Following my question Powering up analog part of the video card (thanks everyone for their inputs and advices) I have chosen the devices, and even have drawn the circuit diagram of 12 V to 5 V power converter:
Output current is expected to be approx 250 mA, maximum 500 mA.
I was very happy, until I found the following article, which made me very upset. It is in Russian, but I translate key points.
The TPS562200 is having some serious drawbacks:
- Causing it to physically burn if layout is not followed - in particular there must be no switching current under the chip. Good to know before routing the board.
- Vias are required as VBST and SW pins are put at the different sides of the chip. Also good to know.
- Very high ripple under low load.
The last one seems actually being killing the whole design. According to calculations, the current when device goes into Advanced Eco-Mode Control mode (datasheet, chapter 7.3.2, page 12) if load consumes less than 500 mA => in my device the regulator will always be in this mode.
Article considers this case with very demonstrative pictures:
This noise would be a huge issue for the analog circuits. I see two ways to deal with it:
- change regulator with one rated for smaller current - for example, TPS560200, then "The transition point to the light load operation" will happen at 230 mA. However I suspect most of the times less current will be consumed from the supply, and it may easily happen that switcher will work in this featured ecomode.
- Keep this ADP3339 High Accuracy, Ultralow IQ, 1.5 A, anyCAP Low Dropout Regulator. It has very nice ripple rejection property:
and this ripple under 100 kHz is expected to be attenuated greatly.
Is this ripple effect will take place under "lighter" loads for any switcher, or it is a "feature" of these TPS ones?
Do you think the design is acceptable for powering analog video circuits - would selected LDO cure the issue created by the TPS?
Maybe you can propose something better than I have drafted?
following Marcus's advice I tried Webench (previously I was using it in relation to TPS562200 only). I set requirements of 12 Vin, 6 Vout, max current 0.5A, and nominal current of 0.2A... and have got 53 results, one of them is this TPS562200!
I forgot one of the requirements I have: chips must be solderable by hand by not-so-experienced individual. Thus most appropriate packages are SO or SOT.