EVAL6482H

Posted on April 12, 2013 at 01:49

Update:

Changed CONFIG to 0x2F98 to raise VCC to 15V. Status is now 0xE703, so it looks like the  UVLO condition is gone, but I am still getting no motor steps. Please advise.

Posted on April 12, 2013 at 11:57

Hi,

the UVLO condition is due by the charge pump diodes mounted on the evaluation board. The voltage drop caused by BAV99 doesn't allow the board to operate @ VCC = 7.5V (VBOOT is below the UVLO threshold). 

If you need to operates at 7.5V you can replace the BAV99 with a low drop diode pair (eg the BAR43S).

Whe the device is in step-clock mode the internal logic considers the motor as stopped, so you can regulates the torque using the TVAL_HOLD register.

The OCD protection measures the Vds drop on the external MOSFETs, so the relation is current_limit [mA] x Rds(on) [ohm]

Posted on April 12, 2013 at 20:31

Hi Enrico,

Thank you for the clarification, but I am still unable to drive the motor. It looks like there is still some kind of error condition, since the FLAG LED is lit. However, the STATUS register is reported as 0xE603, indicating no errors. I tried to limit the number of commands sent to the board to only two (software reset and set CONFIG for 15V VCC), disconnected the motor from the board, and still no luck - FLAG LED is still lit, and the chip does not seem to ever exit the Hi-Z state. Is there application engineering support available on the USA West Coast?  Due to the time difference between us, it will take massive amounts of time to resolve this through the forum. Thank you!

Posted on April 16, 2013 at 16:29

This behavior is very strange. The FLAG output should not be forced low if no failure is present.

The device leaves the high impedance condition only when a motion command is received (e.g. hardstop), so it is ok if it is still in hiz after the GetStatus command.

Did you check the gate driver setup? The default configuration cannot drive the EVAL6482H MOSFETs.

The following setup should be OK:

Igate = 64 mA

tcc = 625 ns (no boost)

tdt = 250 ns

tblank = 500 ns

GATECFG1 = 0xC4

GATECFG = 0x61

Posted on April 16, 2013 at 17:09

I contacted our application support guy in US and he is glad to support you, but in this moment he have not access to the forum.

You can reach him by mail

Jean-Jacques MENEU

Mail: jean-jacques.meneu@st.com

Posted on April 17, 2013 at 00:48

Hi Enrico,

The gate driver settings you provided fixed the problem - thank you! The demo board is now fully functional and I can drive my stepper motor. It looks like gate driver settings are critical for proper chip operation - do you have any documentation (application note) that explains how to select proper gate driver settings for any other MOSFET? Also, thank you for providing Jean-Jacques contact information.

Caba

Posted on April 29, 2013 at 10:55

Hi Caba,

we are working on a specific AN.

In general the golden rules are the following:

1. the higher the IGATE, the faster is the output slew-rate (and related issues)

2. IGATE x TCC product should be at least equal to the total gate charge of the MOS

3. A dead-time of 250 ns fits most the applications

4. Blanking time must be adjusted according to the spurious signals generated by the MOSFET commutations on the SENSE pin (consider that the blanking starts AFTER the end of the commutation)

Ciao

Enrico