How to configure POWERSTEP01 ocd_th in current mode?

[BL1]

Hi,

Using IHM03A1, I try to drive a 48V-9A motor.

I've set up the POWERSTEP01 driver in current mode, with default registers values, which works nicely but with low torque. Now I want to increase current up to 9A.

I've changed IHM03A1 R1 and R2 resistances to 15mOhm+-1% / 3W ones.

According to current mode , I've set ALARM_EN to 0x8F ( disable ADC UVLO, disable stall detection, disable switch).

Last thing to do is to increase OCD_TH to enable 9A . But OCD_TH is set in Volt, which resistance value should I use for the convertion.

Thanks

[Cristiana SCARAMEL · Accepted solution]

Hello @BL​,

the powerSTEP01 measures the load current of each phase sensing the VDS voltage of the all integrated MOSFETs.

You can estimate the drop on the MOS using the Rdson typical value at 125 °C (23 mohm).

For the high side MOSFETs --> Vocd = 23 mOhm x 9 A = 207 mV

For the low side you have to calculate the threshold taking into account also the drop on the sense resistor.

Vocd = (23 + 13 ) mOhm x 9 A = 324 mV

In general, when you set the OCD threshold you should taking into account of the Rdson variation in temperature.

Moreover lower threshold is more sensitive to a noise.

[BL1]

Hello @Cristiana SCARAMEL​ ,

Thanks

As I don't want to be noise sensitive, so if I well understood, I should set OCD_TH to 324mV.

But as I don't want overcurrent detection to trigger for notiong, do you recommand to set it a little higher? With OCD_TH = 324mV , every time current will be a little higher 9A, overcurrent flag will trigger, or is there already a tolerance?

[Cristiana SCARAMEL]

Hello @BL​,

in your case you can round up to the typical value 343.75 mV (OCD_TH = '1010').

As reported in the datasheet (Table 4 pg 15), the OCD voltage threshold is equal at typical value ±10%