Hi!
I'm doing preparatory "homework" to explore making a very rudimentary milliohmeter in the near future, just wanted to check a doubt I have. I have some TPS73801s so I can power the circuit from a 9V battery deploying one and use another to make a constant current source. I'm going to try replacing a constant shunt resistor and variable current input with a constant current source and the unknown resistors I'd like to measure (it doesn't need to be a super accurate device).
From what I understand about milliohmeters...I have this so far, and I'm thinking that maybe the battery won't be able to power all this anyway, not even for a few seconds every so often, but let's try:
TPS73801 + (LMC555 monostable driving LMC555 astable) + TPS73801 + INA286 + 7106 (+ 7660).
The first 73801 would be connected directly to the battery and power the various ICs, the second 73801 would be directly connected to the battery and its enable pin would be driven by the 555s, and is intended to provide a constant current source. for a set number of seconds.
I want to use the second 73801 to create a (fairly) constant current source of approx. 10mA or worst case 100mA. I read it is better to use a pulsed current signal to lessen thermal error for milliohm measurements, as it will heat the resistor to be measured less.
I have checked the datasheet again, but can find no info. about enable pin rise and fall time or device settling time after power-up/enable, a) I have limited experience so those points are probably beyond my skills anyway, and b) I doubt that either are important issues for this application.
I hope the information is helpful for providing an informed answer, instead of having to second guess what the device is being used for, and almost need a crystal ball to try to answer.
So the question is:
Can you drive the 73801 configured as a constant current source using the enable pin and an LMC555 in astable mode for about 10 seconds (not sure at what frequency yet, but I think I'd like to keep it in the 10kHz region, based on what the datasheet says in the description and figures 18 and 20)?
- Will this be an unsuitable way of using the device and lead to unpredictable output currents?
Many thanks.