Other Parts Discussed in Thread: TLV713P, , TPS62125
We are designing a 12V to 3.3V (Buck + LDO) Power Supply for Bluetooth MESH network. We are using TPS62122 to step down 12V to 3.6V and filtering the output ripple through TLV713P to get 3.3V.
In total, 30 Bluetooth Nodes will be connected to a 12V line over 100 meters. Average and Peak Current Consumptions of each Bluetooth Node are 5.5mA and 25mA (9.9mA RX, 25mA TX and 1.4uA Sleep).
We request help on the below,
1) What is the recommended capacitor on TPS62122 input (12V) side considering the long distance from power source? (The TPS62122 datasheet recommends using 4.7uF ceramic. Is another 4.7uF in parallel sufficient considering peak load current 25mA)
2) Is 12V for main line a right choice? Need opinion please.
(Let me explain why we chose 12V over 24V or 48V.
Firstly, calculating for the worst-case scenario of all 30 Bluetooth Nodes consuming peak 25mA and TPS62122 working at 80% efficient, the maximum current drawn from 12V source is ((3.6*0.025*30)/(0.8*12)) = 0.281A
Eventhough current drops at each Bluetooth node and only 0.025A reaches the last node at 100m, to simplify calculations, consider full 0.281A travels 100m over an AWG20 wire, this creates 1.87V drop. So, the worst-case Voltage at the 100m Node is 10.13V which TPS62122 can still convert to 3.6V.
Secondly, cost. 12V Buck Converter costs less and takes-up much less space than 48V)