DRV8353R: DeadTime

NIKOLAOS ADAMOPOULOS

Prodigy 110 points

Part Number: DRV8353R
Other Parts Discussed in Thread: DRV8353, DRV8302

Hi all,

The datasheet of the DRV8353 does not refer to external minimun MCU deadtime.

The IC itself has a sophisticated way to insert the deadtime via tdrive added to the SPI_Config_DeadTime.

My understanding is the the tdrive is adjustable even if you can set its maximum value via SPI.

My question is if you insert an external deadtime to the device, what is going to happen? How the times will be added?

For better performance do we have to avoid the use of external deadtime and let the device decide it ?

Thank you,

Nick

over 5 years ago

0 Adam Sidelsky over 5 years ago

TI__Guru 66130 points

Nick,

Thanks for posting on the MD forum!

There are two parts to deadtime inside the device, a fixed component (tDEAD), and a dynamic component. You select the tDEAD and the device inserts additional time as needed while monitoring the gates for a safe time to switch.

Adding external dead time is fine, this will probably be longer than tDEAD or the inserted dead time so the external dead time will over-rule the internal timing assuming it's more. If external dead time is smaller than tDEAD plus the internally inserted extra time then the external dead time will essentially be ignored.

Regards.

-Adam

0 NIKOLAOS ADAMOPOULOS over 5 years ago in reply to Adam Sidelsky

Prodigy 110 points

I assume that the SPI config of the TDRIVE is only the maximum time that IDRIVE is driven.

After TDRIVE if the mosfet gate has not been in VGS, the fault will be triggered.

However, this does not mean that the driver will push IDRIVE for TDRIVE time if is not needed, right?

I am asking all the above as I am trying to figure out the differences between the drv8302 and drv8353. I jumped to drv8353 but now my mosfets are running 15C hotter under the same running conditions, while all the rest are still the same.

0 Adam Sidelsky over 5 years ago in reply to NIKOLAOS ADAMOPOULOS

TI__Guru 66130 points

Nick,

Yes this is correct, if the input command is changed before TDRIVE expires then the remaining TDRIVE is cancelled.

If you are having heat issues it may be your IDRIVE setting. Could you tell us your FET configuration, FET Qgd, IDRIVE selected, gate trace width?

Regards.

-Adam

0 NIKOLAOS ADAMOPOULOS over 5 years ago in reply to Adam Sidelsky

Prodigy 110 points

Mosfet: BSC034N10LS5

Qg (total) = 37 - 46nC

IDRIVE ON = 100mA

IDRIVE OFF = 300mA

Rgate (on)external = 10ohm

Rgate (off)external = 3.3ohm

Trace width = 0.5mm

0 NIKOLAOS ADAMOPOULOS over 5 years ago in reply to NIKOLAOS ADAMOPOULOS

Prodigy 110 points

I have also tried with 3 x IDRIVE the above current, and got some degrees less 3-4C.

But i think that there maybe another issue somewhere.

0 Adam Sidelsky over 5 years ago in reply to NIKOLAOS ADAMOPOULOS

TI__Guru 66130 points

Nick,

Traditionally my customers don't use gate resistors and aim for 100-200nS of VDS rise/fall time, how much are you getting with each of the IDRIVE settings mentioned?

Do you see any overshoot/undershoot on the gate or source nodes when the gates switch?

Can you share your schematic and layout?

Regards,

-Adam

0 NIKOLAOS ADAMOPOULOS over 5 years ago in reply to Adam Sidelsky

Prodigy 110 points

0 Adam Sidelsky over 5 years ago in reply to NIKOLAOS ADAMOPOULOS

TI__Guru 66130 points

Nick,

Sorry, it's hard to tell from the layout, how thick are the gate and source traces?

From the scope plots we can see that there is a lot of overshoot/undershoot/ringing on the gates. I would recommend lowering the IDRIVE until you no longer see this ringing behavior because it is undesired and may be causing your issues.

Regards,

-Adam

0 NIKOLAOS ADAMOPOULOS over 5 years ago in reply to Adam Sidelsky

Prodigy 110 points

Hi Adam,

width of the traces is 0.5mm as I said above.

There is ringing on the gate which could lead to slow down a bit the mosfets but not that much of concern.

More importantly I am worrying about the losses difference between the 2 drivers.

0 Adam Sidelsky over 5 years ago in reply to NIKOLAOS ADAMOPOULOS

TI__Guru 66130 points

Nick,

Sorry for the delay here, did this get resolved? I know there was an email chain as well.

Regards,

-Adam

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DRV8353R: DeadTime