LT8708 output current Monitor

Dear boss: 

   I wanna monitor the output current, I wanna Use mcu's ADC get the voltage from ICP and ICN , It's feasibility or not? In datasheet, In datasheet "ICN (Pin 6/Pin 6): Negative VOUT Current Monitor. The current out of this pin is 20μA plus a current proportional to the negative average VOUT current."  can anyone tell me the  proportional value From Vout Current? TKS!

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  • +1
    •  Analog Employees 
    on May 7, 2021 9:49 AM

    Hello,

    please check page 42-44 of the datasheet. There we describe the use and formulas for the required operation. The sense resistor value has to be taken into account as well, as the LT8708 measures the differential voltage between the appropriate pins and converts this into a pin output current. The resistor between the IMONXX pin and GND converts the current into a voltage which can be measured by the ADC of your uC.

    kind regards

    Markus

  • TKS, but another problem is

    1. why need "Always connect a 17.4k resistor from ICP to ground and from ICN to ground."  else resitor is okey?

    2. can we use the same ways measure input current from "IMON_INN and IMON_INP" if it's connect to uC's ADC, ADC's impedance will Affected LT8708's "IIN CURRENT MONITORING AND LIMITING",?

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  • 0
    •  Analog Employees 
    on May 7, 2021 1:31 PM in reply to xjmnn

    The ICP and ICN resistors affect internal thresholds. The 17.4K resistor requirement ensures proper operation. The IMON resistor values adjust the current limits only. If current monitoring is needed, an ADC on the appropriate IMON pin is recommended. The ADC input impedance should be large compared to the IMON pull-down resistor selected to avoid affecting the current limit setting.