USER GUIDE

Microsemi

Analog Mixed Signal Group

One Enterprise Aliso Viejo, CA 92656 USA (800) 713-4113, (949) 380-6100

Rev. 0.1, 2013-10-23

Rev. 1.0, 2013-10-23

LX7178 EVALUATION BOARD

USER GUIDE

LX7178 5 Amp Step Down Converter

LX7178 EVAL BOARD USER GUIDE

Microsemi

Analog Mixed Signal Group

One Enterprise Aliso Viejo, CA 92656 USA (800) 713-4113, (949) 380-6100

Rev. 0.1, 2013-10-23

Rev. 1.0, 2013-10-23

Table of Contents

Introduction to Product ..............................................................................................1

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

Applications ...............................................................................................................2

Part Specific Information...........................................................................................3

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

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

LX7178 I2C GUI........................................................................................................5

Recommended Operating Conditions........................................................................6

PCB Layout of Evaluation Board..............................................................................7

Bill of Material.........................................................................................................11

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

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

Dynamic Load Response Scope Shots (Continue)..................................................14

Start up and Short Condition Scope Shots...............................................................15

Start up and Short Condition Scope Shots (Continue) ............................................16

Dimax Sub20 Installation ........................................................................................17

LX7178 EVAL BOARD USER GUIDE

Microsemi

Analog Mixed Signal Group

One Enterprise Aliso Viejo, CA 92656 USA (800) 713-4113, (949) 380-6100

Page 1

Rev. 0.1, 2013-10-23

Rev. 1.0, 2013-10-23

Introduction to Product

The LX7178 is a digitally controlled step-down regulator IC with an integrated 40mΩ high-side P-

channel MOSFET and a 14mΩ low-side N-channel MOSFET. It features Microsemi’s proprietary

constant-frequency hysteretic control engine for near-instantaneous correction to line/load

transients. It does not require high-ESR output capacitors and incorporates energy-saving “PSM”

(Power Save or Pulse Skip Mode) at light loads, to extend battery life in mobile applications.

The LX7178 has an I2C serial interface port for output voltage margining and monitoring if

required (it can also operate in default mode). In addition it includes robust fault monitoring

functions.

The LX7178 will operate from 3V to 5.5V, and is available in a fixed output voltage option of

0.8V (no voltage divider is necessary). The output voltage can also be adjusted with an external

voltage divider up to 3.3V.

LX7178 EVAL BOARD USER GUIDE

Microsemi

Analog Mixed Signal Group

One Enterprise Aliso Viejo, CA 92656 USA (800) 713-4113, (949) 380-6100

Page 2

Rev. 0.1, 2013-10-23

Rev. 1.0, 2013-10-23

Key Features

Constant Frequency Hysteretic Control

Extremely Fast Line/Load Transient Response

I2C for Output Adjustment (3.4Mbps)

1.875MHz Switching Frequency

Extremely Low-RDSON MOSFETS

Input Voltage Rail 3.3V to 5V, Current 5A

I2C Selectable Power Save Mode for Light-Load Efficiency

UVLO, OVP, OCP

0°C to +85°C Ambient Temperature

Available in WLCSP-20 (0.4mm pitch)

RoHS Compliant

Applications

High Performance HDD

Notebook/ Netbook

Tablets/ Slates

LX7178 EVAL BOARD USER GUIDE

Microsemi

Analog Mixed Signal Group

One Enterprise Aliso Viejo, CA 92656 USA (800) 713-4113, (949) 380-6100

Page 3

Rev. 0.1, 2013-10-23

Rev. 1.0, 2013-10-23

Part Specific Information

IC Part Number

Description

LX7178-xyCSP

WLCSP 20Ball 0.4mm Pitch

Note: “x” is the 2 LSB bits of the binary I2C slave address (0 to 3);

“y” is the set output voltage (0 is 0.6V, 1 is 0.8V, 2 is 0.9V, 3 is 0.975V)

