TPS2590 Start up characteristic

Just to be sure that there is no current contribution from the input capacitance, please measure the current in the GND return side to the power supply. If you measured from the positive voltage side, there may be current from the charged input capacitor that is not seen by the current probe.

Kando-san

Many    thanks.

The data of the attached file were measured with TPS2590EVM.

Therefore, the problem of your indication does not exist.

Please check  it.

Best regards

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Katsunori HAYASHI

Engineering  Professional / Power  Management

Field  Application & Solutions / Sales  & Applications

Texas  Instruments  Japan  Limited. (TIJ)

TEL:+81-3-4331-3689          E-mail:k-hayashi@ti.com

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In both cases, there is the same capacitive load, no dc component.

In the first case, settings are IFLT is 4A and ILIM is 5A. The current peaks at 2A because TPS2590 is a power limiting cotroller. Power is limited to about 5W. (Vout  - Vin) X I out < 5. The current is limited based on the voltage and power available.  The current setting is sufficiently high to not be in limit. After the start up current peak, the voltage across the internal mosfet is dropping and the current needed to charge the capacitor is reduced.

In the second case, settings are IFLT is 1A and ILIM is 2A. This allows the voltage to come up at the power limit for the voltage across the MOSFET and potentially, the ILIM current. The current in the scope picture peaks at 1.2A so the full ILIM is not required. The controller exits the power limit mode and the current is reduced as the voltage across the MOSFET is reduced.

I know that the first case took only slightly more than 2A so it seems that limiting the second case to 2 Amps you expect the same results. It seems that there is a slight difference in the starting dynamics of the two cases that make the charge path slightly different.  

Kando-san

Many  thanks.

In your comment,
I can understand the first case.

However, I cannot understand the second case.

I think that the wave pattern photograph of the bottom shows malfunction of TPS2590.

I think that a cause of the malfunction is that ILIM and an IFLT resistance value are very big.

Please  continue investigation.

Best regards

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Katsunori HAYASHI

Engineering  Professional / Power  Management

Field  Application & Solutions / Sales  & Applications

Texas  Instruments  Japan  Limited. (TIJ)

TEL:+81-3-4331-3689          E-mail:k-hayashi@ti.com

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Kando-san

Many  thanks.

Could  you reply above  my question?

Best regards

------------------------------------------------------------------------

Katsunori HAYASHI

Engineering  Professional / Power  Management

Field  Application & Solutions / Sales  & Applications

Texas  Instruments  Japan  Limited. (TIJ)

TEL:+81-3-4331-3689          E-mail:k-hayashi@ti.com

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