Conformity Magazine - September 2008 - (Page 32)

Challenges in Pre-Pulse Voltage in the HBM ESD Model Testing by Robert Ashton, ON Semiconductor © Nikolai Sorokin | Dreamstime.com ynamic clamps have become very popular in the last few years for providing ESD robustness for integrated circuits. [1] They have a number of advantages which will be described below. Several years ago, a pattern emerged in the human body model (HBM) testing of dynamic clamp protected circuits. Circuits with moderate or high leakage were protected very well by dynamic clamps, but circuits with very low leakage would often fail at lower than expected values. It appeared that the dynamic circuits were not functioning as designed. Voltage measurements, prompted by the trailing pulse HBM simulator issues discovered by Texas Instruments, [2] revealed an unexpected voltage across the dynamic clamps before the HBM current pulse if the circuit leakage was vey low.[1] (Note: an HBM simulator is a test instrument that performs a simulated ESD event on an electronic component. It is not a computer program.) This article will explain the origin of this pre-pulse voltage (PPV), describe the working and advantages of dynamic clamps, explain how the PPV prevents operation of the 32 Conformity September 2008 dynamic clamp, relate how the PPV in an HBM simulator relates to real world ESD stress, discuss how the ESD standards have dealt with the PPV issue, and what concerns should remain about the PPV for ESD test engineers and ESD designers. PPV Origin The basic HBM schematic is shown in Figure 1. A 100pF capacitor is charged from a high voltage power supply, and a relay, S1, initiates the HBM stress pulse through a 1500Ω resistor to the device under test (DUT). The HBM current pulse has a 2 to 10 rise time and a 150ns exponential decay, assuming the DUT resistance is much less than 1500Ω, as illustrated in Figure 2. Figure 3 shows measurements of the PPV. The DUT has been replaced with a 10V Zener diode, and the voltage across the diode has been measured alone and with 1MΩ and 10kΩ resistors in parallel to simulate varying degrees of leakage, as illustrated in Figure 1. The HBM schematic does not suggest any voltage across the device before the current pulse. Relays, however, are not perfect circuit elements, and their physical properties will differ from an ideal switch. http://Dreamstime.com

Table of Contents Feed for the Digital Edition of Conformity Magazine - September 2008

Conformity Magazine - September 2008 Contents Editor’s Note Commission Adopts Regulations for Internet-Based TRS Services Another Company Fined for Non-Compliance with HAC Requirements FCC Extends “Do-Not-Call” Registry Compliance Requirements Marketing Company Gets $1.4 Million Fine for Junk Faxes EU Commission Codifies Directive on TTE Market Competition EU Commission Releases Updated Standards List for the R&TTE Directive Updated Standards List for the “New” Low Voltage Directive Released New Standards List Released for the EU’s Machinery Directive The ESD Association: Voluntary Standards in Action ESD Open Forum Medical EMC Standards: Towards the 4th Edition of IEC 60601-1-2 iNARTE Informer Pre-Pulse Voltage in the HBM ESD Model Digital Interfaces and EMC Performance ESD Design Buyer’s Guide Product News Commission Publishes Updated Standards List for the EU’s Personal Protective Equipment Directive FDA Links “Human Factors” to Adverse Events with Medical Devices CPSC Actions in the News IEC Standards Update UL Standards Update Product Reviews Telcordia Standards Update From Our “You Can’t Make This Stuff Up” Department Looking Back: Items from Past Issues of Conformity Advertisers

Conformity Magazine - September 2008

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.