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Original question:

TCA9617A: VCCA and VCCB connected to the same 3.3V together

TCA9617A: TCA9617A power sequence

Cai Jun
Prodigy 20 points

Part Number: TCA9617A
Other Parts Discussed in Thread: TCA9617B

Hi TI experts,

One question here: 

From TCA9617A datasheet, it states that: VCCB should always be higher than VCCA. VCCB cannot be lower than VCCA even when the device is disabled. During power-up, VCCB must rise before VCCA.

From previous ticket, we understand that we could apply the same power supply for VCCA and VCCB.

But how about the power sequence? Is there any harm if VCCA is powered up before VCCB?  If yes, what kind of harm it is? Reliability or functional failure? 

BR,

Jon

  • +1
    TI__Guru 55258 points

    Hi Jon,

    The main reason why we say to power up VCCB first before VCCA is due to the internal ESD diode structure that stems from VCCA to VCCB. Powering VCCA first can backbias into the B-side through the diode, thus we suggest VCCB be powered first. The diode I believe has a forward voltage of ~0.5V, so as soon as VCCA becomes greater than VCCB by 0.5V, then current would begin to backbias the B-side supply. 

    The TCA9617B version allows for A-side supply to be larger than B-side without any issues occurring. 

    Regards,

    Tyler 

  • 0 in reply to Tyler Townsend
    Prodigy 20 points

    Hi Tyler,

    Thx a lot for your quick response.

    We will check TCA9617B. 

    BR,

    Jon