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TPS92200: minimum inductor current reported in datasheet

Part Number: TPS92200

Note: since the original thread was deleted, I am posting this question again, as suggested here:

Where is my post?

I am not enclosing all the messages in the original thread (for example, those to avoid it be closed automatically).

07/04/2022  *************************************************************************************************************************************************************************************

Dear TI experts,

the datasheet (SLVSER4 –MAY 2020, par. states:"For TPS92200, the inductor current ripple is also suggested to be larger than 300mA to guarantee loop stability.
If the calculated inductor current ripple is less than 300mA. Smaller inductor is suggested."

I found the same requirement also in "TPS92200 Application Calculation V1.0.xlsx".

Could you please explain where does this value come from? Does it not depend on Vin and/or Vout?

11/04/2022  -  Yuting Shao   ********************************************************************************************************************************************************************


TPS92200 adopts peak current control method, which means chip needs get enough inductor peak current to achieve stable control. If the current ripple is too small, the control loop maybe unstable.

This value is a recommended value according to device internal components and experience. If 300mA is met, for the whole working range, device will work normally. 



11/04/2022  *************************************************************************************************************************************************************************************

Hi Robin,

Thanks for your answer.

Note: for all the sentences and equations below, I am referring to the same paragraph of the datasheet mentioned above; they are the same also in the latest issue of the document (January 2022).

In my application:

Vout = 9.7V

Vin(max) = 28.6V

Iout = 140mA (current through the LEDs)

So to have 300mA in equation 3, you must have a maximum inductor value of about 21uH. To have this value as result of equation 2 (same paragraph), Kind should be greater than 2.

You could get the same result by the definition of Kind (amount of inductor ripple current relative to the maximum LED current), being in my application 300mA more than double Iout.

The same paragraph states that, in general, the value of Kind is suggested beetween 0.2 and 0.4. Does this mean that in my application (and, more generally, for all the cases where Iout is lower than 750mA, i.e. 300mA / 0.4 ) TPS92200 is not recommended?

If this is not the case, could you please specify the maximum Kind, and so the minimum Iout value?

12/04/2022  -  Yuting Shao   ********************************************************************************************************************************************************************


Let me have a check firstly and reply you later.


  • hello Tessitore

    understand your point here. let me clarify the considerations for 300mA ripple current and Kind.

    As you know, TPS92200 adopts peak current mode control, which means inductor current is sensed back to realize more fast regulation compared with voltage mode control. Here if 300mA inductor current is not met, the system will behave more like voltage mode control and under current compensation parameters, it is likely to cause unstable condition. That is why TI requires user to meet 300mA inductor current ripple during design stage.

     However, it is also mentioned the ripple cofficient Kind should be within 0.4. This is for the conderation of loss on inductor, internal Fet and other passive componets. Normally larger ripple current will casue higher DC/AC inductor loss and Fet switching/conducting loss. But Kind here is a general range and for low current conditions, thermal will not be a big concern.

    Basically, requirement of 300mA ripple current has high priority than the range of Kind. Hope this helps.