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TIDA-00366: Bootstrap circuit

Part Number: TIDA-00366
Other Parts Discussed in Thread: AMC1301, OPA320, TLC372, UCC21520


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?