• State Resolved
  • Locked Locked
  • Replies 7 replies
  • Subscribers 33 subscribers
  • Views 947 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

C/Q pin open

Bon Hsu
Prodigy 100 points

Hi,

I have a question about the device performance when C/Q pin is opened. We will use this device possibly under surge or/and transient in some period of time. But, the C/Q pin will be opened. I saw the comment at table 2 in the data sheet to describe this situation, and it is said failsafe output high. If under surge or/and transient, does it mean that the device might have false output high? Or, the output will be unpredictable?

Thanks, Best rgds,

Bon 

  • 0
    TI__Guru 62920 points
    Hi Bon,

    You are referring to the HVD101/102 family of devices, right? If so, the "failsafe high" state that is mentioned in the receiver function table of the datasheet just indicated that if there is no external connection at all to C/Q, the C/Q pin voltage will drift below the low-level input threshold due to leakage currents. This results in a high level on the receiver output pin. These leakages are relatively weak, so there might be potential for noise coupling onto C/Q during transient testing which would then toggle the receiver output. An external pull-up or pull-down resistance would help reduce the severity of any noise coupling.

    Does that address your question? If you need any more info just let me know.

    Best regards,
    Max
  • 0 in reply to Miguel Robertson
    Prodigy 100 points

    Hi Max,

    Thanks, the best way to avoid false trigger is to connect C/Q pin at GND while input is low and at Vdd while input is high as normal receive mode. Right?

    Best rgds, Bon

  • 0 in reply to Bon Hsu
    TI__Guru 62920 points
    Bon,

    Yes, that is right. The C/Q input thresholds scale with the L+ voltage, though, so it would be better to pull C/Q up to L+ rather than VDD. Note that if you directly tie C/Q to either L+ or GND it will prevent the transmit mode from working properly. Instead, some resistance needs to be used to limit the current C/Q needs to source or sink when driving the output.

    Max
  • 0 in reply to Miguel Robertson
    Prodigy 100 points
    Hi Max,

    In your recommendation, to limit C/Q current is to connect resistor Rset, or resistors between C/Q and L+ and L-? I think it should be resistor Rset.

    Could you please confirm it?
    Best rgds, Bon
  • 0 in reply to Bon Hsu
    TI__Guru 62920 points
    Bon,

    The Rset resistance sets the output current limit. What I meant is that in order for the C/Q output to be able to drive high and low during normal transmit mode (EN pin high), you shouldn't directly short C/Q to GND or L+. Instead, you should connect it to these voltages using a series resistance. If, for example, you shorted C/Q to ground it would make it difficult for the C/Q pin to ever transmit or receive a high level. (The driving device would output the maximum current for which it is configured, but the low-resistance short would make it so that the C/Q voltage does not increase much beyond 0 V.) A series resistance would allow the C/Q voltage to be either high (close to L+) or low (close to GND) without requiring excess current.

    Max
  • 0 in reply to Miguel Robertson
    Prodigy 100 points
    Hi Max,

    Do you mean if the differential voltage between L+ and L- is 32 V, it is better to parallel 71 ~ 320 ohm with TVS or MOV at L+ and CQ or L- and CQ due to the CQ output limit 100mA to 450mA?

    If you are confused about what I said, You can called me at 469-235-3091 or email me at chung.p.hsu@us.abb.com. Or, I can call you at Forest Lane office by phone number 214-567-XXXX

    Thanks,
    Best rgds,
    Bon
  • 0 in reply to Bon Hsu
    TI__Guru 62920 points
    Hi Bon,

    Sorry I didn't get to this today, but I can give you a call tomorrow to discuss.

    Regards,
    Max