ST Micro MEMS Gyro Voltage Reference

Hi all,

I'm looking at using one of ST's MEMS gyros, however - unlike most of their parts, the datasheet is quite sparse on info. Here's the datasheet http://www.st.com/st-web-ui/static/active/en/resource/technical/document/datasheet/CD00254111.pdf

The part is an LY330ALH, which is an analog gyroscope. However, there is a pin on the device VREF, with very little information about it. Page 11 shows an outward arrow from the pin, so I presume it's a voltage reference used for ADCs, but nowhere does it mention what value it is.

In the documentation for an eval board, (one which I cannot find again) the VREF was connected to an MCU pin.

If I do not use the reference, can I safely presume I can leave it floating?

Figure 3 indicates the VRef is an output. I guess this is an internally generated voltage reference for the analogue output voltages. You would route this to the Arduino AREF and select this external reference for your A2D measurements.

My thoughts exactly, but no way of knowing from the datasheet... Strange for newish ST devices...

The zero rate output sits at 0.5Vcc and swings either side to the rails, so surely the Vref is just the max output voltage.

gardner: Figure 3 indicates the VRef is an output. I guess this is an internally generated voltage reference for the analogue output voltages. You would route this to the Arduino AREF and select this external reference for your A2D measurements.

No you wouldn't - the Vref is probably Vdd/2, and putting that on AREF would fail miserably. All analog MEMS accels/gyros I've see use Vdd/2 as the zero level and the signal varies above and below this - Vdd of the sensor is the voltage to use as AREF. I think most are also ratiometric so you don't have to compensate for the supply voltage even.

Its also possible that Vref is simply an internal bandgap reference of about 1.2V, since the application circuit on the datasheet doesn't show it connected it probably fine to ignore it, but you could test to see if it is Vdd/2 reference as that might be handy to pass to another analog input for differential measurement.

All analog MEMS accels/gyros I’ve see use Vdd/2 as the zero level and the
signal varies above and below this - Vdd of the sensor is the voltage to use as AREF.
I think most are also ratiometric so you don’t have to compensate for the supply
voltage even.

This is how I’ve implemented the device, and simply left vref disconnected. I may modify the board to have the vref on a test pad with the mask exposed just to measure it out of interest.