SNVU918 October   2024 LM68645-Q1

 

  1.   1
  2.   Description
  3.   Features
  4.   4
  5. 1Evaluation Module Overview
    1. 1.1 Introduction
    2. 1.2 Kit Contents
    3. 1.3 Specification
    4. 1.4 Device Information
  6. 2Hardware
    1. 2.1 Additional Images
    2. 2.2 Power Requirements
    3. 2.3 Setup and Operation
  7. 3Implementation Results
    1. 3.1 Evaluation Setup
    2. 3.2 Performance Data and Results
  8. 4Hardware Design Files
    1. 4.1 Schematics
    2. 4.2 PCB Layouts
    3. 4.3 Bill of Materials (BOM)
  9. 5Additional Information
    1. 5.1 Trademarks

2.3 Setup and Operation

This section describes the connectors, test points, and jumpers on the EVM and how to properly connect, set up, and use the LM68645EVM. For location of connectors and jumpers and typical setup, see Figure 2-3.

    VOUTOutput voltage of the converter.VOUT banana post. Apply load to this connector.
    VOUTSThe VOUTS test point is used to monitor output voltage.
    GNDSTest point next to VOUTS test point.This GNDS test point is used as the negative DMM connection for VOUT sensing.
    VINInput voltage to the converter.VIN banana post. Apply input voltage to this connector.
    VINSThe VINS test point is used to monitor input voltage.
    GNDSTest point next to VINS test point.This GNDS test point is used as the negative DMM connection for VIN sensing.
    GNDGround of the converter.GND banana posts. Apply load ground and input voltage ground to these connectors.
    ENThe use of the EN jumper is self-explanatory. To supply an external signal to the EN input of the device, remove the EN jumper shunt and apply the signal to the EN test point.To use the external UVLO feature, populate Rent (R3) and Renb (R4) as desired and remove the EN jumper shunt. Note that for accurate shutdown current measurement, these resistors must be removed (if used) and the EN jumper shunt moved to OFF.
    RTThe RT jumper is used to select the switching frequency and is self explanatory.The default inductor on the EVM is designed for 400kHz operation. Other frequencies require a different value of inductance.To adjust the switching frequency, remove the RT jumper shunt and populate RT (R5) with the desired value. See the LM686x5 data sheet for frequency vs. RT resistor value.
    Feed-back ConnectionsThe EVM is set for a fixed 5V output, with Rfbt2 (R6), 0Ω, populated. To set the output voltage to 3.3V, remove Rfbt2 (R6) and populate Rfbb (R9) with a 0Ω resistor. Note that Rsnsh (R14) is populated with a 4.99kΩ resistor.To use the adjustable output voltage mode (ADJ), populate Rfbt (R8) and Rfbb (R9) with the appropriate value resistors. Rinj (R7) must also be populated with a 10Ω to 50Ω resistor. The reference voltage is 0.8V. See the LM686x5 data sheet for appropriate values of feed-back resistors.When using the adjustable output voltage mode, a Bode plot can be taken using the Rinj (R7) resistor. This resistor becomes the injection point for the frequency response analyzer, allowing the loop frequency response to be taken in the usual way. In the fixed output voltage mode, a loop response can not be taken. In ADJ mode, an auxiliary voltage divider is needed between the output voltage node and the VSNS pin of the regulator. This divider is provided by Rsnsh (R14) and RsnsL (R15). The values and ratio of this auxiliary divider must be the same as those of the main feed-back divider.
    PGOODThe PGOOD test point is used to monitor the power-good indicator. This flag indicates whether the output voltage has reached the regulation level. PGOOD is an open-drain output that is tied to VOUT through a 100kΩ, resistor Rpg (R1).
    VCCVCC test pointThe VCC pin is the output of the internal LDO. The LDO voltage is typically 3.3V. This point can be used for logic input and/or logic pull-ups. Do not connect to external loads.
    BIASAuxiliary input to LDO regulatorConnected to VOUT through Rbias (R10) on EVM. To change the input supply of the LDO, remove Rbias (R10) and connect external input to BIAS pin, or ground BIAS pin as required. Populate Cbias (C11) with a 0.1μF capacitor when using external supply to BIAS pin. See LM686x5 data sheet for more information.
    FAULT The FAULT test point is used to monitor if any fault has occurred in the regulator or the system. This is a low going signal, with a low indicating a fault. The pin is pulled up to VIN by Rflt (R12) through a 100kΩ resistor.
    Bode PlotWhen using the adjustable output voltage mode, a Bode plot can be taken using the connection shown in Figure 2-4. Rinj (R7) must be populated for this test.
    EMI FilterThe EMI filter is not populated on this EVM. To evaluate the EMI filter, components L2, C1-C2, C19-C20 must be populated, while R11 must be removed. Typical values for these components are given in Table 4-1.
LM68645EVM LM68645EVM Setup Figure 2-3 LM68645EVM Setup
LM68645EVM LM68645EVM Loop Response Connections Figure 2-4 LM68645EVM Loop Response Connections