G431B-esc1 and current sense

developement
1

i try to use the current sensing with the esc G431B-esc1.

i read a lot here in the community and i see often:

LowsideCurrentSense currentSense = LowsideCurrentSense(0.003, -64.0/7.0, A_OP1_OUT, A_OP2_OUT, A_OP3_OUT);

i understand 0.003 the shunt value 3 mOhm!
64.0 can be the gain of the opamp!

but 7.0 where does this value come from??? this I need!!

i look at the init of the opamp in the source… and compare with data sheet.
i expected a gain of 16 from how you init the opamp:

hopamp->Init.PowerMode = OPAMP_POWERMODE_HIGHSPEED;
hopamp->Init.Mode = OPAMP_PGA_MODE;
hopamp->Init.NonInvertingInput = OPAMP_NONINVERTINGINPUT_IO0;
hopamp->Init.InternalOutput = DISABLE;
hopamp->Init.TimerControlledMuxmode = OPAMP_TIMERCONTROLLEDMUXMODE_DISABLE;
hopamp->Init.PgaConnect = OPAMP_PGA_CONNECT_INVERTINGINPUT_IO0_BIAS;
hopamp->Init.PgaGain = OPAMP_PGA_GAIN_16_OR_MINUS_15; THIS !!!
hopamp->Init.UserTrimming = OPAMP_TRIMMING_FACTORY;

can somebody explain a little?

i am very new to this, but i got the motor spinning in open loop and i can move the motor to a fixed angle. can read the bemf voltages.
but the current readings are wrong. i not use a hardware encoder. i know this is not easy. but i want dig deep into this.
if I use gain of 16 the current vals are very much wrong.
if i use 64/7 = 9.14 the currents is still a little off: i should get 1.1A in my test scene, but adc value gives 0.97A not much diff … but !!!
adc delta is 32 digits. 32digit x gain 9.14 / 0.003 → 97 → 0.97A ?

thanks for helping
Frankers

2

The resolution and accuracy of the current reading on this board just isn’t that good, that’s better than I ever got. It’s not even very linearly correlated with the actual current, especially at the lower ranges. It’s not going to be the same as an ammeter. If you really needed to improve it you’d probably have to make some kind of calibration apparatus and record the actual reading, then make a look up table or polynomial to correct the reported reading, translating it to actual.