Do discrete MOSFET transistors contain ESD protection? - Page 1
Forum section: electronics / projects

author: zapta
author_rank: Super Contributor
timestamp: August 13, 2015, 03:14:40 am
content: Digital MOSFET ICS do contain ESD protection in form of clamping diodes.What about discrete transistors such as the one below? Do they also contain ESD protection? If so, does it effect the operation/model of the transistor (e.g. negative VGS is clamped)? If not, does it make them *terribly* sensitive to ESD?http://www.diodes.com/datasheets/ds31838.pdf

author: c4757p
author_rank: Super Contributor
timestamp: August 13, 2015, 03:33:42 am
content: Not unless they specify that they do. Most discrete MOSFETs areonlyMOSFETs. And yes, the gates are quite sensitive. That one specifies VGS(max)at +/- 8V; you're likely to punch straight through the gate oxide without much more than double that, or less if they were optimistic.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 13, 2015, 05:10:51 am
content: I've heard of breakdown more like 5x rating, but yeah, you can wheeze right by there with kV+ of ESD, no problemo.There are kinds with internal zeners, which are usually as small as possible, only good for a few kV HBM.FYI, not all digital ICs contain protection diodes (or enough of them to matter). I think CD4007 (essentially a MOSFET array) omits them.Tim

author: Marco
author_rank: Super Contributor
timestamp: August 13, 2015, 03:32:54 pm
content: I've seen some horror stories about the levels of care required to reliably assemble PCBs with 2n7002s, can't find the post now but he didn't get returns down to a decent level until he started wearing an ESD apron on top of the normal precautions.

author: Nerull
author_rank: Frequent Contributor
timestamp: August 13, 2015, 06:44:53 pm
content: I've worked on a product which consisted of a simple PID controller PWMing 4 logic-level mosfets to regulate temperature of a heating element. They had set up a spray booth to apply conformal coating to the boards, and hadn't used an ESD-safe curtain on the booth. Those mosfets failed closed circuit at an alarming rate.

author: nctnico
author_rank: Super Contributor
timestamp: August 13, 2015, 09:40:10 pm
content: IMHO it helps to put a 10k pull-down resistor on the gate of a MOSFET. That at least prevents building up a charge on the gate.

author: Christopher
author_rank: Frequent Contributor
timestamp: August 13, 2015, 09:59:02 pm
content: 10k at 12v is pissing away just over a milliamp.. I've used 100k to 1M before to keep the gate pulled lowThis won't do anything for esd though, will it

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 13, 2015, 10:08:57 pm
content: If anything, ESD might jump the resistor as a spark gap, but not after kV have been applied to the rest of the circuit. So, no. Bleeders or pull-downs/ups are good practice anyway, and typically required for function (you don't want floating connections, ever).Tim

author: zapta
author_rank: Super Contributor
timestamp: August 14, 2015, 01:17:38 am
content: Quote from: T3sl4co1l on August 13, 2015, 10:08:57 pmIf the gate is driven directly by an MCU, does the protection diodes of the MCU also protect Vgs ?

author: Circlotron
author_rank: Super Contributor
timestamp: August 14, 2015, 01:19:42 am
content: I did some tests on about five 600V 3 ohm TO-220 mosfets about 15 years ago. The gates would pop at around 45vdc.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 14, 2015, 05:22:48 am
content: Quote from: zapta on August 14, 2015, 01:17:38 amIf they are close by, and there's no series resistor, perhaps. But why are you having ESD exposed to an internal trace?Tim

author: juanfermed
author_rank: Regular Contributor
timestamp: September 15, 2015, 03:31:57 am
content: As c4757p, they do not contain any ESD protection unless it is stated. And even when stated, it does not mean the ESD protection is suitable for your real world application.For example, some ICs and MOSFETs stated a HBM -Human Body Model- and CDM "Charged Device Model" in the range of 400 - 2.5kV. These parameters imply mostly only that the device can/will survive assembly during production be it on its own assembly line or your final production assembly line (if the assembly line complies with proper ESD regulations).If a device is ESD protected or provides any kind of ESD protection for the real world, it will for sure state it and even use it as advertising, since its a feature that not all devices have. The reason for this is that good ESD protection usually requires more silicon and thus area, making it more expensive. A person can rise a charge of up to 35kV just by walking on a carpet.Dont be confused in the MCU datasheets when it states "I/O lines ESD protected" as it might only imply that I/O lines are protected for production ESD levels, and not real world. I might be wrong, but a device has ESD protection designed for real world when it is fully characterized in the datasheet.Please refer to the following documents and links for more details:http://powerelectronics.com/regulators/selecting-protection-devices-tvs-diodes-vs-metal-oxide-varistorshttps://www.esda.org/about-esd/esd-fundamentals/part-1-an-introduction-to-esd/

author: zapta
author_rank: Super Contributor
timestamp: September 15, 2015, 04:11:38 am
content: Quote from: juanfermed on September 15, 2015, 03:31:57 amI should have clarified that, my question was about handling the part before assembly, not operation in the field.