Microsemi LX7175 Manual de usuario
LX7175
User Guide
LX7175 3 Amp Step-Down Converter Evaluation Board
LX7175 3 Amp Step-Down Converter Evaluation Board
LX7175 User Guide Revision 2.0
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 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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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)
LX7175 3 Amp Step-Down Converter Evaluation Board
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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 User Guide Revision 2.0 5
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
LX7175 3 Amp Step-Down Converter Evaluation Board
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Figure 5 • Layer 2: Inner Layer 1
Tabla de contenidos
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