ICL7660(s) LT1044 etc ... voltage converters

[poiureza]

Hello,

I'm looking for a voltage converter with low idle current (pedal is battery operated).
In datasheets they mention "quiescent" current which I suppose is what I'm after.

ICL7760 writes 160-200µA depending on the datasheet 
LCT1044 says 60µA (or 20µA when boost pin is connected.  Funny how boosting the frequency would lower the idle current ...)

Anyway, I tested a handful ICL7660S and LCT1044's in their negative voltage config and with a 9V battery. Boost pin connected to V+
Without any load I measure 1.8mA idle current drawn from the battery for the ICL's and a whopping 15mA for the LCT's

Where am I wrong ?

[antonis]

LTC7660 is equivalent to LTC1044..
https://www.analog.com/media/en/technical-documentation/data-sheets/ltc1044_7660.pdf

(The only LCT1044 I'm aware of is an Amstrad LCD portable TV set.. )

Datasheet declare 200μA (max) NO LOAD supply current at +5V..
(should we presume your DMM's impedance isn't infinite..??)

[MikeA]

+1 to antonis on the LTC1044 specs, they're +2 or +5V, no load.  +9V is allowed (barely) but not defined.

Pin 1 on the Maxim ICL7660 is not a boost, it's undefined, so that may be an issue.

[Clint Eastwood]

The datasheet from Maxim (https://datasheets.maximintegrated.com/en/ds/ICL7660-MAX1044.pdf) has a graph showing quiescent current vs supply voltage. At 9 volts it gets rather high indeed.
Maybe the ltc1044a would have lower idle current at 9 volts, it has a higher supply max of 13 volts.

[Rob Strand]

The datasheet from Maxim

It pays to scrape through the datasheets and app notes from the different manufacturers on these things.   Some throw in extra nuggets of info which are very useful,  especially in the plots.

[poiureza]

Thank you everyone

Yes LTC1044, not LCT1044 sorry
I mesure in series with my battery, not on the load side, so DMM impedance is irrelevant I think
My ICL7760 are actually ICL7660scpaz, so they do have a boost pin

Many thanks for the Maxim data sheet, I checked a lot but not that one.
@20-25kHz I read about 200µA, still not the values I measure.

Anyway, mystery solved :
Values of 1.8mA and 15mA go down to ~200-300µA when I remove the boost pins and keep the conversion freq in the audio band
Thus voltage converters go in the parts bin and I'm back to our usual Vref@4.5Volts ...

Bummer

[Clint Eastwood]

I don't know what negative voltage you need, but You can make your own converter using a good old 555 timer, the cmos versions like tlc555 will use very little current. Here is an example, 9 to -8.4 volt, about 40khz, idle current about 300 uA.





But this only works well if you don't need more than about 10 mA.

[antonis]

I mesure in series with my battery, not on the load side, so DMM impedance is irrelevant I think

Can't figure out how this can be implement, but let it be..

[Processaurus]

The two chips have a max voltage that is too low to be reliable long term. The regular 7660 is 10.5v absolute max and LTC1044 is 9.5v absolute max. I've had them burn out. 

The 1044 and 7660 were designed for +5v, to make a +/-5v supply for analog stuff in digital circuits.

The 7660A is rated for 13v max, better, but doesn't have the 35kHz boost to the oscillator, it's stuck at 10kHz so it may whine depending on the layout. Bummer. Any newer DC-DC converters with better specs?

[Processaurus]

Oh yeah, forgot about the LT1054, WAY better for stompbox use at 9v. Max input voltage 15v, oscillator frequency is 25kHz:

https://www.mouser.com/ProductDetail/Texas-Instruments/LT1054IP?qs=paYhMW8qfitwFCC4i5I0HQ%3D%3D

[poiureza]

Oh ! TLC555 might do the trick, I'm fine with 10mA max current.
I wasn't aware of a CMOS version.  The NE555 draws 5mA idle current, so I didn't look further ...
8 passive components though
No stock @mouser.be (procurement time = 73 weeks  )
Back to bummer ...

LT1054 supply is 3mA, no go here
The 7660S works up to 12V :
https://www.renesas.com/us/en/document/dst/icl7660s-icl7660a-datasheet

[Clint Eastwood]

TLC555 is from Texas Instruments,  but others also make cmos 555's. I was curious, and saw that mouser.be has the ICM7555 from Renesas. 20.000 in stock. But Mouser has a quite high delivery fee. Farnell or TME europe are a better deal I think.
Yes, you have a few  more components, but you can choose the oscilator frequency yourself.

Good luck!

[ronh]

Hi Clint.  The convertor you posted brought back memories.  Back in the mid 90s I was designing and building my own overdrive pedal.  I wanted the op-amp to be biased with a bi-polar supply.  So I built the one you posted and tested the circuit out.  It sounded great until the 555 chip went up in smoke.     Under max load I got -3Vdc @ 10 mill.  Fun times.

[Clint Eastwood]

Hi ronh,

That seems like very poor performance from the circuit. Wonder what went wrong there. Here is a paper from TI discussing the use of the TLC555 as charge pump, it includes graphs showing output voltage vs load current: https://www.ti.com/lit/an/slfa002/slfa002.pdf?ts=1651647297321&ref_url=https%253A%252F%252Fwww.google.com%252F
10 mA should not be a problem. But to be honest, I have only used this circuit with a few mA load max.

[antonis]

Everytime someone doubts about pushing a device to its current limits, a series pass transistor smirks..

[anotherjim]

When charge pump output current limits are reached, the buck-boost converter takes over.
https://electronics-project-hub.com/boost-converter-circuit-using-ic-555/