Hi,
Yes, basically it behaves like a simple zener diode.
I agree they act like zeners .... indeed.
But the OP asked:
Does this mean that protection is only over positive voltages ? and not for negative voltages ?
This can not be answerd with a YES.
It acts like a zener, thus it also protects against negative voltages.
***
* the functional block diagram is rather clear ... and usually does not need much explanation, if one knows how a diode and a zener works.
* 7.4 says: "The TPDxE05U06 is a passive integrated circuit that triggers when voltages are
above VBR or
below the lower diodes Vf (–0.6 V). "
* Figure 6-1 clearly shows protection (current) at negative voltage and positive voltage. Very steep V/I
***
The datasheet says "The TPDxE05U06 is a family of unidirectional Transient Voltage Suppressor ".
As non native English speaker - I find this expression somehow misleading.
For me it sounds like the "protection" is unidirectional (like the protection only works in one direction)
But instead the nominal (signal) working voltage is unipolar. (0V ... +5V)
So this protection device is good for signal voltage os 0..5V for example.
They are
not good for RS232, because RS232 signals are positive as well as negative w.r.t GND.
And they are not good for RS485 receiver side: While the transmitter sends out signals usually 0V...5V w.r.t. transmitter_GND ... there is an allowed GND_biounce between Transmitter and receiver of +/-7V, making the valid input voltage at the receiver side: -7V ... +12V w.r.t receiver_GND.
***
So each applicaition has it´s requirements. Choose the protection device according these requirements.
Or look at the datasheet and check if they are designed for your application:
Like here the datasheet, page1, "2 Applications" lists:
• HDMI 1.4b
• HDMI 2.0
• USB 3.0
• MHL
• LVDS interfaces
• DisplayPort
• PCI-express®
• eSata interfaces
• V-by-One® HS
Klaus