Microsemi LX7178 User Manual

LX7178 EVAL BOARD USER GUIDE

Copyright  2012
Rev. 0.1, 2013-10-23

LX7178 5 Amp Step Down Converter

LX7178 EVALUATION BOARD

USER GUIDE

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Microsemi

Analog Mixed Signal Group

LX7178 EVAL BOARD USER GUIDE

Copyright  2012
Rev. 0.1, 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

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LX7178 EVAL BOARD USER GUIDE

Page 1

Copyright  2012
Rev. 0.1, 2013-10-23

Introduction to Product

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

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LX7178 EVAL BOARD USER GUIDE

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Key Features

 Constant Frequency Hysteretic Control
 Extremely Fast Line/Load Transient Response
 I2C for Output Adjustment (3.4Mbps)
 1.875MHz Switching Frequency
 Extremely Low-R
 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

MOSFETS

DSON

Applications

 High Performance HDD
 Notebook/ Netbook
 Tablets/ Slates

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LX7178 EVAL BOARD USER GUIDE

Page 3

Copyright  2012
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IC Part Number

Description

LX7178-xyCSP

WLCSP 20Ball 0.4mm Pitch

Evaluation Board Part Number

Description

LX7178 EVAL BOARD

Evaluation PCB for LX7178

Part Specific Information

Note: “x” is the 2 LSB bits of the binary I

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

2

C slave address (0 to 3);

Evaluation Board Schematic

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Figure 1: Schematic of Evaluation Board

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Analog Mixed Signal Group

LX7178 EVAL BOARD USER GUIDE

Page 4

Copyright  2012
Rev. 0.1, 2013-10-23

Power Supply

LOAD

Sub-20 USB-I2C Adaptor

IN

SDA

AGND

SCL

Computer

Power Supply

LOAD

Basic Connection Instruction

Figure 2: Power Supply and Load Connection with I2C Implemented

Figure 3: Power Supply and Load Connection without I2C Implemented

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LX7178 EVAL BOARD USER GUIDE

Page 5

Copyright  2012
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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.

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Description

Symbol

Min

Max

Unit

Input Voltage

VIN

3

5.5 V Output Current

I

OUT

5 A

Operating Ambient Temperature

TA 0 85

°C

Enable Chip

EN

VIN

Shut Down Chip

EN Pull to GND

Recommended Operating Conditions

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 N

  



is the decimal value of the 7 VSEL bits.

SEL





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.



  

V

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

REF

given V

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

REF



 





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Analog Mixed Signal Group

LX7178 EVAL BOARD USER GUIDE

Page 7

Copyright  2012
Rev. 0.1, 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

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Copyright  2012
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Figure 6: Top Silkscreen

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LX7178 EVAL BOARD USER GUIDE

Page 9

Copyright  2012
Rev. 0.1, 2013-10-23

Figure 7: Layer 1: Top Layer

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Figure 8: Layer 2: Ground Layer

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LX7178 EVAL BOARD USER GUIDE

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Copyright  2012
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Figure 9: Layer 3: Sense Layer

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Figure 10: Layer 4: Bottom Layer

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LX7178 EVAL BOARD USER GUIDE

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Copyright  2012
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MISCELLANEOUS COMPONENTS

Item

Part Description

Reference

Qty

1

Microsemi IC – LX7178-xy

U1

1

2

Test Point

SW, PGOOD, VIN_S, VO_S,
GND_S, GND_S

6
3

Terminal

VIN, VOUT, GND, GND

4 4 Jumper/3pin

JP2

1 5 Jumper/4pin

J2

1

CAPACITORS

Item

Part Description

Reference

Qty

6

1uF/10V/X5R

C2 1 7

22uF/10V/X5R

C3, C8

2 8 47uF Electronic/35V

C4 1 9

22uF/6.3V/X5R

C5, C6, C7

3

RESISTORS

Item

Part Description

Reference

Qty

10

30.1kΩ

R1

1

11

150kΩ

R3 1 12

10kΩ

R5, R6

2

13

100kΩ

R7 1 14 0 R8

INDUCTOR

Item

Part Description

Reference

Qty

15

0.47uH -- IHLP-2020CZ-01series

L1

1

Bill of Material

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LX7178 EVAL BOARD USER GUIDE

