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# LM43601: Inverting Buck-Boost, how long is the power off time?

Part Number: LM43601

Dear Specialists,

My customer is considering inverting buck-boost circuit by SNVA722B.

According to the application note P. 10, figure12 and figure13 show start up time, which is around 50ms.

He'd like to know how long is the power down time on the same circuit.

Is it possible to think 50ms as well as the strat up time?

Best regards,

Shinichi

• Hello Shinichi1,

Power up is controlled by soft start while power down is normally controlled by the load. The LM43601 uses diode emulation so does not pull down (actually up in this case) its output. The load and output capacitance determines how long it takes for the output to collapse.

Regards, Robert
• In reply to Robert Blattner:

Hi Robert,

As you mention, the power down time is determined by the load and the output capacitance.

In this case, I think it can calculate the equation CV=iT
At the SNVA722B, C=47uF+1uF, V=-15V, i=1A
T=0.72ms
Is it correct?

The customer'd like to know the actual value.
If possible, could you please show the actual value of the circuit(SNVA722B).

Best regards,
Shinichi
• In reply to Shinichi Inoue:

Hello Shinichi,

Your calculation is correct. In most applications, the current draw is not constant with voltage so your results will vary based on the properties of the load.

Have you checked the inverting Buck-boost design for the LM43601 in Webench? You can run simulations for this design.

Regards, Robert
• In reply to Robert Blattner:

Hi Robert,

I'll share the calulation with the customer.

I have used WEBENCH, but it can't simulate.

Could you please let me know how to do electrical simulation.

Best regards,

Shinichi

• In reply to Shinichi Inoue:

LM46001_Inverting.zip

Hi,

I have attached an example of OrCad PSPICE design for inverting on LM46001

You can download the model for LM46001 from the Tools/Software tab in the product folder of LM46001

Thanks

-Arief

Hi Arief,

Best regards,

Shinichi

• In reply to Shinichi Inoue:

No problem

Thanks
-Arief