New issue:how to improve drive capability?

Hi Chao,

The DRV8301 is the strongest gate driver in our portfolio.

The DRV8301 has an average gate drive current of ~30mA. If you know the Qg(TOT) of your MOSFETs you can get a calculation for how fast you can switch.

60 MOSFETs is a large amount. How much current are you looking to drive? What is your power supply?

Hello Nick.

I want to design a BLDC motor driver which can withstand high current(400A).So I have to make some MOSFETs parallel.

PWM frequency is 20KHz.

The DC bus voltage is 48V.

My schematic:3107.POWER.PDF

chao,

I know of a customer using IS-FOC and DRV8301 to drive 350A+.  He is simply // the FETs, but in this case we are talking 12 FETs, maybe 24 at the most. Not 60!

Hello Chris.

Because of the temperature and some  energy losses ,I can not reduce quantity.

Can I increase some push-pull transistor amplifiers(PNP+NPN)  in the back end of DRV8301? But I do not have a specific and reliable circuit.My application is electric vehicle driving motor.

chao

Hi Nick.

Everything was ok,when I used 6 MOSFETs.Afterwards I used 18 MOSFETs to do an experiment.I looked at the OCTW signal when I run project 02a.I saw it emerged some voltage fluctuations and the LED glowed weakly.motor detection was failure,as shown

As if it had no overload completely.I do not know what is causing it.

The case seemed to happen,If only MOSFETs were used in parallel connection mode.

I can't find the reason,I need help.

chao

Hi Chao,

What is the PN of the FET you are using? Does the issue happen with no motor connected (do the outputs switch with no load)?

Can you check the status of nFAULT along with nOCTW. There is a table in the DRV8301 datasheet that points to the fault condition based on the status of these pins. You can also read the SPI register.

Hello Nick.

The mosfet I used is AUIRFS4010-7P.0763.AUIRFS4010_7P.pdf

I am sure My BLDC motor has been connected with the board.

The level of nFAULT kept high at that time.

I did not use SPI communications,so I did not have any hardware connection about SPI. Does the issue happen 

For this reason?

This is my schematic:4478.Sheet1.PDF

Hi Chao,

It would be good to perform a test with no motor connected to rule that out as an issue. Then we can work from there. The next step would be to try switching at much lower frequencies.

But still, I don't believe the DRV8301 can drive this number of FETs at a reasonable frequency.

Your FET has a Qg of 150nC. The DRV8301 can support ~30mA continuous. 30mA / (60 * 150nC) =~ 3000 Hz.

Hello Nick.

New,I have finished an experiment:I did not connect motor and used 12 MOSFETs to run lab02a.

All appeared well when I set PWM frequency = 10K~30K.

The OCTW PIN and FAULT PIN became low level and two leds gave out dim light ,when I set PWM frequency = 30K~45K.

The waveform of OCTW PIN:

The waveform of FAULT PIN:

I think drive capability is not enough.Does TI have another components to enhance drive capability or solution about circuit structure?

chao

Hi Chao,

We do not have a larger gate driver in our portfolio at the moment. You will either have to reduce the PWM frequency, reduce the number of MOSFETs, or find a MOSFET with a lower Qg.

The MOSFET you are currently using has a relatively large Qg so option three may be a good option to investigate.

Nick.

Can I add push-pull circuits on the PWM output side of DRV8301 to enhance drive capability ?

Is it correct?

I do not  have more design experience about this circuits.

Hello

48 V,400A ! How efficient is this motor and where it is used?

400A is phase current or total DC bus current?

Just curious

Andrey 

It is used for electric vehicle.400A is phase current.

chao

Hi Chao,

How would you source Vcc in this scenario? The main difficulty in double N-channel half-bridge configurations is generating the PVDD + 10V supply.

Hello Nick.

How would you source Vcc in this scenario? 

Can I make a DCDC converter (48V to 15V)? Like flyback.

The main difficulty in double N-channel half-bridge configurations is generating the PVDD + 10V supply.

Sorry,I can't understand quite clearly.Could you be more specific?

Thanks

chao.

To enable a standard level n-channel MOSFET you need approximately +10V from Gate to Source. Source will fly up to PVDD when the high side MOSFET is turned on. To keep the high side MOSFET fully enabled you will need to generate PVDD (source) + 10V for the gate.

The DRV8301 does this with a bootstrap capacitor and a trickle charge pump. It is running out of charge to enable all the MOSFETs in your configuration.

I see. That means I have to make four different VCC power supply (VCC1,VCC2,VCC3 for high side,VCC4 for low side.),if I want to add push-pull circuits on the PWM output side of DRV8301.Right?

If so,I think it will influence costs problem and increase system complexity,This is really a problem...... ⊙︿⊙

Many thanks for your kind response and immediate follow up.

chao.

Hello Chao

IXYS has 9Amp Gate Drivers.

As i read in papers, electric cars have 300-600VDC bus.Then one can reduce phase currents in the traction motor/motors.

48VDC bus I saw in EBIKES and probably in golf cars.

400A phase current is huge, a welder has 200A current.