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LTC2974 current sensing filter


I'm designing a controlled voltage source for 4 channels using a LTC2974 to control four LT3012 LDOs.

My question it's about current sensing ports. In the datasheet defines how to measure the current with a shunt resistor that includes a filter to avoid the switching frequencies from the used DC/DC converter.

I want to use a LDO regulator, the LT3012, my question is the next:

Can I quit the filtering and use directly the shunt resistor to measure the current using a LDO, or I always need to implement some filtering?

If I need the filter, to which frequency is recomendable to filter for the LT3012 LDO?

Many thanks in advance.

  • Hi Ramiro,

    Generally LDOs offer low output noise, and it's possible that you could avoid external RC filters.  If the load current is steady and you are expecting for a stable output current reading, then you will likely see accurate and consistent READ_IOUT values.  The 2974 has internal filtering, noise above 62kHz is attenuated.  Note that the 2974's ADC updates each of the channel's READ_IOUT registers every 190ms.

    Also I'd like to mention that you should place the sense resistor inside the feedback loop to avoid droop in Vout. The 3021 is capable of 500mA, and selecting the Rsense value is up to you but I suggest using a 50 milli-ohm Rsense. This will produce good accuracy at full load and also will be accurate down to 10mA.