Additional gate drivers for TMC262 with high motor voltage

[muser]

If the ENN input is set high in normal operation of the TMC262(without use of external gate drivers) - then the motor will freewheel since all NMOS FET's will be switched off i.e. both top and bottom FET drive outputs.
However if an external bridge driver is used as shown in figure 23 of the TMC262 datasheet, then if the ENN pin is pulled high on the TMC262 it will set the LA1, LA2 outputs low - thus the external driver will switch the top FET's on since the external driver will simply complement the bottom gate drive signals in order to drive the upper FET's.
Therefore in order to avoid this the external high voltage FET drivers will need to be controlled via typically the shutdown input (SDN) on the external gate drivers. The ENN input on the TMC262 should be connected to 0V.
This will now support the motor being freewheeled or indeed will provide protection from any external short-to-ground circuit that can disable all FET's in the event of a s/c to ground being detected.
However I am concerned that if this situation arises for a period longer than a few seconds, the bootstrap capacitor on each gate drive chip will discharge due to there being no path to ground to keep the bootstrap capacitors charged.
In order to avoid this we could place say 100K suitably rated resistor from at least one half-bridge centre point (assuming that the motor winding will be present).
To be sure even in the event of an open circuit motor winding we would need a resistor to ground from each half bridge centre point.
With a high voltage motor supply (say up to 150V) these resistors will dissipate relatively low power in normal operation, however the resistors will prevent the boost capacitors from totally discharging during periods when the bridge FET's are all disabled.
Are there any other solutions possible for this potential problem?

[TRINAMIC_BD]

Hello - thanks for your comments and ideas - this is good input. I would do it exactly that way. Optionally, you could use the level shifters for the high side outputs of the TMC262 to drive the high side inputs of the gate driver (see fig. 25 in latest datasheet) to allow free-wheeling to be controlled by TMC262. Please be sure to insert small gate series resistors for the MOSFETs - this has been added only lately in the datasheet in the external MOSFET driver application note.

[h.singer]

Hallo,
I can either find figure 23 nor figure 25 in the TMC262 Datasheet - can you help me?
By the way. in the actual datasheet there are 2 errors in the figure 15.2 (page 47):
First: the capacitor with 4.7µF after the gate driver connects to the 2R2 of the low side MOSFET instead of the low side of the motor coil A.
Second: the value of the resistor at the collector of the BC856 must be higher (or will you put a 1.5W resistor to this place?).

[TRINAMIC_BD]

Hello,

thank you very much for reporting! We will take care and modify.
For the references in the support text above, this was related to an older version of the datasheet - this relates to chapter 15.
The resistor at the BC857 is correct - a 0603 type is enough - it does not see more than 6V.

[ronkrem]

Am I correct in assuming the comment to Figure 15.1 about "the control style in this example..." for a 4081/2 driver means adding inverters for the four H outputs and connecting the respective BM inputs to sense an output short to ground? In this case I think the inverting transistor would need to switch the AHI/BHI inputs close to the 4081 VDD voltage, so the resistor in the emitter lead could be deleted and a base resistor added for base current limiting. This implies the 262 and 4081 share the same supply voltage (10-12 volts). As you suggest, the 262 then controls safe shutdown and short-circuit protection, and the 4081 takes over dead-time control.

Seems many of us would love to see a beefed up 262!

Regards
Ron

By the way, the 4.7uF bootstrap capacitor in Figure 15.2 is still not connected correctly.

[TRINAMIC_BD]

Hi, the schematic 15.2 is corrected - do you still see the old download?
When the 262 shall monitor the BM outputs, it must be supplied with the full motor voltage - otherwise the BM inputs are not allowed to be connected to the bridge. Therefore the level shifter as in fig. 15.2 must be used. The ratio of the emitter and collector resistor determine the output voltage of the gate driver output to the external level shifter.

Yes, I understand a stronger gate driver would be nice!

[yossarian]

Hallo
Vom Regen in die Traufe.
Nun bedarf es der Korrektur der Korrektur...

Mit freundlichen Grüßen

[TRINAMIC_BD]

Oh, danke und Entschuldigung - das war zu flüchtig korrigiert --> Immer das Herstellerdatenblatt zugrunde legen.