• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 63 subscribers
  • Views 278 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LMR70503 dummy load questions

Randy Wang
Intellectual 1705 points
Other Parts Discussed in Thread: LMR70503

Dear Team:

  My customer have some questions about LMR70503 dummy load, would you explain them to me, please?

1. Where the dummy load in the LMR70503 internal block?
2. How to setting the dummy load in the IC?
3. How to comfirm the dummy load is turn on or turn off base on the Vout waveform?

Thanks and Best Regards,

Randy Wang

  • 0
    TI__Genius 11085 points

    Randy,

    The dummy load is connected internally between Vout and Gnd via a small switch.

    The dummy load do not need setting or control or turning on/off. It is automatically turned on when Vout magnitude is higher than regulation. The turn on and off is smooth. The amount of current dummy load sinks is only depends on how much current needed to maintain Vout regulation. There is a curve in the datasheet showing the dummy load current vs Vfb offset. It is designed to only turn on when load is below 2 mA. The dummy load is on or off cannot be observed on the Vout waveform. The Vout ripple should be very small when load is almost zero.

    The purpose is to balance out the charging current when the LMR70503 is operating with min fs and min Ton and with almost no load. The sign of dummy load turning on is that the LMR70503 is operating with min switching frequency and min internal switch ON time, and the load is further reduced.

    Hope this helps understanding how the dummy load works.

    Yang Zhang - TI SVA Simple Switcher