REF3450: Temperature Affection Turn on Time

Masayuki Uchihara

Part Number: REF3450

Hi Team,

Does turn on time have dependency of temperature? This is because our customer check the Vout turn on time behavior of across temperature. They can see like figure as below. the red line is on datasheet. I add the blue line to explain the phenomena. Why is the turn on time of the blue line(Ta=105C) higher than the red line (Ta=25C).

Thanks,

Uchihara

over 4 years ago

0 Marcoo Z over 4 years ago

TI__Mastermind 19370 points

Hi Uchihara-san,

I have not heard of a temperature dependency on turn on time before.

Let me test this in the lab and ask my internal team.

Is there minimum start up time that is needed or is this causing an issue?

What size of input/output capacitor is your customer using? Is the capacitor also exposed to the heat?

-Marcoo

0 Marcoo Z over 4 years ago in reply to Marcoo Z

TI__Mastermind 19370 points

Hi Uchihara-san,

I tried testing REF34 family in the lab and I did not see such a drastic difference with start-up time over temperature.

Do you have a schematic I can try?

What type of capacitors are they using for input bypass and Cload?

Could this be just variance due to capacitors over temperature?

0 Masayuki Uchihara over 4 years ago in reply to Marcoo Z

TI__Intellectual 1635 points

Hi Quote,

the input capacitor is 1uF. The output cpacitor is 10uF. The load is 2.5 ohm

The capacitors are ceramic.

Can you try this? If possible, I want to see the test result.

Thanks,

Uchihara

0 Marcoo Z over 4 years ago in reply to Masayuki Uchihara

TI__Mastermind 19370 points

Due to US holiday, i can't test this until next week but i will see how it varies. Can you confirm if by 2.5 did you mean 2.5k?

0 Masayuki Uchihara over 4 years ago in reply to Marcoo Z

TI__Intellectual 1635 points

Hi Marcoo,

Sorry for typo. Yes. You are collect. The 2.5 kohm is collect information.

0 Marcoo Z over 4 years ago in reply to Masayuki Uchihara

TI__Mastermind 19370 points

Hi Uchihara-san,

I tested had similar results to the graph you posted.

The 10uF ceramic capacitor dropped to 5-6uF at 125C. This is the reason why the start-up varies so much. From 25C to cold, the capacitance is more consistent so the start up won't varie.

-Marcoo

0 Masayuki Uchihara over 4 years ago in reply to Marcoo Z

TI__Intellectual 1635 points

Hi Marcoo,

That's make sense regarding high temperature. But I have question about cold temp.

The turn on time is low speed in cold temp compared with high temp even the capacitance should be changed to low value.

How do you think about it? Doesn't the soft start have temperature dependency?

Thanks,

Uchihara

0 Marcoo Z over 4 years ago in reply to Masayuki Uchihara

TI__Mastermind 19370 points

Hi Uchihara,

The capacitance that I measured was higher at cold so it is slower. The higher value of capacitor requires longer time to charge.

I would ask your customer to measure their capacitor across temperature and see how it changes. I feel it will match the start up timing.

The soft start has a very minor soft start dependency but the soft start won't trigger unless the current is higher >19mA. So this would not apply for this circuit. Because the inrush in closer to 6mA.

-Marcoo

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REF3450: Temperature Affection Turn on Time