TPS2420 Imon output samplig with ADC - is buffer needed?

Ireneusz Magiera

Other Parts Discussed in Thread: TPS2420

Hello,

I'd like to use TPS2420 as output of 12VDC with max 1A. Datasheet contains table with values of all passive components to achieve that. My question/problem is related to Imon. It will be about 15uA (Imon=Iout/66k) for Iout=1A.To produce 2.5V output I need Rmon=158k. Do I need opamp buffer and antialiasing filter to sample Imon with 10-bit MCU ADC at 400Hz maximum? I assume that Imon changes as fast as Iout and is not averaging so with dynamic load generating spikes, dips etc. some LPF would be useful, wouldn't it?

Could you suggest a circuit to glue these things together?

over 9 years ago

0 Eric Wright over 9 years ago

TI__Mastermind 42795 points

Hello. Moving to the load switch forum.

0 Ireneusz Magiera over 9 years ago

Intellectual 335 points

Anyone? :)

0 Venkata Nandam over 9 years ago

TI__Intellectual 2800 points

Hi Ireneusz,

What is the type of load? Do you expect high frequency oscillations /spikes and dips due to load?

To reduce bandwidth, I would suggest to add a 100pF cap across the IMON resistor (158k) instead of buffer or antialiasing filter. This filter reduces IMON signal bandwidth to 10KHz. Would that be okay in the application?

Regards,
Venkat

0 Ireneusz Magiera over 9 years ago in reply to Venkata Nandam

Intellectual 335 points

Hi Venkat,
thank you for your response. It will be general purpose "power" output so type of load is hard to specify. It will be used to supply other devices, also those with DC/DC converters, so I expect spikes and dips in current. But I don't need exact shape of current draw and averaged value will be OK. Would it have sense to increase cap value to limit further the bandwidth?

One more thing that I am thinking of is response to driving EN with PWM signal, i.e 400Hz. According to turn-on and turn-off propagation delays it should be possible but I am not sure how additional circuitry will handle that.

0 Venkata Nandam over 9 years ago in reply to Ireneusz Magiera

TI__Intellectual 2800 points

Hi Ireneusz,

For general purpose power output, 10KHz bandwidth should be sufficient enough. Too low bandwidth may introduce unwanted delays.

158k and 100pF takes 100us to completely discharge. So, driving enable with 400Hz signal should be okay.

Regards,
Venkat

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TPS2420 Imon output samplig with ADC - is buffer needed?