Evaluation Board Part Number

Description

LX7178 EVAL BOARD

Evaluation PCB for LX7178

Evaluation Board Schematic

Figure 1: Schematic of Evaluation Board

LX7178 EVAL BOARD USER GUIDE

Microsemi

Analog Mixed Signal Group

One Enterprise Aliso Viejo, CA 92656 USA (800) 713-4113, (949) 380-6100

Page 4

Rev. 0.1, 2013-10-23

Rev. 1.0, 2013-10-23

Basic Connection Instruction

Power Supply LOAD

Sub-20 USB-I2C Adaptor

SDA

AGND

SCL

Computer

Figure 2: Power Supply and Load Connection with I2C Implemented

Power Supply LOAD

Figure 3: Power Supply and Load Connection without I2C Implemented

LX7178 EVAL BOARD USER GUIDE

Microsemi

Analog Mixed Signal Group

One Enterprise Aliso Viejo, CA 92656 USA (800) 713-4113, (949) 380-6100

Page 5

Rev. 0.1, 2013-10-23

Rev. 1.0, 2013-10-23

LX7178 I2C GUI

Figure 4: LX7178 I2C GUI

LX7178 I2C GUI is a graphic user interface that can read/write IC status or change default

settings via I2C serial portal. For example, it can used to enable/disable device, change output

voltage, or enable power saving mode, etc.

More information about register map and I2C function can be found in LX7178 datasheet.

Note: To use this GUI, a sub-20 USB-I2C adaptor is needed. See Dimax SUB-20 Installation for

details.

LX7178 EVAL BOARD USER GUIDE

Microsemi

Analog Mixed Signal Group

One Enterprise Aliso Viejo, CA 92656 USA (800) 713-4113, (949) 380-6100

Page 6

Rev. 0.1, 2013-10-23

Rev. 1.0, 2013-10-23

Recommended Operating Conditions

Description

Symbol

Min

Max

Unit

Input Voltage

VIN

5.5

Output Current

IOUT

Operating Ambient Temperature

°C

Enable Chip

VIN

Shut Down Chip

Pull to GND

Enabling Regulator from I2C Bus

In addition to the EN pin, the regulator can be enabled and disabled via the I2C bus by

programming the control register. During disable, the regulator and most of the support circuitry

is turned off. However, the I2C bus circuitry is still active and maybe programmed.

Setting the Output Voltage

Using the I2C interface you can adjust VOUT from 0.6V to 1.2V. When I2C interface is

implemented, the reference voltage is programmed with the I2C bus VSEL register value.

    

Where NSEL is the decimal value of the 7 VSEL bits.

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

divider connected from SW to VOUT then to GND. For noise immunity, the lower resistor R2

from VOUT to GND should be greater than 100kΩ. The formula below calculates the value of

VOUT based on the resistor divider R1 & R2.

   



VREF is determined by the chip, for example, to set the LX7178-01CSP to a VOUT = 0.96V,

given VREF = 0.8V. First pick the lower resistor R2=150k, calculate the upper resistor R1=30.1k.

LX7178 EVAL BOARD USER GUIDE

Microsemi

Analog Mixed Signal Group

One Enterprise Aliso Viejo, CA 92656 USA (800) 713-4113, (949) 380-6100

Page 7

Rev. 0.1, 2013-10-23

Rev. 1.0, 2013-10-23

PCB Layout of Evaluation Board

The LX7178 EVAL Board is a 4-layer board, the thickness of the board is 63mil in total. The

second layer to top layer is 7mil, the third layer to the bottom layer is 7mil. No microvias or

blind vias are needed; each signal can leave the LX7178 directly without using any via under

the device. The layout so implemented can lower the ESL with the bypass capacitors C2, C3

and C9, only C4 is located some distance from the controller.

Figure 5: Layout Recommendation

LX7178 EVAL BOARD USER GUIDE

Microsemi

Analog Mixed Signal Group

One Enterprise Aliso Viejo, CA 92656 USA (800) 713-4113, (949) 380-6100

Page 8

Rev. 0.1, 2013-10-23

Rev. 1.0, 2013-10-23

Figure 6: Top Silkscreen

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