What is the right way to use TPS3839 for power monitoring - Page 1
Forum section: electronics / beginners

author: sairfan1
author_rank: Frequent Contributor
timestamp: October 11, 2023, 03:59:10 pm
content: I'm planning to use TPS3839 in 3.3v battery operated project. As per attached datasheet it says I will be connecting power supply for IC GND, VCC and it will activate RESET' pin when power is below the required level.Here I do not understand its working, looks like when battery got low it will stuck into a loop, it will send a signal to reset MCU, after reset signal, MCU will again power up and that will cause another reset.What I understand, every reset will reduce the load which will reset the circuit and power up the uC and it will continuously reapting. I have SMD component can't try it before design and assemble a PCB, I need help how it will work in a circuit.

author: Buriedcode
author_rank: Super Contributor
timestamp: October 11, 2023, 06:13:46 pm
content: You can certainly prototype SMD parts in solderless breadboards and/or proto board using SMD adapters. Whilst I haven't seen an adapter for the X2SON package, there are many for the SOT23 - and you can even using stripboard or one-hole-per-pad for that. As far as I am aware - the devices are identical in behaviour, so you can just prototype with the easier SOT23.The datasheet mentions both hysteresis - to prevent stuttering output when its close to threshold, and "ignores fast transients". But I assume you're worried that your application draws enough current to cause the power supply voltage to drop more than the hysteresis of the supervisor chip, and long enough to trip the reset - effectively causing it to "hiccup" - so it resets, powers up, draws more power, causes a reset etc..The datasheet mensions there is 200ms delay between the supply voltage dropping below threshold, and the reset line going low so depending on the power up time of your micro that will at least prevent fast oscillation. Also, most microcontrollers have the facility to determine what caused the reset - whether internal brownout, or external reset pin. So perhaps you should include that in your firmware so it can check whether it was reset by a low battery, and take action - such as measure battery voltage, power back down, warn user, or prevent other peripherals from running.

author: coromonadalix
author_rank: Super Contributor
timestamp: October 11, 2023, 09:13:47 pm
content: i dont understand your battery explanation ... do you have a circuit in mind better than a datasheetthes ic's are commonly called "watchdog" "watchdog timer", their job is normally reset the mcu under certain circumstances like power on, it will delay a bit the mcu by resetting it to be sure the supply section is stabilized and ok to run ...it can act as a voltage comparator, under x volts okay i reset everything like the mcu .... over x volts i only reset the mcu once at power on if the supply line doesn't have or do variationsand yes the hysteresis is a defined behaviour to be sure to do the job and be sure it's time to do it and not being affected by some noise and transients as explainedand for the previous thread, you need a more advanced power monitoring ic, if you want to log on/off conditions and other misshaps ... and this one need to memorize them too and not affected by the main supply interuptions if it happenseven a cheap resistor and a capacitor may act as a reset, the capacitor is like a brief short until it began to charge, with the resistor you create a time constant ...you talk about going into a loop, if that happens your supply line is not rock solid and you have reset problems ... or the mcu drive something who can pulse or consume a lot of current in one go

author: sairfan1
author_rank: Frequent Contributor
timestamp: October 11, 2023, 09:23:09 pm
content: @coromonadalixcan you please advise some examples of power monitoring ICs, I would buy and do some experiments, I need for 3.3v circuit and I want when voltage drops a certain level for example 2.5v it totally shoultdown every thing.

author: coromonadalix
author_rank: Super Contributor
timestamp: October 13, 2023, 10:11:08 am
content: do so google search for theses termsvoltage supervisor ichttps://www.ti.com/power-management/supervisor-reset-ic/overview.htmlwatchdog / power goodyou'll get tons of answers, maybe too much ??

author: sairfan1
author_rank: Frequent Contributor
timestamp: October 16, 2023, 03:56:11 pm
content: Thanks that link was helpfulReason to not google rather ask on the forum was I did not want to choose a random part, rather advantage of asking on the forum is that we can get some guidance like parameters to take care of, or someone may share his experience regarding chellenging we may come across.

author: Peabody
author_rank: Super Contributor
timestamp: October 16, 2023, 04:33:28 pm
content: In many cases putting the processor into reset does not materially affect its current draw. But turning off the power completely could indeed bring the battery voltage back up and cause the system to oscillate if the resulting hysteresis is greater than what's provided for in the chip.But I think you should be able to increase the hysteresis of the TPS3839. If you add a resistor in the VDD line, and a feedback resistor to VDD from the output, then it would trip off at a lower voltage, and trip back on at a higher voltage. If you just want one side of that to work, you could insert a diode in the feedback line.