TPS1HB08-Q1: How much current capability of VBB clamp diode is ?

Hi Yoshiki, 

The image that comes on the datasheet is not showing an application in which you would be using a resistance to limit the ESD event. This image shows an standardized transients test ISO7637 in which this impedance must be lower than 50ohms. This impedance would not be placed on an application since it would be in your main power path and will dissipate power and drop your voltage. 

These voltage clamp diodes are rated for very specific ESD events that are included on the datasheet. The following table can be found on the datasheet and refers the specific event that the clamp diodes are rated for. 

Note that the diodes are only rated for the ESD events specified on the datasheet. If you apply any event not rated for in the datasheet, these diodes will not protect the system. In case of using other transients events, your would need to include a TVS or other type of protective device. 

Hi Yoshiki, 

Let me know if you have further questions here.