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# UCC21540A-Q1: Common Supply for 3 driver ICs

Part Number: UCC21540A-Q1

Hi sir,
We are planning to use UCC21540AQDWKRQ1 driver IC to drive high side and low side FETs in the same leg of a 3 phase inverter in motor drive application. Since there are 3 such legs we are planning to use 3 such driver ICs. Can we provide a common high side supply for all three ICs or should we provide 3 supplies for 3 ICs individually?

Can we also use same supply for both VDDA and VDDB ?

• Hi Harish,

There are two ways this could be implemented.

1- You can have a dedicated supply for each of the channels. Important to know that this supplies must be able to be floating for the HS driver.

2- You can implement a bootstrap circuit that will help you create the bias for the HS driver. To give you more information I have attached two documents here. The first document is a complete documentation about the bootstrap circuit design. I encourage to read this document since this part of your circuit is very important. The second document is a calculator that will help you design for the capacitor and resistor on the bootstrap based in your circuit information.

https://www.ti.com/lit/zip/sluraz5

Thank you very much for reaching out and let me know if you have any further questions. If this solved your question, let us know.

Best

Francisco Lauzurique

• Thank you for your response sir,
Okay So I would like to use single supply for both VDDA and VDDB with bootstrap circuit.
Can I use same supply for 3 ICs driving 6 FETs in 3 legs?

• Hi Harish,

You can use one driver for each half bridge. You need to ensure that the driver capabilities are enough based on the devices you are driving. In our datasheet there are example applications that will walk step by step of the calculations.

Best

Francisco Lauzurique

• Yes sir, we are using 3 drivers for 3 half bridges. My question is can we use same output supply source VDD for all 3?

• Hi Harish,

If all ground voltages are the same in every cycle, then yes, you can use the same source for all the LS. However, you should ensure the bootstrap is fully charge or enough charge to be able to turn ON the HS device. There will be limitations in the duty cycle for your architecture.

Best

Francisco Lauzurique

• Yes sir all the ground voltages are same. So that means I can give one supply to VDDA, VDDB of 3 drivers to drive 6 fets (3 high and 3 low) of a 3 phase inverter circuit and I should provide bootstrap circuits to the 3 high side fets. Am I correct sir?

• Hi Harish,

That is correct. If all ground voltages are the same in every cycle the same supply can be used for all three half bridge gate driver IC's in a bootstrap configuration. The bootstrap circuit will need to be fine tuned to ensure the bootstrap capacitor gets enough charge to turn ON the HS (High side) fets.

Please refer to the application note and calculator mentioned above to aid with the design process.

Best regards,

Andy Robles