TPS62160-Q1: TPS62160-Q1 designed for 3.3V,but it generates 3.19V only

Hello Ebin,

Are the resistors R1 and R2 rated for 1% or 5% tolerance?  If 5% resistors were used then a worst case of 3.07V could show up on the output voltage given your selection of R1 and R2.

For your application of 12V to 3.3V regulation it may be advantageous to use the TPS62162-Q1 version of this part that is already programmed to output 3.3V. It doesn't require the use of R1 and R2 which reduces the number of parts for the design.

Another reference for this is found in the datasheet in Section 9.2.2.1.

Thanks,

Joseph

Dear Joseph,

1% resistors are used in feedback circuit. We cant able to change the part since we already manufactured the boards.

Regards

Ebin

Dear Joseph,

I have cleaned the area of FB pin and ensured that there is no flux. Both R1 & R2 are 1% tolerance.

Regards

Ebin

Hello Ebin,

The 1% resistors should be good on the tolerance. The value of the feedback resistors could also be lower to increase accuracy (ex. R1=47K, R2=15K). This would draw slightly more current from the output but could help with accuracy issues.  This also may not be helpful if you can't change the manufactured boards.

Where are you measuring the output voltage from (left or right side of the ferrite bead)?

And under what load conditions are you testing (full load, no load)?

It may be helpful to have measured waveforms of Vout (both sides of the ferrite bead), and Vfb if a test setup is available. This would help us debug the situation further.

Thanks,

Joseph

Dear Joseph,

I have tried with the resistors 47K & 15K, but the result is same. I have attached the waveforms of Vout after & before ferrite bead and also for the feeback voltage. I have tested with load & no load conditions, both shows same result. All ICs are working fine which is connected to this 3v3 rail.

Regards

Ebin

Hi ,

Conrad will reply later.

BRs,

Young

Hello Ebin,

The output voltage at 3.22V is reasonable because the TPS62160-q1 has feedback voltage accuracy of +/-3% in PWM mode.

My recommendation would be to recalculate the resistors to give a slightly higher output voltage to compensate for this accuracy and for the voltage drop across the ferrite bead.

I calculated 1% resistors to be R1=48.7k, R2 = 15k (you can also try R1=487k, R2=150k if it is more convenient for your design), 

 I used Vref=0.78V (per your measured value) and calculated Vout = 3.312V. 

If you want more margin (slightly higher output voltage) you can even use the next highest 1% resistor for R1 (49.9k).

Let me know if this helps.

Thanks,

Joseph