0
\$\begingroup\$

MIC4605-2YM Datasheet

Given the circuit above what is the proper way to drive this H bridge in a manner where I can change the motor direction. the datasheet shows a sample circuit of a full H bridge driver scheme, however it uses a version of the half bridge driver that accepts 2 different PWM signals. The version that I have accepts one signal and it handles the inversion.

Do i necessarily need a second driver in this case? Cant I just pull up the top right mosfet and pull down the lower right mosfet and then ill get my direction change. Obviously adding some dead time.

Or do I need a second half bridge driver of the same configuration? In that case at 50% duty cycle which way will it spin?

\$\endgroup\$
3
  • \$\begingroup\$ No, your idea will not work at all - you do in fact need two drivers. \$\endgroup\$ Commented Apr 8, 2019 at 4:20
  • \$\begingroup\$ You must specify motor datasheet and purpose . PWM speed and direction? \$\endgroup\$ Commented Apr 8, 2019 at 6:43
  • \$\begingroup\$ How do you bootstap the top side driver? \$\endgroup\$
    – winny
    Commented Apr 8, 2019 at 8:10

1 Answer 1

1
\$\begingroup\$

Do i necessarily need a second driver in this case? Cant I just pull up the top right mosfet and pull down the lower right mosfet and then ill get my direction change. Obviously adding some dead time.

You can, but how are you going to do that? The top mosfet needs more more voltage than the supply (VDD) provides on its gate.

Or do I need a second half bridge driver of the same configuration? In that case at 50% duty cycle which way will it spin?

This is the easiest way: Put a second half bridge driver on the other side and use a different PWM signal to command reverse rotation.

PWM1 commands forwards rotation, PWM2 commands reverse rotation, only turn one on at a time. you could use a logic circuit if your micro-controller only has a single PWM output available to command the motor.

schematic

simulate this circuit – Schematic created using CircuitLab NAND2 is just being an inverter, but if you like DIP parts, you can only buy NANDs in packs of 4

You could drive the seconds H bridge from an inverted version of the first PWM, but that may prove wasteful of energy when a stop (50% PWM) or low speed is commanded. also it may be hard to get the exact right PWM to cause a stop.

\$\endgroup\$
8
  • \$\begingroup\$ Yes that is true I forgot I need that high side N channel fet to be a higher voltage thus the driver IC in the first place. When you say to only turn on one at a time would I need some additional circuitry ? Because If only turn on the Left driver for example then both my right side fets will be off and obviously I need one of them on. \$\endgroup\$ Commented Apr 8, 2019 at 5:12
  • 1
    \$\begingroup\$ So maybe just put the IC into 100% duty cycle? or 0% duty.... same thing since at 100% duty cycle one fet will be off and the other will on and if I do 0% duty cycle still one fet is on and the other is off just opposite of the 100% duty. I think preferably the fet the low fet should be fully on since the bootstrap requires switching to not drain the cap. \$\endgroup\$ Commented Apr 8, 2019 at 5:12
  • \$\begingroup\$ I hope it is clear from the picture that driver drives both fets in a complementary fashion which I chose for convenience but I think it also complicates things because I dont have the ability to just turn on fet off and drive the other. maybe I will go with the version of this IC that does let me control each fet with its own PWM and just have the microcontroller generate the required PWM signals and deadtime etc... \$\endgroup\$ Commented Apr 8, 2019 at 5:15
  • \$\begingroup\$ yes, just put a high signal into the one you don't want. that should turn the bottom MOSFET on. \$\endgroup\$ Commented Apr 8, 2019 at 5:15
  • \$\begingroup\$ The opening of this is mistaken - forget about meeting the gate drive requirements or not, permanently wiring the FET gates is at best equivalent to replacing the FET's with closed or open wires - which is to say, at most unidirectional control. \$\endgroup\$ Commented Apr 8, 2019 at 5:23

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.