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TIDA-01333: Rshunt rating

AJ
Intellectual 570 points
Part Number: TIDA-01333
Other Parts Discussed in Thread: TVS2700

Hello TI Support,

I was reviewing TIDA-01333 front end, and got the following questions

#1 What is the maximum VIN rated for (continuous)?
#2 How is the input protected against electrical fault (Non ESD/transient related) in the event TLP3123 is ON and VIN > 10V?

if my math is correct, for VIN = 10V, R30 (0.125W) is under-rated and should be at least 0.25W assuming 20% margin. 

The reason I ask is that, I am designing a similar front end.
In my case VIN_MAX = 24V, and I am thinking to add PTC to limit current in case of fault and allow for smaller sized resistor

without a PTC similar to circuit in the diagram above

  • power rating for 100E / 200R are 0.75W / 1.5W respectively.

with a PTC (Itrip = 60mA)

  • power rating for 100E / 200R are 0.4W / 0.75W respectively.

I came across the TVS2700 (Vclamp = 32.5V typical), but I am not sure what to make up of the DC breakdown current IBR = 12mA

#3 Does this IBR rating means that the maximum current should be limited to 12mA DC when the device is fully ON?

Thank you,
AJ

  • 0
    TI__Expert 3500 points

    Hello AJ,

    - first I couldn't see the schematic snippet you put here in TIDA-01333 schematic. so I will consider the circuit here for my answe.

    - in the case of input reaching 10V, R30/R29 will divide it and R30 should get maximum 6.67V, so your calculation for 0.25W seems right to me. I think this fault case is not considered in the design.

    - PTC is considered a standard method to protect 4-20mA current input, majority of modules have a maximum of 30mA as limit. so if PTC of a trip current above 30mA and below 60mA is used, that would lead to a lower rating required. and transient pulse power till the PTC trips should be considered and handled by the burden resistor chosen.

    - IBR: DC break down current represents the minimum current required for break down. two conditions are required for breakdown to occur: breakdown voltage is achieved, and voltage source is capable of delivering the minimum current. in TVS2700, a VBR voltage of 29.3 to 33.9V is reached, and its source is capable of delivering 12mA at least. if the source is not capable, no breakdown occurs.

    when the TVS device is in breakdown, it can pass current limited only by its power rating, peak current (Ipp) of TVS2700 in case of surge event is 40A (page 3/DS)

    - I do recommend to reach out to your sales/field support engineer, as TI is offering very soon a semiconductor solution to your exact problem, a device that will protect the burden resistor, without the need to raise its rating. the device will have a voltage/current limit, so it will switch off if either limit is reached.

    Best Regards,

    Ahmed

  • 0 in reply to Ahmed Noeman
    Intellectual 570 points

    Hello Ahmed,

    Thank you for taking the time to answer and clarify.

    Will definitely reach out! Thanks for the helpful information :-)

    Best,
    AJ