Dear Analog Devices Support Team,
My name is Duy, from the datasheet of LTC2975 and PMBus specification, it seems there are two methods to read the output current:
- READ_IOUT
According to the datasheet, the READ_IOUT command returns the ADC measured differential current sense voltage (ISENSEPn – ISENSEMn), with a resolution of 400 µV/LSB (see page 7 of LTC2975 datasheet). With my Rshunt = 1 mΩ, this results in approximately 0.4 A/LSB, which seems relatively coarse for my application.
Question 1.1: Is there any recommended way to improve current sense resolution without changing the shunt resistor and without external Amplifier (e.g., configuration options, scaling adjustments, or alternative measurement modes in LTC2975)?
Question 1.2: I noticed that the LTC2974 provides adjustable ADC input ranges (Vin_ADC) to improve resolution (see page 5 of LTC2974 datasheet), but I could not find similar functionality in the LTC2975 datasheet. Could you please confirm whether the LTC2975 supports such adjustable ranges?
If my application requires Vin_ADC = 16 mV for better resolution, should I consider using LTC2974 instead of LTC2975?
- MFR_READ_IOUT (0xBB)
Question 2.1: Can the MFR_READ_IOUT command be considered the preferred method to improve effective resolution in practical applications, compared to using READ_IOUT?
Question 2.2: Does the ADC always measure the differential voltage between ISENSEPn and ISENSEMn for both READ_IOUT and MFR_READ_IOUT? Is the difference between these two commands only the scaling/format (linear vs fixed 2.5 mA/LSB), while the underlying ADC measurement comes from the same sense pins?
Question 2.3: For example, if Iout = 4 A and Rshunt = 1 mΩ, then
b[15:0] = 4 A / 2.5 mA = 1600 (decimal) = 0x0640.
Is it correct that this result does not depend on the Rshunt value after calibration?
Thank you very much for your clarification.
Best regards,
Duy Nguyen