Measuring Current with LTC2977 or LTC2975

Hello 

I'm designing a new system. I would like to use a PowerManager. 
I need to control the current and voltage of 4 supplies. 
Now I have seen, that I could use a LTC2977. It allows to use the odd channels to be configured as current sens. This would reduce the 8 available channels to 4.  
Or I could use a LTC2974/5 having 4 channels but each channel can do current and voltage. 

Which solution gives better performance? (More exact current reading and voltage control?)

Thank you for your help

Kind regards
Botnic

Parents
  • +1
    •  Analog Employees 
    on Apr 20, 2020 4:41 PM

    Hi Botnic, 

    If you plan to use 4 channels to monitor voltage and 4 channels to monitor current, I would recommend the LTC2974 or LTC2975. This is exactly the app that were designed for.  The difference between the 74 and 75 is the input supply current measurement capability of the 2975.  The 2974/75 and 2977 are the same with regards to servo/margining,sequencing, voltage sensing & measurement accuracy, OV/UV fault detection, and so forth.

    The big advantages of the 74/75 are the dedicated current sense pins and current related configuration registers that allow the user to program the Rsense value and readback registers are already converted to Amps.  READ_IOUT (74/75) accuracy is 0.3%, while the 2977 is current mode is 0.7%.  Accuracy in most cases is dominated by Rsense computed value vs actual sense resistance or DCR value for the inductor. The 2977 uses the READ_VOUT register for current readback but the user must convert a millivolt reading to Amps or milliAmps.  The other big advantage is the OverCurrent fault detection and shut down ability of the 74/75 parts.  When a 2977 odd ch is configured to measure current, you give up all other resources on that channel, so you wont be able to use VOUT_EN or DAC pins, and fault detection is disabled.

    I hope this covers your questions. 

    Regards

    Mike

Reply
  • +1
    •  Analog Employees 
    on Apr 20, 2020 4:41 PM

    Hi Botnic, 

    If you plan to use 4 channels to monitor voltage and 4 channels to monitor current, I would recommend the LTC2974 or LTC2975. This is exactly the app that were designed for.  The difference between the 74 and 75 is the input supply current measurement capability of the 2975.  The 2974/75 and 2977 are the same with regards to servo/margining,sequencing, voltage sensing & measurement accuracy, OV/UV fault detection, and so forth.

    The big advantages of the 74/75 are the dedicated current sense pins and current related configuration registers that allow the user to program the Rsense value and readback registers are already converted to Amps.  READ_IOUT (74/75) accuracy is 0.3%, while the 2977 is current mode is 0.7%.  Accuracy in most cases is dominated by Rsense computed value vs actual sense resistance or DCR value for the inductor. The 2977 uses the READ_VOUT register for current readback but the user must convert a millivolt reading to Amps or milliAmps.  The other big advantage is the OverCurrent fault detection and shut down ability of the 74/75 parts.  When a 2977 odd ch is configured to measure current, you give up all other resources on that channel, so you wont be able to use VOUT_EN or DAC pins, and fault detection is disabled.

    I hope this covers your questions. 

    Regards

    Mike

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