I am making a robot with multiple devices mounted on top. I am planning to buy either a 14.8v or 11.1v Li-ion battery which has internal BMS limiting maximum discharge current to 4A. Now I need 9v for my motors which will consume 1A each. Additionally I need a 12v and a 5v output to power Jetson Nano and another device. Ideally I would like all 3 outputs to support current up to 5A and minimum 3A so that if in future I buy a better battery and use Jetson Orin, the same power management circuit works for it. The best option I have found is using 3 step down buck converter modules. But is there a way to combine 3 separate buck converters to reduce the size of the PCB to as small as possible so that it can fit in my robot. A circuit/schematic will be really helpful. Additionally I also want to be able to charge the battery and power the robot with charging adapter when I want. So how do I isolate these two operations?
To reduce unwanted interactions (e.g., motor noise vs. control circuits), it's an advantage to have three separate power supplies.
One might derive a 5 V supply from the 12 V rail with resistors and Zener diode if the 5 V requirement were for quite low current, but more likely, the 12 V needs will be low current and 5 V high current, instead.
There are some fairly small commercial converters, e.g. this at ~US$1.50 each, which handles only 3 A. The motors would likely need far more current when stalled than the fixed draw from other devices, so consider adding a supercapacitor to the existing battery and using a higher-current device for the 9 V motor line, e.g. this 5 A buck converter. [One cannot directly parallel voltage regulators for higher current.]
The devices above were just as examples. Also note that some may have high noise and ripple, requiring additional filtering.