TPS26600-02EVM: inrush current limitin

Hi Rifo,

Thanks for reaching out!

Please do the following changes and share startup test waveform (Vin, Vout, input current in a single scope shot)

• Remove C35
• Use 100nF for C75
• Use 100nF for C77

Best Regards, 

Rakesh

Hello,

Thank you for your answer. We did the suggested changes. You can find the scope shots below.

input voltage

output voltage

input current (measured voltage across 4.5ohm so makes around 2.9A)

timing seems to be different so they were not combined in a single scope shot.

Hi Rifo,

The inrush current is mainly due to the capacitor at the input of the eFuse.

What is the Cin for the above captures? 

Is the above input voltage waveform measured before 4.5ohm or after 4.5ohm ? Can you use current probe to capture the current and multi-channel oscilloscope while capturing the test waveforms.

Best Regards, 

Rakesh

Hi Rakesh,

We measured waveform with isolated oscilloscope, probe tied to before 4.5 Ohm and ground of oscilloscope tied to after 4.5 Ohm.
But I am confused about capacitive load (Cin). Whatever I do, I will still have capacitive load (datasheet says that a minimum of 100nF should be placed) so how can I escape from inrush current? What do you recommend for the right solution. Do I need NTC or something like that?

Best Regards

Hi,

Please measure the current before the Cin. As highlighted below in the schematic, Please share startup test waveform (Vin, Vout, input current and output current in a single scope shot)

By observing Vin slew-rate, we can calculate whether the inrush current is from Cin or something else..  Iinrush current = Cin *dVin/dt

To rule out of other dependencies, you can disable the device with SHDN =GND and check the inrush current spike.

Best Regards, 

Rakesh