Microsemi LX7180A User manual

LX7180A
User Guide
LX7180A 4 Amp Step-Down Converter Evaluation Board

LX7180A 4 Amp Step-Down Converter Evaluation Board
Microsemi Proprietary and Confidential. LX7180A User Guide Revision 1.0
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 Enabling Regulator from I²C Bus ......................................................................................................... 5
5.2 Setting the Output Voltage ................................................................................................................. 5
6 PCB Layout of Evaluation Board ..................................................................................................... 6
7 Bill of Materials ............................................................................................................................ 10
8 Efficiency Plot ............................................................................................................................... 11
9 Dynamic Load Response Scope Shots .......................................................................................... 12
10 Start-up and Short Condition Scope Shots ................................................................................. 15
11 Ordering Information .................................................................................................................. 17

LX7180A 4 Amp Step-Down Converter Evaluation Board
Microsemi Proprietary and Confidential. LX7180A User Guide Revision 1.0 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
This document was published in November 2017. It was the first publication of this document.

LX7180A 4 Amp Step-Down Converter Evaluation Board
Microsemi Proprietary and Confidential. LX7180A User Guide Revision 1.0 2
2 Product Description
The LX7180A is a 4 A step-down regulator with integrated MOSFETs packaged in a space-saving QFN12
2 mm × 2 mm for today’s mobile devices. It uses an ultra-fast, constant frequency hysteretic control
method to minimize external filter components while maintaining excellent regulation. The LX7180A
reference voltage is programmable from 0.6 V to 1.195 V through a high speed (up to 3.4 MHz), bi-
directional I C bus.
2
The LX7180A operates from 3 V to 5.5 V rails and outputs 0.6 V to 100% of the input voltage.
Cycle-by-cycle current limiting protects against over-current conditions. Hiccup mode provides
protection for heavy over-load or short-circuit faults. Thermal protection shuts down the regulator
under over-temperature conditions. Over voltage conditions will immediately shut off the output to
protect against permanent damage. The LX7180A automatically restarts when all fault conditions are
cleared.
2.1 Applications
High-performance HDDs
LCD TVs
Notebooks/netbooks
Servers and workstations
Video cards
PoE-powered devices
Smartphones
2.2 Key Features
0 A–4 A step-down regulator
Operational input supply voltage range: 3.0 V–5.5 V (short durations to 6.5 V)
Hysteretic control offers best transient response
PWM switching at a constant 1.65 MHz
Power save mode (PSM) can be selected to improve light load efficiency
100% duty ratio operation
Input under-voltage and over-voltage protection
Enable and Power Good function
I C serial interface at 3.4 Mbps
2
Internal soft-start
Cycle-by-cycle over current protection
Hiccup mode protects against short circuit faults
Seven-bit adjustable reference voltage through I C bus
2
RoHS-compliant

LX7180A 4 Amp Step-Down Converter Evaluation Board
Microsemi Proprietary and Confidential. LX7180A User Guide Revision 1.0 3
3 Evaluation Board Schematic
The following illustration shows the evaluation board schematic.
Figure 1 • Evaluation Board Schematic

LX7180A 4 Amp Step-Down Converter Evaluation Board
Microsemi Proprietary and Confidential. LX7180A User Guide Revision 1.0 4
4 Basic Connection Instructions
The following illustration shows how to connect the evaluation board to the power supply while I C is
2
implemented.
Figure 2 • Power Supply and Load Connection with I²C Implemented
The following illustration shows how to connect the board to the power supply without I C.
2
Figure 3 • Power Supply and Load Connection Without I²C Implemented

LX7180A 4 Amp Step-Down Converter Evaluation Board
Microsemi Proprietary and Confidential. LX7180A User Guide Revision 1.0 5
5 Recommended Operating Conditions
The following table lists the recommended operating characteristics for the LX7180A evaluation board.
Table 1 • Operating Conditions
Description Symbol Minimum Maximum Unit
Input voltage VIN 3.0 5.5 V
Output voltage VOUT 0.6 5.5 V
Output current (V = 3 V to 5 V)IN IOUT 0 4 A
Operating ambient temperature TA0 85 °C
Enable chip EN VIN
Shut down chip EN Pull to GND
5.1 Enabling Regulator from I²C Bus
In addition to the EN pin, the regulator can be enabled and disabled through the I C bus by
2
programming the control register. During disable, the regulator and most of the support circuitry is
turned off. However, the I C bus circuitry is still active and may be programmed.
2
5.2 Setting the Output Voltage
Using the I C interface, you can adjust V from 0.6 V to 1.2 V. When the I C interface is implemented,
2OUT 2
the reference voltage is programmed with the I C bus VSEL register value.
2
Where V 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 software to V then to GND.OUT
The following formula calculates the value of V based on the resistor divider R1 and R2.OUT
V is determined by the chip. For example, to set the LX7180A to a VOUT= 1.8 V, given V = 0.6 V, first REF REF
pick the lower resistor R2= 120K, calculate the upper resistor R1= 240K.

LX7180A 4 Amp Step-Down Converter Evaluation Board
Microsemi Proprietary and Confidential. LX7180A User Guide Revision 1.0 6
6 PCB Layout of Evaluation Board
The LX7180A evaluation board is a four-layer board. The recommended distance between ground layer
and the top layer is 6 mil. The following illustrations depict each of the board's four layers.
Figure 4 • Layer 1: Top

LX7180A 4 Amp Step-Down Converter Evaluation Board
Microsemi Proprietary and Confidential. LX7180A User Guide Revision 1.0 7
Figure 5 • Layer 2: Ground

LX7180A 4 Amp Step-Down Converter Evaluation Board
Microsemi Proprietary and Confidential. LX7180A User Guide Revision 1.0 8
Figure 6 • Layer 3: Sense