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efficient buck-boost at 60mW (3V, 20mA)

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bnevins

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I am looking for a chip or module which can convert a battery voltage to 3.0V out (possibly 5V out) at about 20mA.
Efficiency is very important.
Vin may be greater or less than Vout, so buck-boost, SEPIC, others?

Currently using LTC3531.

I wonder if there is a more efficient part for this current range.
Alternatives I have found: TPS63020, LT3464
 

The LTC3531 is going to be pretty difficult to beat with such low output voltages, since it uses fully synchronous rectification. Using a micropower boost like the LT3464 seems reasonable but the diode in the SEPIC would eat a large chunk of your efficiency.

What it your Vin range? Would the LTC3335 work?
 

Micrel and microchip have some cheap offerings for this.
Remember also you can use low voltage schottky with very low vf.
You can even ride "bare-back" and do a roll-your-own microcontroller controlled boost with no source sense resistor...as that will eat up a decent proportion of your power. Just do on/off control. A comparator based feedback. Do a soft start with duty cycle gradually increasing.
 

The Vin is 3.0V now, but the battery chemistry has not been chosen.

Some kind of hysteretic control, using 1-2 comparators might be a good choice.
 

Then why not use a micropower boost IC? Making a discrete controller with comparable efficiency is probably not doable.
 

You say efficiency is very important but without some
quantification of this (%) and target cost it would be
pretty difficult to make a value judgment about stuff
like topology. You can probably throw solution size in
there too. Along with whether you require fixed
frequency or can stand a hysteretic style.
 

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