Start-Up Question of LM22672/LM22680

Jayden Park

Expert 1100 points

Other Parts Discussed in Thread: LM22680, LM22672

Hi~

Out customer use LM22672/LM22680 device.

But Our customer have start-up problem.

* Condition :

- Vin : 10V, Vout : 7.1V

- Current : Nominal(Under 30mA : Non operating Motor), Active(1A, Operating Motor)

* Status :

- Start-up current is abnormal(Condition : Vin=10V, Vout=7.1V)

- Start-up current is normal(Condition : Vin=11V, Vout=7.1V)

In Light load condition, Do i need minimum gap of the Vin and Vout???

But Our customer can't change Vin level.

If see attached file, You can know status(I attached Measurement graph/ schematic and so on)

Our customer don't have many time. Please reply to me as soon as possible.

LM22672_LM22680 Question.doc

over 10 years ago

0 Frank De Stasi over 10 years ago

TI__Guru 65535 points

I am not sure I fully understand the problem.

I see two plots; one looks like very light load with ripple on the output.

The other plot shows the output voltage starting up in a jagged manner.

In both plots the output voltage is up to the desired value.

Which plot shows the problem ??

Also, what type of load are you using for start-up tests ??

An electronic load will sometimes cause problems with start-up; the best load to test a start-up

condition would be a resistor.

0 Jayden Park over 10 years ago in reply to Frank De Stasi

Expert 1100 points

Hi~ Frank.

Thank you for your answer.

Our customer's system have Start-up current spec.

So, Our customer want for Vout as follow graph at light load.

- Vout(Purple) : Red circle Line => Blue Line

Do you have solution??? Please reply to me as soon as possible

0 Frank De Stasi over 10 years ago in reply to Jayden Park

TI__Guru 65535 points

It is hard to see why changing Vin by one volt makes such a big difference.

Can you send us your schematic. Is the customer using the soft-start feature of the device ??

Perhaps a longer soft-start time would help.

0 Eddie Lee over 10 years ago in reply to Frank De Stasi

Prodigy 20 points

Hi! Frank

Schematic of Our customer refer to as follow.

Our customer did adjust 470nF to soft-start(2PIN) But test result is same.

To slove this problem, What should we doing?

0 Marc Davis-Marsh over 10 years ago in reply to Eddie Lee

TI__Genius 10095 points

Does the part start up normally if you add an additional 50mA load at startup?

Regards,

Marc

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Start-Up Question of LM22672/LM22680