EL7900

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Jim hasn't been paying attention. Marco Trapanese has already done that, and told us about it.

Using his original 3.3V supply, the output went up to 2.7mA with increasing light levels before collapsing on further increase. When he raised the supply close to the absolute maximum 5.5V, the output made it to 3.5mA before collapsing, well below the 6mA mentioned in the data sheet.

-- Bill Sloman, Nijmegen

Crank Vcc up to +5V and re-test. ...Jim Thompson

You could easily have done without the first sentence of your reply. That would have moved your position from "fatheaded jerk" to "helpful."

Enjoy your retirement.

Aha! It finally dawns after staring at the data sheet forever!

Where are you measuring the current?? ...Jim Thompson

For some reason, of which I can't quite put my finger on, my guess is the enable device is running out of Idss.

The OP should define his set-up more accurately... right now, nothing computes. ...Jim Thompson

I think the part is defective and the data sheet is a pack of lies. It mentions "direct sunlight" and "output saturation" as if the foldback mechanism doesn't exist. Fig 9 is an outright attempt to hide the foldback. Their "Short circuit current limit" section is absurd.

It's common for data sheets to deliberately avoid documenting regimes where parts screw up.

Google this, world: Intersil EL7900 has bad bugs

Somebody should start and maintain an IC bugs web site.

I think their enable concept is failing... can't support the load. The mirror, alone, would saturate, but not collapse. ...Jim Thompson

The PD doesn't behave like a normal current source--once the bias collapses, it'll pull below ground. That will probably do things the chip doesn't like, and will make it pretty hard for the mirror FET to do anything useful.

Cheers

Phil Hobbs

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I believe what John is saying that the schematic explains why it will happen, but not why it happens at a much lower current than it should be able to output according to the datasheet

-Lasse

It took Intersil a few tries to get their ALS products right. The newer digital ones are much better. Look at the spectral sensitivity curve in the DS for the case with no IR absorbing glass--it has a _huge_ IR response that will make it badly wrong under incandescent light.

Also, of course, full zenith sunlight is about 100k lux, not 8000.

Cheers

Phil Hobbs

Oooh, interesting. Optically-pumped sneaky substrate currents, without even needing a negative power supply!

I've been exposed to your posting habits for too long, and in any event this is the same Jim Thompson who claims to have reported me to the FBI for having dangerously anti-American ideas. His other imbecilities need to be advertised - people might otherwise take him seriously

Really? Jim Thompson is the fat-headed jerk around here - and I'm one of the people who's had more than enough of his silly ideas. Giving him a hard time doesn't make me either fatheaded or a jerk.

And who would I having been helping when I pointed out something that would have been obvious to anybody who'd actually followed the thread?

I can think of better things to do with it than correcting narcissist jerks like you, but I've haven't been able to make any of them work yet.

-- Bill Sloman, Nijmegen

It's a FEATURE ;-) ...Jim Thompson

But it can't pull current below about -0.7V, right? ...Jim Thompson

Il 30/08/2012 17:00, Bill Sloman ha scritto:

"High intensities"... just a desktop lamp! Or the led of my smartphone.

Marco

At a guess, I'd say that it probably won't pull much below -0.55, maybe

-0.6--there won't be much photocurrent coming from that little die.

Cheers

Phil Hobbs

Il 30/08/2012 18:20, Jim Thompson ha scritto:

What other information should I provide? Even if the actual board has a chain of 74HC595 to enable one EL7900 at time, the tests I reported was conducted with only one sensor soldered on an empty PCB.

Vsupply: 3.3V (and 5V as described) Enable: tied to GND Rload: 562 ohm (I tried other values)

I think such a setup should be very close to the one the Intersil's guys used to characterize the pd.

I use a desktop lamp to illuminate the sensor and I have both a voltmeter and a ammeter to measure the output current and the voltage across the Rload.

Marco

Il 30/08/2012 18:01, Jim Thompson ha scritto:

A whole batch, indeed. I have bought 1000 pcs and they all have this behavior.

I'm sorry I've already written about this. At 5V it collapses around 3.5-3.6 mA.

Marco

Il 30/08/2012 18:09, Jim Thompson ha scritto:

I apologize. I cannot understand the meaning of your sentence. It's my fault, English is not my primary language.

Between the pin "output" of EL7900 and one end of the rload. The other end is tied to gnd.

Marco