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 57555 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 57555 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 9 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 9 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

Power management

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Start-Up Question of LM22672/LM22680