I bought this Chinese LX-2BUPS which seems very popular:
https://www.aliexpress.com/item/1005005195434497.htmlSee PCB picture below. Here is details:
U1 =
TP4056 - 1A Li-lon Battery Charger
U2,U3 =
XB7608 - One Cell Lithium-ion/Polymer Battery Protection
U4 =
XR2981 - 24W Output Step-up DC/DC Converter
The instance that I got has 4.95V on the output with no load and 4.92 with 1A load, but it seems that its easy to fix to get 5.1V by replacing R7 with formula from datasheet:
R7 = (5.1/1.24-1)*10k = 31 kΩ
In my instance R7=30 kΩ which should produce 4.96V, which well corresponds with measured 4.95V (with take into account resistor tolerance).
It appears that this UPS produce a lot of EMI noise at VHF band (near 145 MHz). Any idea how to reduce it?
At first look, it don't satisfy
XR2981 PCB guide, which require to minimize path from IC to inductor and capacitors. Also it has too large surface for inductor pads which increase parasitic capacitance.
At a glance I think about cut-off excess conductors surface for the inductor and add ferrite beads on the output. What is your thoughts?
Also I notice a huge noise appears when I connect external power, so it seems that
TP4056 layout also has some EMI issue, but I'm not sure what is wrong?