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Buck Converter

Characterization

Load Regulation & Efficiency

Objective

  1. Evaluate buck’s Vout stability across all load conditions

  2. Measure efficiency across all load conditions

Conditions

  1. Vin = 55V, 44.4V, 36V, 25.2V, 22.2V, 18V

  2. Iout from 0A to 4A with 50 data points (0.08A step)

  3. Set power supply slew rate to minimum

  4. Temperature: room

  5. Use 4-wire sensing on power supply

  6. Don’t use the same wire that goes to eload to measure Vout

Procedure

(scripting)

  1. Solder 1 pair of wires to eload, 1 wire at Vout

  2. Connect DMM to Vout

  3. Connect Power supply to Vin

  4. Turn on power supply

Load Transient

Line Regulation

Output Noise

Common Mode Noise

Inject noise on vbat+ and vbat- using a functional generator, observe buck vin waveform

Start-up behavior

Shut-down behavior

Safety Tests

Over Current

Short Circuit

Over voltage

input voltage surge

Turn on power supply and probe buck vin waveform using oscope, expecting some overshoot on the capture plot

Efuse

Characterization

Start-up

Shut-down

OCP

Short Circuit

PWM Buffer

Characterization

No buffer test

Inject PWM signal at 50% duty cycle at 50Hz

Buffer test

Inject Triangle signal range from 0V to 5V at 50Hz

Inject PWM signal at 50% duty cycle at 50Hz

20240626 Efuse Test:

Goal: Make sure efuses are soldered properly & Test efuses over current protection and short circuit protections

Pre-test preparation:

  1. Try to borrow an eload from Rover or Midnight Sun,

    1. if you can’t borrow the eload, make your own eload. Find the XT60 connector with around 10 resistors soldered together, it should have resistance labelled on it, around 1.67 ohm if I recall correctly. It is in a yellow connector organizer kit.

  2. Set up eload if you can borrow one

  3. Set up scope

    1. Vin channel

    2. Vout channel

    3. Iout channel, for this you need a current probe and it needs a 9V alkaline battery (Rockery has 9V battery if we don’t have any battery left)

  4. Lift R1 to disable buck

  5. Solder a wire at C15, connect power supply here to inject 6V

  6. For each efuse,

    1. Solder 2 wires at output, use one wire for load and another wire to measure Vout;

    2. Solder 1 wire at input to measure Vin

  7. Solder multiple ground wires

Test plan:

Check

  • No shorts caused by soldering rework on the PCB

  • Vout is 6V

  • Current Probe is working

Over Current Test

  1. Connect load

  2. Set Oscilloscope to Normal, trigger around 0.1 - 0.3A, we want to see the efuse retrying

  3. Turn on power supply

  4. Take a photo of Oscilloscope screen

  5. Repeat for all efuses

Short-to-ground Test

  1. Set Oscilloscope to Normal, trigger around 0.1 - 0.3A, we want to see the efuse retrying

  2. Turn on power supply

  3. use the load wire at efuse output, short it to any ground on the PCB (seeing spark is fine)

  4. Take a photo of Oscilloscope screen

  5. Repeat for all efuses

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