UCC21755-Q1: AIN pin

Shishir Trivedi

Part Number: UCC21755-Q1

Hi,

Is it possible to use the UCC21755-Q1 AIN pin to sense output ac voltages or currents, also what are the other use cases of the AIN pin except dc-link voltage sensing and temperature sensing as I see the input voltage is limitied to only positive values. Can you please share some reference design in the case ac quantities are measureable through it.

over 1 year ago

0 Pratik Adibatla over 1 year ago

TI__Expert 7473 points

Hi Shishir,

Thanks for reaching out. Please refer to the app notes below:

Performance of the Analog PWM Channel in Smart Gate Drivers (ti.com)

UCC217xx Family Driving and Protecting SiC and IGBT Power Modules and Transistor (Rev. B)

Best,

Pratik

0 Shishir Trivedi over 1 year ago in reply to Pratik Adibatla

Prodigy 80 points

Hi Pratik,

I went through the documents you had referred me to. However, in the document " Performance of the Analog PWM Channel in Smart Gate Drivers ", in figure 7 there is an op-amp tied to Vcc (input logic side supply). If that is the case then the input loses its isolation function as the AIN is a secondary side pin. Also, can you share the values of the passives and opamp so that I can simulate the circuit given in fig. 7.

Thank you,

Shishir

+1 Pratik Adibatla over 1 year ago in reply to Shishir Trivedi

TI__Expert 7473 points

Hi Shishir,

That's a good point. In that case VDD can be used or a step-down voltage from VDD can be applied as well to maintain the isolation requirement. Otherwise, a RECOM isolated bias from VCC can be used as well. Unfortunately, we don't have the values of the passives as it is just a reference which highly depends on the in-line current from the motor. The user has to design for themselves.

Best,

Pratik

0 Shishir Trivedi over 1 year ago in reply to Pratik Adibatla

Prodigy 80 points

Hi,

Thanks for your quick response. I understand that the passives highly depend on the values of quantity to be sensed by the user. However, the part that bothers me is the opamp as I am unfamiliar with their design. Can you recommend a family of such an opamp that could be utilized here so that there is no error(delay, rating etc.) in the design part.

0 Pratik Adibatla over 1 year ago in reply to Shishir Trivedi

TI__Expert 7473 points

Hi Shishir,

Thanks for your interest. Please refer to the page below for our range of products:

Operational amplifiers (op amps) product selection | TI.com

You can use the filter options and choose the desired one based on your requirements and raise a separate e2e based on that if you have questions and our experts from the Op-Amp team will reach out to you.

Best,

Pratik

0 Shishir Trivedi over 1 year ago in reply to Pratik Adibatla

Prodigy 80 points

Hi Pratik,

Just one more doubt while going through the 'Performance of the Analog PWM Channel in Smart Gate Drivers (ti.com)'. How does the measured ac quantity (say ac line current of the inverter) translate from sinusoidal input at the AIN pin to the APWM output which is supposed to be varying only in terms of duty cycle. How can an user realise the rms values of the ac currents using the configuration shown in the document.

0 Pratik Adibatla over 1 year ago in reply to Shishir Trivedi

TI__Expert 7473 points

Hi Shishir,

The output at APWM is always a PWM signal which is then converted to an analog signal using an RC filter. Typically, customers have a nice MCU to measure the duty cycle precisely or do the appropriate conversion from Vain to the in-line current rms value and set the threshold accordingly.

In the datasheet, the below is how the voltage at AIN is converted to duty cycle at APWM with the tolerance provided in the datasheet.

The conversion from in-line current to AIN would depend on the application and selection of the passive components for the op-amp.

Best,

Pratik

Power management

Power management forum

UCC21755-Q1: AIN pin