Decreased current consumption after change of PCB-supplier.
Decreased current consumption after change of PCB-supplier.
(OP)
Any ideas what can cause a decrease in supply current of ~10mA (from 54 to 45mA @5VDC) after changing supplier for the PCB? The board is of 2 layer FR4, used in a RF unit module of size 10x10cm. All components are from the same batches as before, the only difference is as mentioned a new (chinese) supplier for the PCB, ordered with same specs.





RE: Decreased current consumption after change of PCB-supplier.
RE: Decreased current consumption after change of PCB-supplier.
RE: Decreased current consumption after change of PCB-supplier.
RE: Decreased current consumption after change of PCB-supplier.
To ensure correct impedance, you need to be as specific as possible in specing the board...finalized copper weight, percentage of trace over/undercut after etching, thickness of each laminate layer (particularly the die. constant), thickness of soldermask, etc.
RE: Decreased current consumption after change of PCB-supplier.
I measured the thickness of the two types of PCB and they differ with ~2,5mil. The one with lower I_supply is thinner (33.7mil). So I guess the next step is trying to put a test strip on the PCB for impedance measurements and write a bit stricter specs.
RE: Decreased current consumption after change of PCB-supplier.
20% of change in power consumption deserves a serious look. Don't let these boards go out before you understand what happens, or you may have bad surprises in the field. Aside from the power consumption do you see any difference in performance?
If your board hasn't too many parts on it, you may consider moving parts from one pcb to the other, and record any differences in power consumption.
RE: Decreased current consumption after change of PCB-supplier.
RE: Decreased current consumption after change of PCB-supplier.
You have
1) 54mA x 5V = 270mW
2) 45mA x 5V = 225mW
So you have a "massive" 45mW difference between the two systems. It really depends what is dissipating the power in the system. If most of the power is being dissipated in one chip then that much change of dissipation is quite possible.
There is too little power dissipation for the copper thickness to make any difference at all.
If the whole board is thrashing around at high frequency then the dissipation factor of the pcb might be that different from board to board.
I liked felixc’s idea of swapping parts from one board to the other, depending on how good your re-work skills are.
RE: Decreased current consumption after change of PCB-supplier.
The impedance of the traces alone is likely not the cause (unless we are talking about a sizable board or trace length/width). However, the impedance change may affect any other circuits designed for maximum power transfer, which in turn would affect the current.
RE: Decreased current consumption after change of PCB-supplier.
The board is by the way a direct convertion thing workning @2.45GHz. One thing I forgot to mention is the fact that this new board has a lower P_out than the old one when using the same resistor values (as in the old) in a T-network used for trimming of P_out. But trimming P_out up doesn't affect the current...
This complies with the idea Comcokid had about the RFICs.
I will try the part swapping after I have finished all the %€#¤!! paperwork on my desk.
RE: Decreased current consumption after change of PCB-supplier.
More data gives a more accurate/probable theory