• State
  • Locked Locked
  • Replies 4 replies
  • Subscribers 63 subscribers
  • Views 479 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.

LM5155: Compensation loop for constant current solenoid driver application

i huff magic smoke
Prodigy 10 points
Part Number: LM5155
Other Parts Discussed in Thread: DRV110

Hi, 

Trying to implement a solenoid driver and confused about the approach to choosing loop compensation for constant current driver (basically identical use case as for DRV110/120)



I've read that type2 comp is usually chosen from ESR*cap of output electrolytics, but in this case there is no output capacitance since im just pulling current thru a solenoid. 

Switching at 100kHz, i have 20V/V current sense amp acorss the 33mOhm sense resistor). 


Can you offer any guidance for this?

  • 0
    TI__Genius 15855 points

    Hi,

    Thanks for using the E2E forum.

    I am sorry, i dont unterstand how your circuit should work. Can you please explain why is CS connected to GND? 

    Where is the Feedback coming from?

    In a switching regulator you will need an output capacitance.Even it is a constant current driver. Otherwise you will not be able to regulate.

    When you only want to turn a MOSFET on and off, there is no need to regulate and with that no need for a compensation.

    Best regards,

    Moritz

  • 0 in reply to Moritz
    Prodigy 10 points
    Moritz said:

    I am sorry, i dont unterstand how your circuit should work. Can you please explain why is CS connected to GND? 

    very similar to a buck converter, Except instead of using voltage divider I am only regulating current. 

    Moritz said:

    Where is the Feedback coming from?


    for the feedback its the current sense amp, basically all its doing is providing gain for hte sense resistor so 150mOhm i want to gain it by 6.66V/V so i can. 

    During off cycle the current is going thru the freewheel diode. 

    Moritz said:
    In a switching regulator you will need an output capacitance.Even it is a constant current driver.

    Why would i need it for solenoid driver and where would i put it. 


  • 0 in reply to i huff magic smoke
    TI__Genius 15855 points

    Hi ,

    Thanks, with the full schematic its clear now.

    I would recommend to connect the output of you amplifier circuit directly to comp-pin. The feedback has to be connected to ground in this case. The compensation is then done in your amplifier circuit.

    If you want to keep the connection to FB, it might be that a type 1 compensation at Comp is enough. You would have to try this.

    Best regards,

    Moritz

  • 0 in reply to Moritz
    Prodigy 10 points


    bruh noooo

    Moritz said:
    I would recommend to connect the output of you amplifier circuit directly to comp-pin