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TPS40090: How to use CT to measure peak current for Vout = 24V?

Sam Guo
Intellectual 380 points
Part Number: TPS40090

Since the current amplifier Vcom(max)=4V.  I want to use Current Transformer, not DCR.  I have questions:

1.  How to make the connection?  The block diagram does not show the current amplifier details.

2.  What is the maximum Vct(peak) to the input pin?

3.  Vct is not of triangle wave.  Is it OK?

4.  What is the function of the internal differential amplifier internally?   I see it is not connected to anywhere.  If I want to use it externally, shall I add 4 matched resistors?  Why its gain is 1?

5. In my last email, I asked slope compensation.  Forget this question because I do not need it due to  D < 40%  

Please let me know the answer quickly.  My design time is tight.  Thank you.

Sam

  • 0
    TI__Mastermind 24075 points

    Hi Sam,

    1. The current transformer can only sense AC current, not DC current. So it can not be used to sense inductor current.

    The below circuit can be used to reduce Vcom of current sense amplifer. R1 to R4 should be 0.1% tolerance resistor to reduce the error induced by resistor divider. R5 is used to limit the charging and discharging current through C1, hence to reduce the voltage ripple on CSCN. R5 value is 5 to 10 times of R1//R3.

    2. Remote sense amplifier is used to sense the voltage at remote side (load side), so the controller can regulator the voltage at load side tightly.

    As Vout is high voltage (24V) in your application, remote sense amplifier can not be used. Connect TPS40090 VOUT and GNDS pins to ground, leave DIFFO pin open.

    Btw, I will send a message with my email. Let's discuss by email for convenience.

    Thanks

    Qian