UCC21520-Q1: It is not recommended to leave DT floating.

Koji Hayashi92

Mastermind 6970 points

Part Number: UCC21520-Q1

Hi TI-team

My customers want to know exactly what happens when they float the DT pin.

The description of the DT pin in the past data sheet stated the following.

”Leaving DT open sets the dead time to <15 ns. ”

(Rev.B)

Could you please tell me why the DT pin shouldn't be floating and what exactly happens ?

Best Regards,

Koji Hayashi

over 3 years ago

0 Krystian Plaskota over 3 years ago

TI__Expert 4065 points

Hello Koji,

The reason we don't recommend leaving the DT pin floating because high voltage noise coupling in can disturb the deadtime duration which can cause unintended behavior from the driver.

It is best to tie DT to VCCI if not needed (allowing overlap of outputs).

Or place a 500Ω - 500kΩ resistor (RDT) between DT and GND which will adjust DT(in ns) = 10 x RDT(in kΩ). Please place a 2.2nF capacitor in parallel with this resistor as close to the pins as possible to achieve better noise immunity.

Thanks,

Krystian

0 Koji Hayashi92 over 3 years ago in reply to Krystian Plaskota

Mastermind 6970 points

Hi Krystian-san

Thank you for response.

>can cause unintended behavior from the driver.

Does this mean that the dead time will be 15ns or more, or that the dead time will not be specified ?

Also, it does not mean that the output (OUTX) fluctuates by H or L regardless of the input (INX).

Do you agree with this recognition ?

Best Regards,

Koji Hayashi

0 Krystian Plaskota over 3 years ago in reply to Koji Hayashi92

TI__Expert 4065 points

Hi Koji-san,

Leaving the DT pin floating will cause the device to set to the minimum DT, about 10ns.

This is not recommended because the DT pin in the floating state can cause the DT circuit to trigger unintentionally causing outputs to glitch low for periods of time. The actual dead time window won't vary that much.

Regards,

Krystian Plaskota

0 Koji Hayashi92 over 3 years ago in reply to Krystian Plaskota

Mastermind 6970 points

Hi Krystian-san

Thank you for response.

I understand.

I have answered my customers.

Best Regards,

Koji Hayashi

0 Krystian Plaskota over 3 years ago in reply to Koji Hayashi92

TI__Expert 4065 points

Hi Koji-san,

You're absolutely welcome! Let us know if you have questions in the future!

Regards,

Krystian

Power management

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UCC21520-Q1: It is not recommended to leave DT floating.