Failing ESD Immunity test where TI's TIPD126 design passes - Page 1
Forum section: electronics / projects

author: yashrk
author_rank: Frequent Contributor
timestamp: November 21, 2020, 11:14:50 am
content: Hey everyone,I am using XTR117 in transmitter product by referring TI's CerTIfied design TIPD126.We have used same component as shown in the TI's design but we were failing the ESD immunity test. We are going for 8kV contact discharge and 15kV air discharge. We have aluminum enclosure with cut out for LCD display, membrane keypad and external 4-20mA 24V input connector. There is aluminum sensor body attached on the back of the case and sensor wire running the internally to the sensor body and in to the enclosure.We tested the device with and without protective earth in both case the device failed damaging the XTR117 when disconnected from protective earth LCD was also damaged. When protective earth was connected (also checked that the case's both half and sensor body are connected to earth) no other component was damage apart from XTR117.As the sensor body and case were connected to earth we hadn't provided any ESD protection devices.Final device will be used without protective earth.Q1. Please suggest techniques for ESD protection?Other concern we have is. When there is ESD event occurs and TVS diode will short it to local GND which is not the supply GND or Earth but the 'local GND' which is connected to the 'supply GND' via XTR117's 25ohm internal resistor.Q2. Even after adding the requisite protection (TVS diodes) to the exposed pins will the XTR117 survive the ESD current surge on its Iret pin? Is there anyway to protect the IC?

author: Elasia
author_rank: Frequent Contributor
timestamp: November 21, 2020, 01:35:02 pm
content: TVS to supply ground and look at using ESD rated MLCCs sent to supply ground and ferrites on the inputsAlso look at having a TVS be at right at the supply power.. you shouldnt be shunting your ESD pulse back into your chip / circuits

author: jkostb
author_rank: Regular Contributor
timestamp: November 21, 2020, 02:29:27 pm
content: I have used the XTR117 successfullly in different products and all passed successfully the ESD test. The fact that your design fails the ESD test is caused by the board layout and grounding strategy. For ESD and surge you need to clamp the overvoltage by using TVS diode. But this alone is certainly not sufficient. You need to divert the peak surge currents to some reference metal plane. Otherwise it will flow through your electronics and damage your IC's. So you need to ensure that the surge currents are diverted to your aluminium housing.Please note that these ESD surge currents are high frequent (200-400Mhz). So you need to ensure that your electronics ground is bonded to the chassis and have low impedance for high frequencies. If your electronics must be isolated then you can use capacitors to create a low impedance connection between electronics ground and chassis. Please note that the PE connection as already discovered will not protect the XTR117 because the wiring has too much inductance. You can only protect your electronics by providing a path to chassis which has low impedance.