3
\$\begingroup\$

The 2nd line of the MAX14870 Function Table in its datasheet shows when PWM is low the outputs M1 and M2 are connected to GND and the Operating Mode is "Brake". My experience of DC motors indicates that there is a lot of drag when their terminals are shorted together so I agree that the motor will be braked under these conditions. I would expect PWM to alternatively power the motor through two quarters of the bridge in one direction or the other (set by the DIR pin) then allow it to freewheel with M1 and M2 at high impedance.
I have considered feeding EN with a PWM signal however there are significant turn-on and turn-off delays so that is not an option. I am left wondering how drivers like this work?

\$\endgroup\$
1
  • 1
    \$\begingroup\$ What happens if you remove the diode to GND in a buck convertor? \$\endgroup\$
    – user16324
    Jun 29, 2021 at 11:28

1 Answer 1

2
\$\begingroup\$

There are two devices in the data sheet: -

The MAX14870's main application is for PWM control of a DC motor and, under these circumstances, the lower MOSFETs are used as a synchronous diode as per any synchronous switching regulator.

The MAX14872's main application is as a DC motor controller and, instead of taking a PWM input, it uses a forward/reverse control input. For this device, the truth table shows that it can be used in free-wheel mode (no braking): -

enter image description here

And, it can also be used to brake, depending how you drive the FWD and REV pins. If you bought the wrong one then I suggest you buy the other and take care reading the data sheet.

\$\endgroup\$
3
  • \$\begingroup\$ Thank you @andy-aka for your answer. I interpret it to imply that the MAX14870 should be used to control the current through a DC motor which would make it suitable for torque control, such as a tensioner system. Whereas I am wanting to control speed (and position in the bigger picture). Hence the MAX14872 is more suitable. Is that in fact the case? \$\endgroup\$
    – Ken Mercer
    Jun 30, 2021 at 21:30
  • \$\begingroup\$ @KenMercer I'm not making a recommendation; I'm only pointing out that you can use the 14872 in free-run mode because that appears to be what it is designed for. I'm also recommending that you read the data sheet to double-check everything. There is neither enough room nor time nor site-allowance to permit a full analysis of your requirements. This is a Q and A site and not a product recommendation site. Here are some rules and guidelines: electronics.stackexchange.com/help/on-topic - they can be found by clicking on the top right "?" icon. \$\endgroup\$
    – Andy aka
    Jul 1, 2021 at 7:06
  • \$\begingroup\$ Fair point - this is morphing into a different question. I'm accepting your answer. \$\endgroup\$
    – Ken Mercer
    Jul 1, 2021 at 23:42

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.