2013-04-11 02:08 PM
I am trying to use the evaluation board for the L6482 driver chip in StepClock mode, but I have been unable to move the motor. The status word is reported as 0xE503, indicating an UVLO condition. A second read of the status register returns the same value, indicating the condition is persistent and not power-up reset related.
CONFIG word is set to 0x2C98, and the board voltages are as follows: VS=24.28V VCC=7.52V VREG=3.37V VDD=5.03V (supplied from an external microcontroller board) VBOOT=30.24V Question #2: What TVAL register controls the motor current in StepClock mode? Is it TVAL_RUN? Question #3: How are OCD_TH settings in [mV] related to the actual current limit in mA? Is it OCD_TH [mV] = current_limit [mA] x Rsense [ohm]?2013-04-11 04:49 PM
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.2013-04-12 02:57 AM
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]2013-04-12 11:31 AM
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!2013-04-16 07:29 AM
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 = 0x612013-04-16 08:09 AM
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 mailJean-Jacques MENEUMail: jean-jacques.meneu@st.com2013-04-16 03:48 PM
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. Caba2013-04-29 01:55 AM
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 MOS3. A dead-time of 250 ns fits most the applications4. 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)CiaoEnrico