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TIDA-00366: Bootstrap circuit

M.A Amir
Prodigy 140 points
Part Number: TIDA-00366

Hello!

According to the schematic of TIDA-00366, at the starting point it's clear that bootstrap capacitors aren't charged.

So AMC1301 IC's used for three-phase current sensing are not supplied because their VDD1 are supplied from bootstrap circuit (VCC_U,VCC_V,VCC_W).

It is noted in AMC1301 datasheet that when VDD1 supply is missed, there is a fail safe output strategy that Vout-p goes to zero and Vout-n about 2.7v. The Amc output is Amplified with a gain of 0.797 through OPA320 and is summed with 1.65V which is (2.7*0.797+1.65=3.8v). so OPA output is saturated in 3V3.

therefore overcurrent protection comparator(TLC372) does it's duty and overload signal (output of TLC372) is produced making the nand-gate output to go high which is Disable signal.

Finally, Disable signal turns off the ucc21520. so the bootstrap circuit cannot be charged at all.

Am I right? this is what I am experiencing in my circuit. Is there any solution?

Thanks.

  • 0
    TI__Intellectual 2890 points

    Hello,

                 Thank you for looking into our TIDA-00366. Note that this design has provision to power the gate drivers with either external isolated supplies or internally using Bootstrap technique. Your analysis on overcurrent protection circuit getting active on power up with bootstrap technique is correct and this phenomenon will not occur while powered with external supplies. So in your design, you can modify the circuit such that MCU SW is disabling the gate drivers instead of HW. Alternatively you can add logic in the "overload" hardware path which will be enabled by MCU after power up sequence. Hope this clarifies.

    regards

    Navaneeth