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ALM2402F-Q1: How to protect against shorts to battery voltage?

Part Number: ALM2402F-Q1

Greetings everyone,
i have an resolver application where shorts to an Battery Voltage is possible. I would like to know how one can protect the ALM2402F-Q1 against shorts to an e.g. 30V Battery Voltage (low impedance, high current) in the given non-inverting configuration without largely affecting phase and stability and also preserve full Output Voltage swing in Normal Operation.

with best regards,

Chris

  • Hi Chris,

    Below is the current-limit and short-circuit protection specification for ALM2402F-Q1. This is the current protection on ALM2402F-Q1 only. The resolver will not perform normal operation, since the Op Amp's output voltage is railed to 30V when the short is occurred. 

    I am enclosing the ALM2402F-Q1 User Guide. If seems that your Vs rail is a bit low for automotive application. The minimum Vs for single rail is 4.5Vdc. Your circuit has a gain of 1.25V/V.

    https://www.ti.com/lit/ug/sbou227/sbou227.pdf?ts=1594650094830&ref_url=https%253A%252F%252Fwww.ti.com%252Fsitesearch%252Fdocs%252Funiversalsearch.tsp%253FsearchTerm%253DALM2402F-Q1%2BApplication%2Bnote

    Best,

    Raymond

  • Hi Raymond,

    thank you for your Reply. During the short to 30V only protection is required.

    The Datasheet states that the current limitation does not take effect if the votlage is greater then the supply voltage, so damage to the device is possible

    Furthermore the Datasheets states that the maximum voltage at the input pins is 18V although the Input voltage is internally clamped at 7V with a 10k internal resistor.

    So my main concerns are the protection of the ALM2402F.

    Best regards,

    Chris

  • Hi Chris,

    I would place a zener at the each output of ALM2402FQ1's output stages, to clamp the potential short between Op Amp's Vouts to 30V (Vbatt rail).  Since your Vcc rail is only 7Vdc, the rated zener voltage may be 9-12Vdc will be sufficient. 

    If there is such short, I am not certain about your statement "without largely affecting phase and stability and also preserve full Output Voltage swing in Normal Operation.". The resolver's winding will likely have high DC resistance than 0.1Ohm (Vattery's impedance < 0.1mOhm). it will create the AC short on the branch that is shorted to Vbattery. The non-shorted branch on the opposite side of the excitation transformer may still work, but the sine balances part of output excitation voltage will be skewed. So it will affect the normal operation. 

    Best,

    Raymond

  • Hi Chris,

    We haven't heard from you in a while. We hope the issue was resolved. I am going to close thing thread now, please reply to reopen if you have any additional questions / information.