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Copyright  2012
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0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

10 100 1000

Efficiency

Load Current (mA)

LX7178 5V VIN Efficiency

0.96V PSM

0.96V PWM

1.8V PSM

1.8V PWM

3.3V PSM

3.3V PWM

+

Efficiency Plot

Figure 11: Efficiency Plot of LX7178-01CSP

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Figure 12: No load to 0.5A PWM

Figure 13: No load to 0.5A PSM

CH2: VOUT, CH4: I

LOAD

CH2: VOUT, CH4: I

LOAD

Figure 14: 0.5A to 2.5A PWM

CH2: VOUT, CH4: I

LOAD

Figure 15: 0.8A to 2.5A PWM

CH2: VOUT, CH4: I

LOAD

Dynamic Load Response Scope Shots

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Figure 16: 0.5A to 2.5A PWM Rising Edge

Figure 17: No load to 0.5A PSM Rising Edge

CH2: VOUT, CH3: SW, CH4: I

LOAD

CH2: VOUT, CH3: SW, CH4: I

LOAD

Figure 18: 0.5A to 2.5A PWM Falling Edge

CH2: VOUT, CH3: SW, CH4: I

LOAD

Figure 19: No load to 0.5A PSM Falling Edge

CH2: VOUT, CH3: SW, CH4: I

LOAD

Dynamic Load Response Scope Shots (Continue)

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Figure 20: Startup with ENABLE toggled

Figure 21: Soft start VIN tied to ENABLE

CH2: EN, CH3: VOUT

CH2: EN, CH3: VOUT

Figure 22: Start Up When Vin=4.5V Load=0.5ohm

CH2: PG, CH3: VOUT, CH4: Inductor Current

Figure 23: Power into Short

CH2: VIN, CH3: VOUT, CH4: Inductor Current

Start up and Short Condition Scope Shots

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Figure 24: Power after Short

Figure 25: Recovery from Short

CH2: VIN, CH3: VOUT, CH4: Inductor Current

CH2: VIN, CH3: VOUT, CH4: Inductor Current

Start up and Short Condition Scope Shots
(Continue)

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Copyright  2012
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Dimax Sub20 Installation

Figure 19 Dimax SUB-20 Adapter

1. Uninstall any previous version of the SUB-20 adapter if exist.

2. Download and install SUB-20 USB driver from

http://www.xdimax.net/download/SUB-20-120121-x32.exe

Note: Install the x64 driver file for 64-bit systems.

More downloads available at http://www.xdimax.com/sub20/sub20.html#DLD

3. Connect SUB-20 device to computer's USB,

If this is the first time you connect the specific device, wait for SUB-20 driver installation
to finish - Found new hardware, let computer auto search for driver.

4. Firmware update:

 The SUB-20 firmware version should be 0.3.5.
 Open “Firmware updater” tool. The Firmware updater tool has a shortcut on the

desktop. It may also be found at Start Programs  SUB-20  Firmware
updater.

5. Follow the instructions in the following link: SUB-20 Firmware Update

6. Connect the adaptor according to the following connection:

 4 PIN to 9PIN cable connects LX7178 EVB I2C port and SUB-20 ( Unused pin

on 4 PIN connecter aligns with V+ pin on I2C port )

 USB to mini-USB cable connects SUB-20 and PC
 SUB-20 DB-9 connector pin #5 = GND
 SUB-20 DB-9 connector pin #6 = I2C_SDA
 SUB-20 DB-9 connector pin #8 = I2C_SCL

7. Install LX7178 GUI

Click CD:/LX7178 GUI/I2C Register Access_1_0_8_x.exe to start the installation,
To open the GUI, go to Startup> All Programs> Microsemi> Register Access>
Choose "LX7165" when "production selects window “pops out.

8. LX7178 GUI and SUB-20 driver could be found in the Support CD

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