TPS2660: Cout Issue

Shuang Feng76

Intellectual 2990 points

Part Number: TPS2660

Hi,

If designer do not add Cout. Will there trigger any issue?

Currently without Cout, the output will output 0V when input is 8V. and Output could not up even input is 40V.

load is only 200Ω resistance.

over 4 years ago

0 Rakesh over 4 years ago

TI__Guru* 95551 points

Hi Shuang,

There is no hard requirement on the Cout value for the eFuse to function. We mention in the design example to emulate the input capacitance of the downstream DC-DC converters.

Please use the design calculator to verify the startup condition.

Best Regards, Rakesh

0 Shuang Feng76 over 4 years ago in reply to Rakesh

TI__Intellectual 2990 points

Hi Rakesh,

thanks for your note.

the picture is my issue here. there is no Cout here. When 8V and 40V with fast change. my output is not normal as you can see in the picture.

due to output is unnormal, the FLT pin also could not indicate.

For this phenomenon, do you have any comments?

hope for your suggestion and analysis.

have a nice day.

0 Shuang Feng76 over 4 years ago in reply to Shuang Feng76

TI__Intellectual 2990 points

0 Rakesh over 4 years ago in reply to Shuang Feng76

TI__Guru* 95551 points

Hi Shuang,

What is the load at the output when the Vin is back from 8V to 40V ?

Can you share the schematic ?

Regards, Rakesh

0 Shuang Feng76 over 4 years ago in reply to Rakesh

TI__Intellectual 2990 points

Hi Rakesh,

the schematic is totally focus on our datasheet.

the only different is the Cout is 0. the load is 200Ω.

ULVO is 5V, OV is 45V. I limit is 200mA

Do you have any idea about the issue in this?

One more information update to you. the same circuit, when vin from 0V to 8V, output is normal. When Vin from 0V to 40V, output is normal.

But when it change from 40V back to 8V, you can see the output turn to 0V. then Vin change from 8V to 40V, the output could not up to Vin.

if we add Cout 1uF, it could work normally, but the charge and discharge is slow.

0 Rakesh over 4 years ago in reply to Shuang Feng76

TI__Guru* 95551 points

Hi Shuang,

Do you mean the issue goes away with Cout of 1uF ?

Can you zoom-in and check the input current of eFuse whether it is getting fast-trip when the Vin is back from 8V to 40V

Regards, Rakesh

0 Shuang Feng76 over 4 years ago in reply to Rakesh

TI__Intellectual 2990 points

Hi Rakesh,

No very confuse signal when we zoom-in.

When we add the Cout, the charge and discharge is slow. so we try to move it.

as you can see, the 8V is 200us, 40V is 200us. it is very fast.

will our device could not support this kind of slew rate? and cause this issue?

hope for your analysis for this point. it is very confuse why Vin from 40V to 8V, our output go down to 0V. it is not make sense. so we try to understand it have any relationship with the slew rate we can support.