• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 31 subscribers
  • Views 205 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.

DRV8353: DRV8353: using external amplifier to overcurrent protection

SungDong Kim
Prodigy 10 points

Part Number: DRV8353

image.png

Hello,
I am designing a 3-phase BLDC motor controller using the DRV8353. I want to implement a custom overcurrent protection (OCP) using an external non-inverting amplifier, but I am concerned about the DRV8353 operation.
[The Setup]
Shunt Configuration: I want to use a fixed-value shunt resistor between the Low-side MOSFET Source and GND.

Current Sensing: The voltage across the shunt is fed into an external non-inverting amplifier because the raw shunt voltage at my target current(set to overcurrent) is too low for the OCP response. [For example, the shunt resistor is 0.1ohm and overcurrent is 2A. And then, the voltage at the shunt resistor is 0.2V. But if the OCP voltage is 0.5V, OCP will not work. So I want to use amplifier to boost 0.2V to 0.5V.] 


[The Core Question]
If I use an external amplifier in this way, the voltage potential at the SPx (and consequently the low-side internal Gate Driver Source in the DRV8353) will differ from the actual physical Source voltage of the low-side external MOSFETs.

Potential Mismatch: If there is a voltage difference (e.g., 0.1V ~ 0.3V) between the actual MOSFET Source and the SPx pin due to the external amplifier, will this cause instability of the gate drive stage?

Allowable Range: Is there a maximum allowable voltage offset between the actual MOSFET Source and the SPx reference before gate drive performance degrades or the device is damaged?

 

 

 

 

 

  • 0
    TI__Genius 13275 points

    Hello,

    I don't think the slight offset would cause an issue with the DRV device SP-SN pins. 

    If you are using an external amp to provide current sense, you can disable the DRV device's OCP and rely solely on your external protection.

    Thanks!

    Joseph

  • 0 in reply to Joseph Ferri
    Prodigy 10 points

    Hi,

    Can I use a non-inverting amplifier between the shunt resistor and the SPC pin to enable the DRV device's OCP without changing the shunt resistor value?

    Thanks!

  • 0 in reply to SungDong Kim
    TI__Genius 13275 points

    Hello,

    Yes, but you would need to be aware that the device's OCP trigger levels would be different, making sure that this would not trigger during regular operation. I'm not sure what this would do in regards to the voltage level seen on the SP pin. As long as it does not violate any abs max specs, and does not trigger 'falsely' you should be good.

    Thanks,

    Joseph