ISO7821: ESD test issue

Guru 18205 points

Part Number: ISO7821

Hello

A static electricity test of 15 kV aerial discharge was conducted on a system using ISO 7821, and the phenomenon occurred that the VOL of OUTB of ISO 7821 became 2.5 V.
5 V is applied to Vdd 2.
When the power is turned on again, the VOL becomes 0 V without any problem.

What is the mechanism of VOL becoming 2.5 V?

Although 15 kV is not directly applied to ISO 7821, there is a possibility of wraparound.
Since the ESD rating of ISO7821 does not correspond to 15 kV, they are planning to take measures against static electricity.
Please tell me if there is a recommended countermeasure circuit.

Best Regards,
Ryuji Asaka