TPS62110: Wrong Oscillator frequency

Uwe Keppler

Prodigy 50 points

Part Number: TPS62110

Tool/software:

Dear Ladies and Gentlemen,

we built a design based on your TPS62110. The input voltage of the TPS62110 is also feed to an RF output of our device.

If I measure the spectrum at the RF output I found that the TPS62110 seems to be working at 160khz instead of 1MHz.

If I use the Evalboard connected to our device I find that the switching frequency is 1MHz as expected.

So what can be the reason for this behaviour and how can it be solved.

I attached screen shots of sprectrum analyzer, schematic and layout.

Can you please give advice.

Thanks

Uwe Keppler

Polytron Electronics

5 months ago

0 Himanshu Nigudkar 4 months ago

TI__Intellectual 1850 points

Hello Uwe keppler,

Can you please share some switching waveforms as well?

Regards,

Himanshu

0 Uwe Keppler 4 months ago in reply to Himanshu Nigudkar

Prodigy 50 points

Please find waveform attached

0 Himanshu Nigudkar 4 months ago in reply to Uwe Keppler

TI__Intellectual 1850 points

Hi Uwe Keppler,

I see a 22kohm resistor on the 8V output rail. Is there any additional load on the output? If not, such a low load current would push the part into skip mode where it starts skipping 1MHz pulses to provide a better efficiency. Hence you will observe a lower frequency components as the primary one.

Regards,

Himanshu

0 Uwe Keppler 4 months ago in reply to Himanshu Nigudkar

Prodigy 50 points

Hi,

no there is no addiotnal load. As synv pin is actuallay connected to GND can it be possible that the device is in PFM mode?

Can this be the cause for the 160kHz switching frequency observed?

There is no detailed information in the datasheet about the switching frequency range in PFM mode.

0 Himanshu Nigudkar 4 months ago in reply to Uwe Keppler

TI__Intellectual 1850 points

Hi Uwe Keppler,

Yes if you connect SYNC to GND, the device will work in PFM modes at low loads. The frequency in this mode of operation would depend on the value of load. For this case, it happens to be close to 160kHz. If you want to operate the device at 1MHz, you should give a HIGH to SYNC pin:

Power management

Power management forum

TPS62110: Wrong Oscillator frequency