Microsemi LX7178 User manual

LX7178 EVAL BOARD USER GUIDE
Microsemi
Analog Mixed Signal Group
One Enterprise Aliso Viejo, CA 92656 USA [phone], [phone]
Copyright 2012
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 [phone], [phone]
Copyright 2012
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 [phone], [phone]
Page 1
Copyright 2012
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 [phone], [phone]
Page 2
Copyright 2012
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 [phone], [phone]
Page 3
Copyright 2012
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 [phone], [phone]
Page 4
Copyright 2012
Rev. 0.1, 2013-10-23
Rev. 1.0, 2013-10-23
Basic Connection Instruction
Power Supply LOAD
Sub-20 USB-I2C Adaptor
IN
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 [phone], [phone]
Page 5
Copyright 2012
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 [phone], [phone]
Page 6
Copyright 2012
Rev. 0.1, 2013-10-23
Rev. 1.0, 2013-10-23
Recommended Operating Conditions
Description
Symbol
Min
Max
Unit
Input Voltage
VIN
3
5.5
V
Output Current
IOUT
5
A
Operating Ambient Temperature
TA
0
85
°C
Enable Chip
EN
VIN
Shut Down Chip
EN
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 [phone], [phone]
Page 7
Copyright 2012
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 [phone], [phone]
Page 8
Copyright 2012
Rev. 0.1, 2013-10-23
Rev. 1.0, 2013-10-23
Figure 6: Top Silkscreen