I have a circuit with INA 219. I used the INA219EVM to create my schematic. Rshunt=0.01, R1=R2=10, C1=100n, default config register value. I have no load current.
If i read the bus voltage register I get correct results, but reading the shunt voltage reg I get strange values.
With 0V bus voltage -> shunt 'voltage' (with the values above directly represents current in mA) 0mA (result: OK)
With 5V bus voltage -> shunt 'voltage ~15mA (it should be 0mA with no load)
With 10V bus voltage -> shunt 'voltage' ~30mA (it should be 0mA with no load)
Because I was not satisfied the results, I shorted R1 and R2 and then i got good results (0mA). (Before that I checked R1 and R2: both have 10.4 ohm resistance, so they are mached)
Reading the INA219 datasheet I found that INA219 has NOT the same input inpedance:
Vin+= 20uA; Vin- =20uA || 320k. This additional 320k generates current which current generates voltage on R2(10) which voltage generates differential voltage on INA219 input. At 5V bus voltage this voltage diff is ~156uV that represents 15.6mA current. At 10V@312.5uV@31.25mA. Naturally with R1=R2=0 this diff voltage is 0.
Is my succession correct? If i dont want to remove the input filter resistors(filtering+ESD functions) how can I eliminate this problem? I will try to add 320k parallel with R1 too.
Thanks in advance.
Laszlo.