MyPi Power Input Range

One of the questions that comes up a lot is "Can we run the MyPi board with a 24V PSU?"

The short answer to this is "Yes you can", to answer this question fully we need to fill in a bit of detail on why the top input range was originally specified as 23V not 24V.

The power converter chips used on the MyPi board are AP6503 buck converters from Diodes Inc - see AP6503 Data-sheet - these parts have a wide input range with absolute maximum input of 26V

So far, so good.

The data-sheet also gives a maximum recommended ratings of the chip, specifying the input voltage range of 4.7V to 23V along with an ambient operational temperature range of -40°C to +85 °C. These parameters together form the operational envelope in which the device must always be able to meet it's guaranteed 3A current output when given a range of input/output voltages (see datasheet page 9 for more info) . The datasheet then states that "The device function is not guaranteed outside of the recommended operating conditions".

As our application is working well within the operational envelope for the most part (in terms of input/output voltage differential, current demands and operational temperature range) to get further clarification on this we've had discussions regarding the datasheet input voltage range maximum vs recommended values with our local Diodes Inc Field Application Engineer. The FAE confirmed our thinking in that whilst the devices are tested to guarantee operation in the recommended ranges section 24V operation should not be a problem provided care is taken not to exceed the datasheet absolute maximum ratings.

As a result we performed our own internal testing running multiple units for extended periods at 25V input (Giving 24.7V measured at the AP6503 input) under different system loads without problem.

To protect the power supply section from both incorrect wiring and transient input voltage spikes the board is fitted with both a reversed input polarity protection diode and a Transguard device at the main power input, this will however not prevent a full over-voltage sitation so care should be taken that the input voltage does not exceed 26V as the buck converters will be damaged if >=27V is applied.

To summerise, whilst we cannot guarantee full parametric operation at 24V over the entire operational temperature range of the device (in line with the Diodes Inc datasheet) on the face of it there doesn't appear to be a problem with running the board at 24V.

We would of course advise customers to carry out their own testing to ensure compatibility for their application.