I am looking at MAX883 voltage regulator and from the documentation is not very clear whats the difference.

It says this about pin OFF:

In this mode, the pass transistor, control circuit, reference, and all biases are turned off

And this is writen about STBY:

feature that disconnectsthe input from the output when STBY is brought low, but keeps all other circuitry awake. In this mode, V_OUT drops to 0, and the internal biasing circuitry (including the low-battery comparator) remains on.

I understand that there are different elements of the regulator shut down, but I don't understand if the OFF would actualy turn "too much things off" in my usecase:

Using battery (4xAAA for testing for now) for power supply for membrane which is strictly operating on 3V +-0.1V. Therefore I need to hold the voltage at about 3V and when the egulator starts to drop under 2.9V it needs to be shut down to prevent any damage.

  • \$\begingroup\$ What is the membrane and why doesn't it get damaged when the supply voltage naturally rises or falls through 3 volts due to power on/off situations? \$\endgroup\$ – Andy aka Jun 19 '19 at 14:59
  • \$\begingroup\$ micro-dehumidifier.com/wp-content/uploads/2015/12/… this is the membrane. I guess it doesn't damage in on/off situations because it's a short time thing, if it would persist outside the range it would decreased the mambranes lifetime. \$\endgroup\$ – TomasB Jun 19 '19 at 15:12

These questions are usually cleared up if there is a block diagram in the datasheet. As you can see, the off/STBY pin connects to shutdown logic that shuts down everything, including the high side pmosfet switch. If the mosfet is shutdown there will be no draining of the battery.

The LBI , Low Battery Indicator is your logic signal created for your threshold to enable ON, hysteresis, OFF thresholds to make a decision when to go to sleep and when to wake up (like a low battery LED but that drains current).

If you want to use the LBI pin to monitor voltage, then the shutdown circuitry needs to be on (which will drain current slowly). If you want everything to be shut off when the batteries get low, then use the off\STBY with the resistor dividers in figure 3 .

enter image description here

  • \$\begingroup\$ Okay LBO is up in STBY mode - but this won't help because it only shuts down the circuit if the voltage is under 1.2V which is way lower then I need (2.9V). So I guess I have to somehow work with the STBY or OFF pins. \$\endgroup\$ – TomasB Jun 19 '19 at 15:39
  • \$\begingroup\$ Use resistor dividers to get the 1.2 from 2.9 as shown in figure 3 \$\endgroup\$ – Voltage Spike Jun 19 '19 at 15:40
  • \$\begingroup\$ So everything the same as fig. 6 with exception of the divider put in LBI pin instead of STBY. Is that right? \$\endgroup\$ – TomasB Jun 19 '19 at 15:56
  • \$\begingroup\$ TO THE EDITED ANSWER: The fig. 3 measures input voltage - therefore when I get to 2.9V on the OFF pin (of course there would be different value because of the dividers) there would already be 2.9V minus the drop-off voltage on the Vout damaging the membrane. Wouldn't it? \$\endgroup\$ – TomasB Jun 19 '19 at 21:01
  • \$\begingroup\$ Damaging what membrane? \$\endgroup\$ – Voltage Spike Jun 19 '19 at 21:02

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