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TRS3243E: Capacitor rating of C1-C4

Shota Mago
Expert 8130 points
Part Number: TRS3243E

Hi team,

My customer considers to use TRS3243EIRHBR and he is asking some questions.

  1. Is >10V rating of capacitor for C1-C4 enough?
    Though the datasheet states that abs rating of V+/V- is ±7V, there is no description about max voltage of C1pin and C2pin.
  2. The datasheet states that "Test conditions are C1–C4 = 0.1 μF at VCC = 3.3 V ± 0.3 V; C1 = 0.047 μF, C2–C4 = 0.33 μF at VCC = 5 V ± 0.5 V".
    What if each C1-C4 has greater than these capacitance(e.g. 1uF)?
    Is there any concern for rise/fall time of signal?
    Of course, the customer will use recommended capacitance, but he would like to make sure if a little bit bigger capacitance is okay or not in case shortage of capacitor.

Best regards,

Shota Mago

  • +1
    TI__Mastermind 47908 points

    Hi Shota Mago,

    Sorry for the late reply. 

    (1)

    Abs. max conditions rate the V+ and V- output voltages at +7V and -7V respectively. >10V rating for capacitors for C1-C4 would be enough, although I think doubling the voltage is more ideal allowing for more headroom. >10V rating will work for C1pin and C2pin as well. 

    (2)

    Depending on which capacitors are larger, this will affect the properties of the charge pump circuitry. This document that I linked below describes the charge pump technology, and the affects of C1-C4 when you alter their capacitances. 

    https://e2e.ti.com/blogs_/b/analogwire/posts/how-the-rs-232-transceiver-s-regulated-charge-pump-circuitry-works

    Capacitive values affect the voltage level of each ripple, as well as the frequency. Larger ripples take longer to discharge, and therefore the frequency is less. Smaller ripples take less time to discharge, which increases the frequency. The attached document goes into more detail about this type of architecture for our RS232 devices. 

    Regards,

    Tyler

  • 0 in reply to Tyler Townsend
    TI__Expert 8130 points

    Hi Tyler,

    Thank you so much for detailed explanation.

    Best regards,

    Shota Mgo