• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 348 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

UCC2897A: VREF loading and VDD,PVDD supply from Bias winding

Felix Arul Rajesh Francis
Intellectual 480 points
Part Number: UCC2897A
Other Parts Discussed in Thread: ISO7742, ADS7924,

Hi 

3 points would like to clarify on this thread

We have 1 ADC (ADS7924), 1 Isolator (ISO7742) & 1 comparator (TLV4082DBV) in our design.

This takes 3.3V  and 3mA current altogether. 

These devices are powered on the ACFC primary domain (54V and 54V_N).

Instead of using a 54v to 3V3 switching regulator, we would like to source it by one of the below two options

a. from the VREF (5V) voltage of UCC2897A by  stepping down it to 3.3V either by diode or resistor divider. would that be feasible?

b.  from the bias winding supply (12V to the UCC2897A VDD & PVDD) through a Zener regulator of 3.3V. The bias winding is comfortably can source 30mA as it is designed for max of 170mA

We tried this method but the ACFC generation (20V) is not happening. Any thought on this? 

VDD, PVDD current consumption:

The current consumption on the  VDD & PVDD is measured as 20mA, when sourced through a 12V bias winding supply.

As per datasheet, load on VDD is very less (around 3mA) and its Vdd voltage range is 8.5 V – 12V – 16 V.

Does the PVDD can take more current in this case? So that we are measuring 20mA.

What would be the maximum supply current for Vdd and Pvdd for our case: Vin = ~ 54V and operating temperature = 0 C to ~ 100 C and XFMR bias voltage = 12 V @ 20 mA?

We would like to source more current from this winding to realize the above mentioned requirement (b) through a Zener regulator (12V to 3.3V with 3mA for circuits).

Regards,

Felix.

  • 0
    TI__Guru 74115 points

    Hi,

    1) VREF is intended only for feedback with very limited loading capability (< 5mA). So you need to calculate all loading on VREF to make sure. As overloading VREF will make the IC mal-operation.

    2) From bias winding is ok as the bias current can be designed externally. I am not sure what you mean you cannot get 20V from your aux. You need check the pulses to debug if your aux and associated circuit is designed and built properly.

    3) It sounds you measure the current of VDD and PVDD together. But you should measure each. PVDD current is on your MOSFET selected and frequency selected. if your MOSFET needs higher driving current PVDD current becomes bigger.

    4) Again the aux winding and aux for bias is on external design.