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ADXRS150 ref voltage fluctuations

Hi guys, m using ADXRS150 solid state gyro for position measurement of a rotating platform (where use fo resolver or pots is not possible i.e. nothing shud be there between static n moving part). the gyro o/p is

2.5vdc in static mode n it varies around 2.5v depending on the rate n direction, hence i'm subtracting the 2.5v (onboard ref from gyro) from the rate out using opamp to get direct rate value which wil giv 0v o/p when platform is static. the problem is, this ref 2.5v keeps varying with slight variations in supply (4.5 to 5.5v). m using bypass cap too! hence, my microcontroller position o/p is dependent on supply too! any suggestions to make it supply variation independent?
Reply to
CCD
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The gyro uses the same reference, so variations should be transparent. Why is the supply rail changing so dramatically? How are you measuring the variations? What does your summing circuit actually look like?

RL

Reply to
legg

The Ref supply rejection is stated at 1mV/V which is 60dB and that's only a typical value. No max is given.

--
Regards, Joerg

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Reply to
Joerg

I built a fairly sensitive device with one of those and that 2.5v ref gave me fits. It's very high impedance and almost everything I connected to that pin (including a plain old ceramic cap) was worse than nothing. In later gyros they got rid of the REF output in favor of other output formats.

--
Ben Jackson AD7GD

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Reply to
Ben Jackson

i measured the variation using oscilloscope (Textronics TDS2024). The summing (or difference) ckt is built with opamp OP27AZ.with 4.7k resistors at both the input terminals and 47k in the feedback (required gain was 10). the rate out of gyro is connected to +ve i/p and the ref 2.5v is connected at -ve i/p

-CCD

Reply to
CCD

I'd load the 2.5V reference pin with ~ 50uA to ground (47k), and bypass it locally.

I'd increase R1 to a minimum of 100K (adjusting other diff gain elements to suit).

This ensures that the reference always sees a load to ground, in spite of biasing requirements of the ICs and gain network, and is never overloaded.

I'd also stick a resistor in series with the comparator's inputs, because I just don't like bare analog IC input pins.

RL

Reply to
legg

Hi, thanx for the suggestions, i'm operating on the limits of the current from ref. I think the biasing suggested by Legg will sort out the problem, I'll check out wiht my ckt. Thankx guys.

Reply to
CCD

Ok, but check the sink capability of that node. It might not have any.

--
Regards, Joerg

http://www.analogconsultants.com/

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Reply to
Joerg

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