TPS62147: Switching frequency in case of forced PWM mode

Hi Yoshifumi, 

What inductor are you using for your design?

Because this device uses the DCS-control mode, there may be some variation in frequency from the measured data on the EVM. 

Also, here is an Application Note on DCS-Control frequency variation for your reference.

Thanks,

Joseph

Hi Joseph,

Thank you for your reply.

I am using 1.0uH inductor (DCR=24mΩ). I understand that DCS-control mode is used.

Is it possible to calculate or estimate frequency?

Best regards,

Yoshifumi Shimojima

Hi Yoshifumi,

For switching frequency calculations check equations (1) and (3) in the datasheet. 

After calculating ton, calculate toff = ton * (1-D)/D, where D = Vo/Vin. Then FSW = 1/(ton+toff).

Do you have a schematic for your TPS62147 design? 

Thanks,

Joseph

Hi Joseph,

Thank you for your reply.

My design is ≒ Figure 87(Multiple Loads) in the datasheet. Deferences from Figure 87 are no multiple load, EN is enabled after VIN rised, and VIN = 5V, VOUT = 1.2V.

I am sorry there is no image.

Hi Yoshifumi,

Are you using a similar layout to that specified in the datasheet in section 12.2?

Can you also tell me what efficiency you are measuring at this operating condition?

Thanks,

Joseph

Hi Joseph,

I am sorry for my late reply.

I am using a similar layout to that specified in the datasheet in section 12.2.

I have not measured efficiency yet.

Best regards,

Yoshifumi Shimojima

Hi Yoshifumi,

Below is a capture of SW node showing switching frequency:

Vin = 5V, Vout = 1.2V, Iout = 20mA, L = 1uH

FSW =~ 1.66MHz, with ton = 144ns.

Thanks,

Joseph

Hi Joseph,

Thank you for your information. I understand that the frequency can be 1.6MHz.

I measured the efficiency, and it is approximately equal to the value in the datasheet. (It is within 5% of value of the datasheet at 20mA～1A)

Best regards,

Yoshifumi Shimojima

Hi Joseph,

Thank you for your checking.

Best regards,

Yoshifumi Shimojima

Hi Yoshifumi,

For no further question, I will close the case.

BRs

Zixu