Why INA293 provide discontinuous reading on low duty PWM signals?

Question

INA293 has 110V common-mode voltage

1MHz gain bandwidth

my signal 90V, 100Hz PWM, 10%-25% duty,

load current 30mA max

shunt resistor 5 Ohm

the gain of ic 20V/V

Vout = 30mA x 20V/V x 5 Ohm = 3V

i use esp32 adc to meaure Vout (Vout propotional to current)

at 100% duty only I get a continuous current reading

at 10% duty, or less than 80% duty current measurement is not continuous, it gives zeros in between.. why is that happening?

my load is not inductive as well, same time load is on only for like 0.5sec,1 sec or 2 sec

I cannot use a low pass filter due to PWM pulses are required for my load

Answer 1

The INA293 has a wide bandwidth and high slew rate relative to your 100 Hz PWM, so it will follow the actual current through the load which is a square wave. To get a continuous measurement representing the average current you need to integrate readings over the PWM period.

You can do this in software after the readings have been converted to digital numeric form. First take readings until you see the value drop to 0 and then go higher. This is the start of the PWM cycle. Then continue taking readings and and adding them to an accumulated total until you see the current drop to 0 again. Since the PWM period is fixed, you now just have to divide the accumulated total by the number of readings that would be made over a whole PWM period. eg. if the ESP32 is sampling at 6000 samples per second then divide the total by 60 (6000 sps / 100 Hz).