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# TPS62130A-Q1: frequency setting and result

Part Number: TPS62130A-Q1

I setting the switching frequency as 2.5MHz.

but why in my measurement the maximum switching frquency only 1.56MHz.

for variable switching frequency, how can I calculate the indutance?

my condition:

Vin=8V, Vout=1.09V, Iout=2.6A.

• Hi Viola!

This device does has such wide frequency. Pls see below figure in DS.

I suggest you directly choose 2.2uH L and 22uH Cout. This solution has been validated a lot.

Shuai

• did you know how to calculate the frequency @Vin=8V, Vout=1.09V? did there have any fomula can share?

and

from datasheet it shown the duty will larger than 20%.

but from my EVM board test, it was 16%@Vin=8V, Vou=1.09V, Iout=2.6A, L=2.2uH

why the duty can less than 20%?

thank you.

BR,

Viola

• Hi Viola!

The duty cycle is basically determined by Vout/Vin. Also it is also determined by loading as there  is some IR drop caused by Rds_on and inductor DCR, but these factors aren't critical.

We don't have a such accurate formula. But you can use 1.56Mhz as a typical value to guide your inductor design, it doesn't have any risk.

Shuai

• Hi Shuai,

Although the fomula on datasheet shows the minimum duty is 20% isn't consider the IR drop caused by Rds_on and inductor DCR...

if consider the factor, duty will less than 20%, right?

thank you.

BR,

Viola

• hi

Even we don’t consider it drop，1.09/8 is still less than 20%

• hi

that's my confuse. because on datasheet is shows " an absolute minimum on-time of about 80ns is kept to limit switching losses".

and the fomula is ton =Vout/Vin*400ns=> Vout/Vin will more than 20%

• Hi Viola,