LM5066: Current monitor and soft start question

Part Number: LM5066

Hi Team,

I have three questions about current monitor and soft start question, could you help me?

1. In LM5066 datasheet it have accuracy when VIN-SENSE voltage = 50mV and =25mV, for lower voltage across shunt will have higher tolerance and we didn't have clear spec correct? Ex. CL connect to GND and 10mV tolerance will > 3% but didn't have spec. 

2. If didn't reserve soft start circuit, is LM5066 have other way to adjust start-up slew rate?

3. May I know the reason why at lower voltage across Rshunt condition will have worse current monitor accuracy?

Best Regards,

Roy

  • Part Number: LM5066

    Hi Team,

    Sorry that I would like to edit it but it looks like have some problem, so I update my questions as below.

    I have four questions about current monitor and soft start question, could you help me?

    1. In LM5066 datasheet it have accuracy when VIN-SENSE voltage = 50mV and =25mV, for lower voltage across shunt will have higher tolerance and we didn't have clear spec correct? Ex. CL connect to GND and 10mV tolerance will > 3% but didn't have spec. 

    2. If didn't reserve soft start circuit, is LM5066 have other way to reduce the inrush current?

    3. May I know the reason why at lower voltage across Rshunt condition will have worse current monitor accuracy?

    4. If change to LM5066I will have significant better at light load current monitor tolerance? Or at light load(V across rshunt <15mV) condition current monitor tolerance will still very high and didn't have a clear spec, just a little bit better compared with LM5066? 

    Best Regards,

    Roy

  • Hi Roy,

    1A) We have only two thresholds (25mV and 50mV) possible with this device which can be selectable based on CL pin connection.

    2A) you can set lower power limit threshold to reduce the inrush current

    3A) At lower current, the signal available is of low magnitude. So, the offset voltage becomes dominant and hence power accuracy

    4a) We can get slightly better accuracy with LM5066i than LM5066

    Best Regards

    Rakesh

  • Hi Rakesh,

    1) Sorry that maybe I didn't express clearly, my question would be if CL connect to GND (set 50mV threshold), and in datasheet it have the input current monitor spec at VIN-SENSE=50mV condition that +-3%, may I know if CL connect to GND, but VIN-SENSE lower than 50mV, for example: 10mV, at this condition input current monitor accuracy will be higher than +-3% correct?

    And if the VIN-SENSE voltage lower, the input current ,monitor accuracy will be higher than +-3% correct?     

    2) Is the LM5066 register D1h means the voltage across shunt resistor or the value after below formula translated?

     

    3) Will the sense resistor divider circuit help to increase current monitor accuracy significantly at low voltage across shunt(<10mV) condition? For example: from 30% become 15%, or it's help higher voltage across shunt condition more? 

    Best Regards,

    Roy

  • Hi Roy,

    Please see the below responses in the order of your queries.

    1) Correct,

    2) D1h register provides input current information, if the following coefficients are used. 

    3) The sense resistor divider circuit will not help to increase current monitor accuracy significantly at low voltage across shunt(<10mV) condition.

  • Hi Avishek,

    Thanks for your feedback, and if I would like to increase input current limit accuracy so I increase shunt resistor(from 2m ohm to 10m ohm, also set OCP as 5A, system will operating at 4.2A maximum) to make VIN-VSENSE higher at same input current condition compared with original shunt resistor value(2m ohm), but LM5066 in my system will trigger current limit then turn off during power on, if the LM5066 output cap can not decrease and didn't have dvdt start-up circuit at gate pin, is there any solution can make the system turn on successfully and keep shunt resistor as 10m ohm except for increase CTIMER?

    Best Regards,

    Roy 

  • Please fill out the design calculator and share with me to answer to your questions.

    https://www.ti.com/tool/download/SNVU080 

  • Hi Avishek,

    Ok, please allow me 1-2 day fill in it since I am fully occupying by other case, after I finish I will upload.

    Best Regards,

    Roy