I am looking for ESD protection diode for USB. I found TPD6E05U06 which is unidirectional TVS. Does this mean that protection is only over positive voltages ? and not for negative voltages ?
From the datasheet the DC breakdown voltage is 6.5 V. How this is related or differ then Reverse stand-off voltage and Clamp voltage.
Hi John,
The TPD6E05U06 will still offer protection over negative voltages, it will just begin conducting at a much lower voltage in the negative direction. This is illustrated below:
The reverse stand off voltage (VRWM) is defined as the maximum positive and negative voltage where current flowing through the diode does not exceed a certain amperage (typically 1nA). Once the voltage exceeds VRWM, it approaches the breakdown voltage (VBR), which is defined as the voltage where current through the diode exceeds a certain amperage (typically 1mA).
The clamping voltage is the voltage the protected IC will see during an ESD event. All ESD diodes have some small resistance, called the dynamic resistance (RDYN). RDYN will cause a voltage drop across a conducting diode; since the protected IC is in parallel, you will see that same voltage drop across the protected IC. This voltage drop is known as the clamping voltage.
USB signals only require uni-directional protection and in most cases it is preferrable since the uni-directional device will clamp at a lower voltage in the negative region than a bi-directional device. This will provide better protection for the protected USB ICs that are typically more sensitive to negative transients.
For more details on ESD diode specifications please see our ESD Fundamentals.
Regards,
Sebastian
