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CD4000 ESD Diodes

In case anyone was wondering, the input-pin-to-GND diode has excellent hFE:

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Measured on CD40106BE with all input pins in parallel. The parasitic BJT is an NPN from input (emitter) to VSS (base) to VDD (collector).

So, if you use the input ESD diodes to clamp a negative-going signal, the clamp current is essentially cascoded into VDD. Expect a proportional increase in supply current!

This BJT in turn forms an SCR with nearby P wells. hFE depends on Vce, so it doesn't latch up when fully saturating into a 60 ohm load resistor, but latches above about 80mA with Vce = 10V. Latchup current is around 280mA for this part.

Analogously, the input-VDD diodes also have hFE (PNP from input (emitter) to VDD (base) to VSS (collector)), but it's small, about 0.5.

HEF4011BP shows a little crosstalk between input pins within a gate: hFE ~

0.035 (for the Vdd diodes; none for the Vss diodes). 74HC shows a similar effect. No crosstalk between gates.

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
Website: http://seventransistorlabs.com
Reply to
Tim Williams
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That?s nice indeed. I have never seen anybody doing the actual meas urements before, plenty of talk

I once reviewed a design in which a colleague of mine used the protection d iodes as a part of the design. It failed in both theory and practice

But, back to the Hfe. Do you actually dare to use this in an actual product ? (AFAIR the latchup current and/or hFe is not specified)

Cheers

Klaus

Reply to
Klaus Kragelund

Vitally important information for those still using antique devices in "modern" _production_ >:-} ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| STV, Queen Creek, AZ 85142    Skype: skypeanalog |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 

           To those of us in my age bracket... 

           GREEN means inexperienced and/or incompetent.
Reply to
Jim Thompson

easurements before, plenty of talk

n diodes as a part of the design. It failed in both theory and practice

uct? (AFAIR the latchup current and/or hFe is not specified)

I use lots of antiques. TRS sockets, ceramic caps, PCBs, PVC insulated flex , all sorts.

NT

Reply to
tabbypurr

Good engineering practice would ensure that the design limits clamping current wa-a-a-ay below latch-up specification... not only to protect against latch-up, but to minimize cross-talk: old chip designs do not have the modern-process deep-diffusion "walls" that keep ESD currents away from active circuitry. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| STV, Queen Creek, AZ 85142    Skype: skypeanalog |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 

           To those of us in my age bracket... 

           GREEN means inexperienced and/or incompetent.
Reply to
Jim Thompson

The design I was reviewing had no limitation at all, no resistor-schottky-resistor, but just clamped directly into the cmos pin by purpose

Reply to
Klaus Kragelund

The design I was reviewing had no resistor-schottky-resistor protection, but clamped into the cmos pin by purpose

Cheers

Klaus

Reply to
Klaus Kragelund

Not good. Ways to safely do that have been discussed here many times. ...Jim Thompson

-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

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| 1962 |

Spice is like a sports car... Performance only as good as the person behind the wheel.

Reply to
Jim Thompson

I once used a cmos analog multiplexer *only* for its ESD diodes.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com
Reply to
John Larkin

I've only been involved in a few outright technical failures, and one was an alarm system for a tugboat where I figured that the inputs could be a series resistor straight into a CD4000 gate (an *A* series gate.)

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com
Reply to
John Larkin

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