SNVU621D May   2019  – July 2021 LM61440 , LM61440-Q1 , LM61460 , LM61460-Q1

 

  1.   Trademarks
  2. 1Introduction
    1. 1.1 LM61460 Synchronous Step-Down Voltage Converter
    2. 1.2 LM61460-Q1 Evaluation Module
  3. 2Quick Start
  4. 3Detailed Descriptions
  5. 4Schematic
    1. 4.1 Alternative BOM Configurations
  6. 5Board Layout
  7. 6LM61460EVM Board Test Results
    1. 6.1 EMI
    2. 6.2 Board Efficiency
    3. 6.3 Load Regulation
  8. 7Bill of Materials
  9. 8Revision History

3 Detailed Descriptions

This section describes the connectors on the EVM and how to properly connect, set up, and use the EVM. See Figure 2-1 for a top view of the EVM.

    VOUTOutput voltage of the converter

    VOUT connectors connect to the power inductor and output capacitors. Connect the load between VOUT connector and the GND connector right next to it to provide load current. Connect the loading device to the board with short and thick wires to handle the large DC output current.

    GNDGround of the converter

    The GND is connected to the PGND and AGND pins of the device, as well as the ground of the input and output capacitors. The GND connections next to VIN, VIN_EMI, and VOUT connectors are meant for current return path for the supply voltage and load, respectively. Connectors are provided in pairs to allow easy and accurate sensing of voltages. Connect to supply and load grounds with short and thick wires. Other GND connectors are for signal measurement and probing.

    VINInput voltage to the converter

    The VIN connector connects to the input capacitors and the VIN pins of the LM61460-Q1. Connect the supply voltage from a power supply or a battery between VIN and GND connectors as power input to the device. The voltage range must be higher than 3.9 V for the device to start up. VIN higher than 6 V provides regulated 5 V output voltage. VIN must be no higher than 36 V to avoid damaging the device. After start-up, the device stays active until VIN drops below 3 V. The current limit on the supply must be high enough to provide the needed supply current. Otherwise, the supply voltage does not maintain the desired voltage. The supply voltage must be connected to the board with short and thick wires to handle the pulsing input current. If long cables are used to power up the board, damping must be provided by added CFLT3 and RFLT3 to avoid oscillation between the cable parasitic inductance and the low-ESR ceramic capacitors.

    VIN_EMIInput voltage to input filter of the converter

    If the input filter is desired between the supply and the LM61460-Q1, connect the supply voltage between VIN_EMI and GND_EMI. The supply voltage must be connected to the board with short and thick wires to handle pulsing input current.

    The input filter consists of the following: CF1, CF2, CF3, CF4, CF5, CF6, and L2. CD1, CD2, RD1, and RD2 are provided to allow more options to during filter design. To include the input filter in the power path, connect the supply voltage between the VIN_EMI and GND_EMI connectors. The output of the filter is connected to VIN, which is connected to the VIN pins of the LM61460-Q1 and the input capacitors.

    Conducted EMI arises from the normal operation of switching circuits. The ON and OFF actions of the power switches generate large discontinuous currents. The discontinuous currents are present at the input side of buck converters. Voltage ripple generated by discontinuous currents can be conducted to the voltage supply for the buck converter. Without filtering, excessive input voltage ripple can compromise operation of other circuits connected to this source. The input filter helps smooth out the voltage perturbations leading to less noise at the power source.

    GND_EMIGround return for the input filter

    This is the current return path for the supply connected to VIN_EMI. It provides a short-loop connection to the input filter capacitors to best filter the conducted noise generated from the PCB. Use VIN_EMI and GND_EMI connection if input filter is used and conducted EMI test is desired.

    CLKFor synchronization clock input

    The CLK input connector is designed for external clock input to the EN/SYNC pin. Switching action of the buck is synchronized to the external clock when it is present. The operation mode changes to forced PWM mode automatically, maintaining a constant switching frequency at light load.

    ENTo monitor the EN pin or input EN control signal

    This test point is used to monitor the voltage on the device EN pin. By default, the EN pin is connected to the mid-point of an enable divider. Note that the lower resistor in this divider, RENB, is not populated.

    PGTo monitor the PGOOD/RESET pin

    The PGOOD flag indicates whether the output voltage is within the regulation band. The PGOOD pin of the device is an open-drain output and it is pulled up to VOUT on this board through a pullup resistor. This flag is high impedance when the output voltage is in regulation.

    VinjTo aid when making bode plots

    There is a low value resistor, Rinj, between VOUT and this node. This feedback divider of the board is connected to this node as well. Stimulus can be applied between this node and VOUT when taking measurements for bode plots.

    VOUTSKelvin sensing for VOUT

    This connector is provided to allow VOUT to be measured more accurately.

    VINSKelvin sensing for VIN

    This connector is provided to allow VIN to be measured more accurately.