lm5175 / tolerance of parameters

ACGUY

Guru 11170 points

Other Parts Discussed in Thread: LM5175

Hi all,

I have any questions.
Please let me know about LM5175 for design.

[1]
On equation (5), has two numbers "200 ns" and "37 pF".
How much the tolerance for their?

[2]
About mode setting resistor, I finded resistance 93.1 kohm from datasheet.
How much the tolerance?

Regards,
Nagai

over 7 years ago

0 Vijay86929 over 7 years ago

TI__Genius 11490 points

Hi Nagai,

These numbers are obtained through curve fitting. To get an idea of tolerance please look for the respective parameters (Fsw and MODE thresholds) in the electrical characteristics table.

Thank and regards,

0 ACGUY over 7 years ago in reply to Vijay86929

Guru 11170 points

Vijay-san,

In other words, are these tolerances unknown?

Regards,
Nagai

0 Vijay86929 over 7 years ago in reply to ACGUY

TI__Genius 11490 points

Hi Nagai-san,

The tolerance on Fsw and MODE voltage threshold are in the Electrical Characteristics table in the datasheet.

Regards,

0 ACGUY over 7 years ago in reply to Vijay86929

Guru 11170 points

Vijay-san,

I saw the datasheet about tolerance of fsw by Rt.
- When Rt = 133kohm, fsw = 200kHz +/-10%.
- When Rt = 47kohm, fsw = 500kHz +13%/-14%.
These tolerances are not equal. Why not equal?
I think, 200ns and 37pF have tolerances too.
Please tell me the calculation formula or target width for design.

Regards,
Nagai

0 ACGUY over 7 years ago in reply to ACGUY

Guru 11170 points

- Please answer by 9th.

0 ACGUY over 7 years ago in reply to ACGUY

Guru 11170 points

Please answer by 14th december.

0 Vijay86929 over 7 years ago in reply to ACGUY

TI__Genius 11490 points

Hi Nagai-san,

The equations in application section a a curve fit for the graph (Figure 3 in datasheet) which shows the typical RT-Fsw relationship. The "FREQUENCY" section of the Electrical table (Page 6) shows variation (tolerance) for a given typical frequency setting.

This is the standard way of presenting data in the datasheets. The actual variation that you will for a given RT setting is likely to be very small.

Regards,

Vijay

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lm5175 / tolerance of parameters