MMi203: Power supply
The MMi203 needs a suitable DC power supply connected to the 2-pin "PWR" connector. The positive terminal of the power supply must connect to the pin labeled "+" and the negative terminal must connect to the pin labeled "0V". Please see the article on common terminology for an explanation of the labeling.
Supply voltage
In general, the MMi203 needs a supply voltage between 12VDC and 24VDC. The voltage is allowed to go to a maximum of 32V. Note that the MMi203 operating temperature ratings depend on the supply voltage.
It's quite OK to use an unregulated power supply. Just remember that the ripple will make the voltage instantaneously less than the average DC value, and the board will respond to the instantaneous value. Remember, too, that an unregulated supply can go quite a bit higher than its nominal value, especially when lightly loaded and if the mains voltage is high.
If you are not using the analog functions, you can operate the board down to 10VDC. That means it can for example work off a 12V lead-acid battery (though in a vehicle it may not function during starting, when the battery can get dragged down to well below 10V).
The thermistor function contains a programmable drive voltage that can go up to 20V. If you are using that function you must use a supply voltage at least 2V more than the thermistor drive voltage you are going to program.
It is quite possible for add-on boards to impose additional constraints on the supply voltage. Please refer to the add-on board documentation.
Supply current
The current drawn by the board will depend on the supply voltage, what the board is doing and on any add-ons. Allowing an 2.5mA for an LCD and 5mA for a SPice board, maximum supply current draw versus supply voltage is:
| Voltage | Max current |
|---|---|
| 10V | 115mA |
| 12V | 125mA |
| 15V | 140mA |
| 18V | 160mA |
| 24V | 200mA |
| 28V | 225mA |
| 32V | 250mA |
These figures are calculated based on everything being on at once, including beeper, all indicator LEDs and a full 5mA load on both analog outputs. The figures do not include any external loads (except analog) such as relays.
Note: Figures at 28V and 32V are given for reference only. We do not recommend operating the board at voltages over 24V for sustained periods of time. The board can be damaged if the power supply voltage goes over 32V, even momentarily.