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What's the hi-side current sense chip du jour?

Hello,

-> Attention, non-political post ;-)

Buck converter chips should contain high-side current sensing to be able to precisely limit the output current regardless of the input voltage level. But they typically don't, for whatever reason . The INA193 and its brethren are nice for sensing but pricey:

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Then there is the simpler transistor array chip solution for less dough, devices such as the ZDS1009:

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or for under a buck:

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The latter two are marginal in abs max across the sense terminals, in case of a big fat bzzzt ... *WHADDABANG* type of short, wrench falling onto the rail and such.

Any other parts out there that are a bit more jelly-bean? Ok, ok, I can use a 40V+ opamp and supply it from the input side but that gets old and they guzzle a bit. Simple R-divider step-downs aren't an option on the current design because lots of power is involved and I can't drop a few hundred mV across the shunt this time.

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Regards, Joerg

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Joerg
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Seen Linears LTC6100? To pricy maybe?

petrus bitbyter

Reply to
petrus bitbyter

That's similar to the INA193. LTC mentions just under $2 and I like LTC. However, neither Digikey nor Mouser carries it and that's usually a sign that a part hasn't made it into the mainstream. Kind of a litmus test for me ;-)

--
Regards, Joerg

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Joerg

"Joerg"

Beware of problem below 20mV input voltage. Check the latest datasheet?

AD8211, AD8213 and similar AD parts. Available from digikey, for example.

--
Andrew
Reply to
Andrew

A resistor in series with the - input should add some protection. Or make your own with a r-r opamp and a transistor, 40 cents maybe.

Or make a simple current-mirror-ish sort of thing, or a diffamp, with a couple of BCX71's and a couple of resistors...10 cents and nearly indestructable.

One trick, not super accurate, is to sense the DC voltage drop across the inductor and eliminate the shunt. Then the signal conditioning problem gets much, much worse.

John

Reply to
John Larkin

The LM3485 senses the drop across the mosfet (when on!).

Even less accurate :)

--

John Devereux
Reply to
John Devereux

Or you could sense the free wheeling diode for even worse performance :-)

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Thanks,
Fred.
Reply to
Fred Bartoli

This is getting worse and worse. You guys are great.

Flying capacitor, driven by the switch frequency?

IR temperature sensor aiming at the inductor?

John

Reply to
John Larkin

Wa-a-a-ay back in the late '70's, current transformer, secondary side had a cycle-by-cycle DC restorer, no *WHADDABANG* failures, EVER ;-)

I used it in all the off-line switchers for GenRad Portable Products Division (nee Omnicomp) power supplies.

...Jim Thompson

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| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
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 Stormy on the East Coast today... due to Bush\'s failed policies.
Reply to
Jim Thompson

  1. Smoke detector, aimed at the load?
  2. Microphone, " .
  3. Light meter, " .

Cheers, James Arthur

Reply to
James Arthur

One technique that gets used a lot in signal processing:

Multiply by zero and add what you think it should be.

Cheers

Phil Hobbs

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Reply to
Phil Hobbs

Why not roll your own from a dual PNP? Digikey has several jellybeans:

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(12 cents)

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(4.3 cents)

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(4.1 cents)

Getting fancier, these are matched:

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(15 cents)

And slightly specialized, a bona fide mirror:

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(8.7 cents)

Cheers, James Arthur

Reply to
James Arthur

Shunt + SSR chopper feeding a cheap ISDN transformer, with a bit of step-up for free. Somebody makes a VME thermocouple input module that works sort of like that.

You could counter-wind the inductor: add a second skinny winding that subtracts the AC component and feeds you clean DC, namely the voltage drop across the main current-carrying winding.

Digitize the AC voltage across the inductor and do a DSP thing to detect current based on saturation curves.

Measure the buck duty cycle and the input and load voltages and estimate current.

That last one is not totally insane.

John

Reply to
John Larkin

Or the more general case: Skinner's Constant (aka Flannagan's Finagling Factor)...

"That quantity which, when multiplied by, divided by, added to, or subtracted from the answer you get, gives you the answer you should have gotten." --"Murphy's Law," Bloch

Grins, James Arthur

Reply to
James Arthur

let Sloman design it, and it won't work at all.

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You can\'t have a sense of humor, if you have no sense!
Reply to
Michael A. Terrell

Try Linear's direct ordering.

Reply to
qrk

Sloman has little to say about electronics, and then nothing original or helpful. Ditto "Cranium." They are here to deliver insults, so prefer subjects they can't be called on.

What a choice in life.

John

Reply to
John Larkin

Several of the Linear parts do measure the current into the inductor.

On some of the "roll your own" designs I have done, the current out of the inductor was measured. Basically it was the LM339. On section sensed the current going above the desired and yanked the charge out of a capacitor. Once the current fell below that value, the capacitor would charge back up and the power section switched back on when the voltage hit some magic value.

It took quite a while for the comparator chain and the power device to switch so the current always went above the set point a little.

Reply to
MooseFET

I am sure that'll work but for client circuits I really prefer something that the mainstream distributors carry. If they don't then it might be or become a boutique part.

--
Regards, Joerg

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Reply to
Joerg

They really run up an error budget there but I couldn't see any nasties such as wild glitches. Or is there other stuff?

I am not planning to go that low, mostly I want to current-limit a buck when the sense resistor reaches 50mV or so, in order not to have to dissipate as much as a discrete transistor solution does.

The 8213 is too pricey but the 8211 looks very interesting, around a buck, thanks. It wants +5V supply but I can make one.

--
Regards, Joerg

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Joerg

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