has anyone used a LTC3532 buck boost regulator

There's no difference between this device and any other voltage mode converter - for fast transient response and to avoid the double pole you need to add extra filtering.

The RHP zero (which would normally be designed such that it provides phase boost during final gain roll-off) is at too high a frequency in boost mode (usually) to act as phase boost for this rather critical frequency region, so a type III filter is used instead to get proper phase response *and* fast transient (loop frequency) response..

If you can live with slower loop response, then use a type I filter as explained in the text.

As far as I can see, the text is perfectly straightforward. In genereal, LTC's datasheets are superior to most for their power converters.

Cheers

PeteS

Thanks Pete The problem I'm having is that my last analog filter experience was 18 years ago at tech. All I really want from this device is a 3.3 V supply from a 3.6v lithium cell to power my microcrontroller and bluetooth. The current profile is 0.5mA (sleep), 30 mA (on), 60mA (on + bluetooth). Since size is not critical I wanted to use the 300kz switching frequency to get maximum efficiency. So the example circuit looks ok but it uses a higher switching frequency. I think the data sheet is very detailed but for all its detail it is very thin on application examples that dont depend on extensive prior experience. It would be greatly improved if there were a complete worked trhough example which detailed all the assumptions made. A good example of this deficiency is in the calculation of the inductance - there are two formulae one for buck and one for boost, but there is no explanation of what to do with the different results, i assume we use the maximum value but its not clear at all to the new user. Also "The inductor ripple current is typically set to 20% to 40%" what are the implications of using 20% as opposed to 40%? So for a someone with primarily digital experience this is a hard part to get to know.

otilija

PeteS wrote:

OK

What you need then is a power supply that has the following characteristics:

1. Stable from no-load to about 500mA (the bluetooth module will slurp current in pulses and the supply has to be able to withstand it).

1. Has to operate in buck-boost mode (although it's not a SEPIC converter).

2. Needs fast transient response (bluetooth again).

Note that although the average current for RF devices is fairly low, the peak currents can be quite high (GSM / GPRS for example can be 2A peak pulses), so transient response is very important in this application.

Give me time to have my dinner and I'll do my good deed [tm] for the week and give you suggested values.

Cheers

PeteS