Problems setting up gyroscope

[chris414]

Hi everyone. I've got a gyroscope that I'm using for a balancing robot, however am not so sure about the connections. I've bought the evaluation board of the ADXRS613 gyroscope.

ADXRS613 datasheet: https://www.electro-tech-online.com/custompdfs/2010/01/ADXRS613.pdf
ADXRS613 eval board datasheet: https://www.electro-tech-online.com/custompdfs/2010/01/EVAL-ADXRS613.pdf

At this point I just need to get it up and running, I'm not too concerned with setting the bandwidth (supposedly the eval board has done it already) and doing self tests etc. A few things I'm not sure about:

- What is the difference between the analogue supply voltage and charge pump supply voltage? The evaluation board datasheet says it has left them disconnected, but I can't see any reason in my application why i'd want to bring in a new voltage to the system... can I just connect them both to the same 5V and their earths to the same earth?
- Can I leave the pins which are not being used for power supply as floating, eg. the self test pins? If not, what should I do with them? Can I just put a 1K resistor between the pin and ground?
- What does the SUMJ pin do and do I need it / does it need to be tied to ground?

Thanks for the help!

 

[chris414]

anyone, please?

 

[Blueteeth]

- What is the difference between the analogue supply voltage and charge pump supply voltage? The evaluation board datasheet says it has left them disconnected, but I can't see any reason in my application why i'd want to bring in a new voltage to the system... can I just connect them both to the same 5V and their earths to the same earth?

Datasheet circuit description (from the eval board datasheet):
The analog and power grounds (AGND and PGND) have separate power planes in this evaluation board to accommodate application-specific grounding schemes. If the user requires only a single ground plane, these nodes can be shorted together. Both AGND and PGND must be grounded for the evaluation board to operate properly. Note that the analog supply voltage and charge pump supply voltage (AVCC and VDD) are not connected on the EVAL-ADXRS613 and that users may connect these as appropriate to their application.

So, the answeris 'yes', you can connect both the Vdd and AVcc together, as they are both 5v. And connect the analogue and digital grounds together. They seperate the two power supplies because it is up to the user/designer to determine how and if they split the ground planes. Thepower pins aren't conected together because they want to give the user the option of using two isolated power supplies for countering noise problems. These are both +5V.

- Can I leave the pins which are not being used for power supply as floating, eg. the self test pins? If not, what should I do with them? Can I just put a 1K resistor between the pin and ground?

Quote from chips datasheet:
ST1 and ST2 are activated by applying a voltage of greater than
0.8 × VRATIO to the ST1 and ST2 pins. ST1 and ST2 are deacti-
vated by applying a voltage of less than 0.2 × VRATIO to the ST1 and ST2 pins. The voltage applied to ST1 and ST2 must never be greater than AVCC.

- What does the SUMJ pin do and do I need it / does it need to be tied to ground?

Again, look at the chips datasheet, first page. It has that pin with a 100nF capacitor to the 'RATEOUT' pin. I believe the evaluation board has this capacitor already installed to give a fixed update rate. You can of course add your own resistor/capacitor combination between SUMJ and RATEOUT to modify this update rate, as per the chips datasheet, page 9 'setting bandwidth'.


I will admit the evaluation boards datasheet is skimpy, but it doesn't actually have anything on board apart from bypass caps. The chips' datasheet however, contains all the information you need, especially in 'applications information'. Datasheets are there to be useful, a source of information, you just need to look in the right places