TPS62132: Lowest limit of switching frequency

legacy_love

Prodigy 40 points

Part Number: TPS62132

Tool/software:

Hello!

I have a question on the switching frequency range of TPS62132RGTR.

I found this figure on your datasheet, which shows that the switching frequency decreases

according to the amount of output current. From this figure I can read 2.5MHz@400mA,

so 250kHz@40mA if I estimate the value proportionally.

With my application,

Vin: 12V

Vout:3.3V / Iout:30-50mA

Cin:10uF / Cout: 22uF / Lout: 2.2uH (as recommended)

I observed the switching frequency of approx.6kHz, which is

much lower than the estimation above. (Waveform:Vout)

Now questions are:

1. what switching frequency shall I expect, as a design value or a typical value, at the current range of 30-50mA?

2. Is there any lowest limit of the frequency, or is it really 0Hz at 0A?

3. If possible, can you judge whether my waveform is normal or not?

Thank you in advance!

5 months ago

0 Himanshu Nigudkar 5 months ago

TI__Intellectual 1850 points

Hi,

Can you please share the schematic as well to help you better?

0 legacy_love 5 months ago in reply to Himanshu Nigudkar

Prodigy 40 points

Hi, thank you for your contact.

Here's related schematic, which is according to the reference design in the datasheet.

0 Himanshu Nigudkar 4 months ago in reply to legacy_love

TI__Intellectual 1850 points

Hi,

I don't see any load connected in the schematic. For this scenario, the switching frequency is supposed to go very low. Please let me know if you are using any load on top of this.

Regards,

Himanshu

0 legacy_love 4 months ago in reply to Himanshu Nigudkar

Prodigy 40 points

Sorry details of the loads cannot be disclosed, but they are microprocessors.

Could you clarify the term "very low"; No.2 of my question lists which I sent earlier, is whether any lowest limit exists.

0 Himanshu Nigudkar 4 months ago in reply to legacy_love

TI__Intellectual 1850 points

Hi,

There is no limit on the lower end as such. Depending on the load, the device may switch once and deliver all the energy needed to maintain the output voltage and stay quiet for a long time. Is the continuous load 30-50mA or it varies with time and the average value is 30-50mA?

0 legacy_love 4 months ago in reply to Himanshu Nigudkar

Prodigy 40 points

Hi,

It is continuous, although there may exist small current ripple.

0 Himanshu Nigudkar 4 months ago in reply to legacy_love

TI__Intellectual 1850 points

Hi,

I see PWR_FLAG connected on 3.3V output, can you please confirm where all the flag is connected in your system. Is there any possibility of leakage current getting injected because of this flag?

0 legacy_love 4 months ago in reply to Himanshu Nigudkar

Prodigy 40 points

Hello,

No, PWR_FLG is only necessary as indicative information for design the rule checker.

There is no other power supply nor leakage path.

The output of this device is connected only to a microprocessor and external sensor devices.

0 Himanshu Nigudkar 4 months ago in reply to legacy_love

TI__Intellectual 1850 points

Hi,

I dont see any other way this can reduce the frequency. Is the phenomenon repeatable? If yes, we can try to reproduce it in our lab and debug the issue.