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TS12A12511: About Input protection diode and COM pin absolute maximum rating

Tsukui Yusuke
Guru 21930 points
Part Number: TS12A12511

Hi,

Customer created a system using TS12A12511 with input switching.
They are using TS12A12511 under Vcc = 5V, -Vcc = 4.5V conditions.
When connecting a signal to this set, a transient voltage below -Vcc is applied temporarily.
Let me ask you three questions about negative voltage transients.

１．
Data sheet states that the absolute maximum rating of the voltage applied to NC, NO, or COM is -Vcc-0.5V.
From this specification, it is presumed that an ESD protection diode is provided between the NC, NO, or COM terminals and -Vcc.
However, when observing the input signal waveform, the voltage is not clipped to -Vcc-0.7V.
Is there a protection diode?

２．
If a protection diode is installed,
Maximum input current II / O specified by the absolute maximum rating in the data sheet is Continuous current NC, NO, or COM ± 50 mA.
Will the device be damaged even if ± 50mA is constantly generated in the protection diode?
In addition, there is Peak current NC, NO, or COM ± 100 mA, but momentarily, it will not break even if 100 mA flows.
Is this understanding correct?
Also, how long do you expect the duration time of the peak current?

３．
On the other hand, from the viewpoint of voltage, a transient of -8V is generated.
Is there a time limit for voltage transients?
Please let me know if there are any of the following rules.


Best regards.
Yusuke

  • 0
    Guru 244350 points

    1. There are protection diodes, but they are designed only to handle ESD events. A large current will result in a large forward voltage.

    2. The continuous and pulse specifications describe the current that flows through the switch during normal operation. The diode current is not specified. The actual limit is probably smaller than 50 mA.

    3. The diodes are guaranteed to handle ESD tests as specified in JS-001 and JESD22-C101. If your transient has more energy, then it might fry the diode.

    Would it be possible to insert a series resistor that limits the current to something like 50 µA?

  • +1
    TI__Mastermind 43676 points

    Hi Yusuke,

    1. Clemens is Correct - they are ESD diodes so a larger current can result in a large forward diode drop.

    2. Clemens is also correct here - the +/-50mA is for switch current (current through the MOSFET switch not ESD diode current - it isn't spec'd but it will be <50mA - so continuous diode current of 50mA could damage the device. 

    3. This device is not rated for voltage transients above VCC or below -VCC beyond what is tested in the ESD specs (JS-001 and JESD22-C101). Using a series limiting resistor to keep voltage with VCC + 0.5V to -VCC -0.5V and the current low. If stronger clamping is necessary a series resistor and an external TVS diode should be applied to the system to protect the IC - as its not really designed for voltage transients and with the voltage range you are using this is one of the better parts for those applications - so I'd suggest adding external protection to protect the IC from the transients in the system.

    If you have any other questions please let me know!

    Best,

    Parker Dodson