We have to admit that we are a huge fan of Linear Technology. Their product never fails to impress but the only annoying aspect of their product would be price. When designing power supply section, we tend to have this sequence of vendor preference: LT > TI > NI > Microchip > Exar > etc. Our initial design on the Ultra board was to use 2 parts from LT. These 2 parts are:
Both of these boys were tested on the R1.00 Ultra board and works perfectly fine. Apart from the tricky and careful PCB layout for these 2 parts, LTC3530 requires a total of 12 external components. We think these external components takes quite an amount of space and also affect the accuracy (yes, we are obsessed about accuracy!) of the output voltage due to the tolerance of these external components.
Couple of months back, we came across a flashy TI advertisement for their buck-boost converter TPS63001. This tiny little guy comes in a DFN10 (TI called them SON10) package. Apart from the annoying package, it requires only 3 external components to work, 2 decoupling capacitors and 1 power inductor. The quiescent current is comparable to that of LTC3530 and it provides a higher output current at 3.3 V. It’s lower cost (also considering the less external components and space) compared to the LTC3530. So, we decided to unplugged LTC3530 out from the design and replace it with TPS63001 to simplify things up from design point of view and also cost. We have rearrange some of the more sensitive tracks on the layout after the removal of the LTC3530 and it’s 12 companions.
LTC4090-5 is a complete USB power manager that takes care of Li-Ion/Polymer battery charging process from the external source and also through the USB port. We definitely love the fact that this tiny guy can take in up to 38 V. We thought of using some standard 12 V solar panel to provide necessary charging when the board is used for remote applications. We are sticking with this part for the next revision of Ultra.
We have completed the changes on the R1.00 of Ultra board and would be sending out R1.10 to the PCB manufacturer pretty soon. We are still waiting for 1 SMT connector (ISP 6 pin connector) to arrive from 4UConnector, just to check for mechanical clearance before sending out the boards (we hate endless supplies of coasters!!!). Finger crossed, we hope there ain’t anymore mistake and changes.