High eff. automotive buck SMPS chip?

Please post _existing_ .ASC ...Jim Thompson

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

| 1962 | I love to cook with wine. Sometimes I even put it in the food.

Hi Jim!

There is no .ASC. It's a simple LM22676, nothing special.

I'm looking for either another part, or a cute way to bodge in a sync. rectifier to replace the catch diode.

This is an old trick from the Tek 7104 (IIRC) 'scopes: L1 _ _ _ _ ----+---' | ' ' '-----+----> Vout | | | | |/ --- C1 '---| Q1 --- |

There's probably a synchronous switcher chip around somewhere that does what you want.

But consider something like this as a starting point for discussion:

The SimpleSwitchers were pretty slow, so the gate might be persuaded to switch early, reducing shoot-through. If this works, it might add

40 cents to the BOM.

--

John Larkin         Highland Technology, Inc 

jlarkin at highlandtechnology dot com 
http://www.highlandtechnology.com 

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom laser drivers and controllers 
Photonics and fiberoptic TTL data links 
VME thermocouple, LVDT, synchro   acquisition and simulation

Hey, you don't need the resistor!

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators

Probably. I spent some time searching, but the S/N is terrible-- DigiKey has >18,000 SMPS chips.

This one looks like a "maybe":

It's pretty nice, but not as rugged as the Simple Switcher's

43V Vcc(max).

Here's my modernized version of the Tek technique:

======= .-.-.-. L1 .--+----+---' ' ' '----+----+---> Vout | | | | | | ,-' | | | | ^ D1 | | | | | | | --- C1

--. | === | ======= | --- | | | The SimpleSwitchers were pretty slow, so the gate might be persuaded

The LM22676 runs near 500KHz, so it's rather zippy for a SS. The best circuits I've sketched so far sense the inductor current via a tap, such that when you drive L1 the auto-transformer action cuts off the sych. rectifier automatically. Slick, but custom.

The smart thing is probably to use the AOZ1231 and be done with it, but then I've got to add load-dump over-voltage protection--Vcc(max)=28v is not enough. Ick.

Cheers, James

Assuming automotive means several 100k units/year, talk to Linear about their LTC3810. Comes in a 100V edition which is great for automotive. Unfortunately around $4 but that is the price for 100. If they can't come down enough, look for something similar. If you don't feel like sloshing through all the mfgs price lists tell your facvorites distributors "Find me something similar for a buck fifty". The external FETs are cheap. It allows higher frequencies so you save on the inductor.

Then there is this one, but haven't tried it myself:

(but check for stock)

--
Regards, Joerg 

http://www.analogconsultants.com/

That's a beauty Joerg. Stock is a bit scary, but it's a good prospect. Thanks!

Cheers, James

I found these recently - would need some help for automotive load dump (only 28V max) and reverse protection but dead cheap:

Vishay SIC402A £0.68 500 off from Farnell so in real numbers