DRV8426E: DRV8426E/P max current IOCP and IREG

Hello Sylvain,

Thanks for your interest in the DRV8426P! In general there are a couple key differences between IOCP and IREG, more information in this FAQ post: 

• triggering OCP will disable all H-bridge FETs, fault condition reported
• triggering current regulation instead results in H-bridge current decay

To answer your question, since IREG is adjustable due to VREFx being adjustable, the absolute maximum voltage value on VREFx is 5.75 V. Assuming KV is the nominal 2.2 V/A value and IOCP is the minimum 2.5 A value, this is a condition in which IOCP is triggered:

• IREG = VREFx / KV = 5.75 V / 2.2 V/A = 2.61 A
• IOCP = 2.5 A

Hello,

I will calculate Vref to ensure that IREG is a bit lower than IOCP in all cases (KV variation)

With VRef =5V:

•  IREG min = 5/ 2.31= 2.16A
•  IREG min = 5/ 2.09= 2.39A

With VREF=5V, I make sure that IOC will never be triggered under normal conditions.

Is it OK for you?

What is the risk/consequence if VREFx is outside the  "Recommaned Operating conditions" (0.05V -3.3V)?

Best Regards.

Sylvain

Hello Sylvain,

It is not advisable to operate outside of the Recommended Operating Conditions given in the datasheet. Operating the device outside of Recommended Operating Conditions but within Absolute Maximum Ratings can result in device performance outside of the specifications given by the datasheet. Device operation outside of Absolute Maximum Ratings can damage the device. There is a footnote in the datasheet (copied and pasted below) that states:

"Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended Operating Conditions. Exposure to absolute-maximum rated conditions for extended periods may affect device reliability."

Thanks!

Tilden

Hello Tilden,

Thank you for your explanation. I have already read the application notes that discuss the recommended operating conditions and that's why I asked you the question.

On the one hand, you wrote that IREG can be 2.6A if VREFx=5.5V and on the other hand, I noticed that this VREF value is outside the recommended operating conditions.

If you have a DC motor with a peak current of 2A, it is not possible to adjust VREF within the "recommended operating conditions" so I don't understand why the datasheet mentions "2.5-A peak (brushed)".

Is there a trick to doing this or should I use another part (DRV8424P for example).

Thanks you

Sylvain,

Even if current regulation point is below Iocp level, then Iocp can still occur.  Iocp is meant to protect against direct shorts on the outputs to GND/VM/or other output.  

The "peak" number in the datasheet is based off this Iocp limitation.  That is all.

What are the needs of the customer exactly?  How much current do they need and do they want current regulation or not?

Regards,

Ryan

Hi Ryan,

My needs are to drive a brushed DC motor with the following specifications:

- Power supply :16V

- Current at maximum efficiency 0.5A

- No load current 0.15

- Stall current: 2.1A

- The maximum torque of the motor at start up must be kept.

As I have to keep the maximum torque, I must not limit the current below 2.1A.

Best Regards.

Sylvain