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TPS3803: Input clamp current parameter

Roberto Saba
Prodigy 80 points
Part Number: TPS3803
Other Parts Discussed in Thread: TPS3808E

Tool/software:

The TPS3803-01DCKR is characterized by the following parameter: Input clamp current, IIK (VI < 0 or VI > VDD) = ±10 mA.

But if I measure the existence of a diode between the SENSE and the VDD pins (i.e.: pins 5 and 4 respectively) I don't detect any diode.

I used the "Diode" function of a Fluke 179 multimeter, and I tried both the polarities: positive on SENSE and negative on VDD and positive on VDD and negative on SENSE. In both cases the multimeter showed "OL", taht is the indication showed when the tips are not connected at all.

I'd like to know the mechanism allowing this device to clamp the injected current.

Thank you in advance,

  • 0
    TI__Genius 9790 points

    Hello,

    Instead of simple diodes there is most likely more complex active circuitry that only triggers when the clamp current is exceeded. The exact circuit design is not available.

    Thanks,

    Walter

  • 0 in reply to Walter Zollinger
    Prodigy 80 points

    Thank you for your answer, but I'm not 100% satisfied. The real question is to verify if the device gets damaged in these functional conditions:

    • power supply (pin 4, VDD) = 1.8V
    • input (pin 5, SENSE) connected to GND through 10k and to +9V through 22k

    If a clamp diode with direct voltage = "Vd" = 0.3V was present, I would have said:

    • voltage on SENSE pin = VDD+Vd = 1.8V + 0.3V = 2.1V
    • current through 22k = (9V - 2.1V) / 22k = 314uA
    • current through 10k = 2.1V / 10k = 210uA
    • injected current = 314-210 = 104uA

    Since 104uA << Iik max. = 10mA, the device does not get damaged surely.

    But the diode is not present, so how can I be sure that the device is not damaged?

    Best regards.

  • 0 in reply to Roberto Saba
    TI__Genius 9790 points

    Hello,

    The device is designed so that it will not be damaged when operating within the data sheet specs. Exposing the sense pin to voltage greater than VDD+0.3V may damage the device. There appears to be an internal diode as the input limit is VDD+0.3V meaning an internal Schottky type. The diode may be unconnected until a clamping or ESD event and that is why it cannot be measured. 

    The new TPS3808E device has independent sense and VDD where Sense can be greater than VDD. VDD min is 1.7V so it could work with 1.8V.

    Thanks,

    Walter

  • 0 in reply to Walter Zollinger
    Prodigy 80 points

    I tested the device with power supply present:

    • power supply (pin 4, VDD) = 3.0V
    • input (pin 5, SENSE) connected to GND through 100k and to +28V (approx.) through 390k

    Voltage on pin 5 (SENSE) was 5.6V approx.

    It seems that there is no clamp effect at all (no Schottky diode activated on clampling event).

    So my original question remains: how can the TPS3803-01DCKR be characterized by a IIK (VI < 0 or VI > VDD) = ±10 mA parameter?

    Best regards

  • 0 in reply to Roberto Saba
    TI__Mastermind 18071 points

    Hi Roberto - We will respond by June 3rd. Thanks.

  • 0 in reply to Roberto Saba
    TI__Genius 9790 points

    Hello Roberto,

    Exceeding 10mA when VI < 0 or VI > VDD will cause damage to the device. Exceeding the recommended operating conditions of VDD=0.3V may decrease the reliability of the device. I suggest switching to 

    TPS3808EG01DBVR

    Thanks

  • 0 in reply to Walter Zollinger
    Prodigy 80 points

    If I connect SENSE to +28V through a 390k resistor, max. injected current is not more than 28V/390k = 72uA, then Iik cannot be exceeded, let's forget this problem. A problem could arise if the device does not clamp to VDD these 72uA, because the voltage on the SENSE pin would raise up to 28V, which is a value exceeding the max. allowed voltage. This is why I tried to know if the device has an internal clamp. If yes, the voltage would not raise above VDD+0.3V, and the reliability of the device would not be decreased. Since it seems that the device has not any clamping effect, I'm forced to add an external clamping diode to VDD to protect the device against overvoltage.

    We have thousands of TPS3803-01DCKR in house, so we're not willing to use a new device.

    Regards.

  • +1 in reply to Roberto Saba
    TI__Genius 9790 points

    For reliability I would suggest adding an external clamp.

    Thanks