M
Motty
- Jan 1, 1970
- 0
I am using a Max038 function generator IC in the configuration
that the data sheet specifies for normal operation. I am just
prototyping right now so I am using a 100k pot tied to Vref and ground
to generate the Iin currents. For some reason my Vref is not at 2.5
volts. It is around 2.1 V. I took the cap out that is tied from Vref
to ground and the voltage went up to about 2.25. I am under the
assumption that Vref should ALWAYS be 2.5V. Is this correct? Again,
I
am prototyping on a proto-board so I know there are probably
undesirable
noise issues, but I've tried to be as careful as possible making
traces
short and keeping rogue capacitance to a minimum.
I also had this problem some time ago when I first started this
project.
I was wire wrapping on a regular breadboard at that time. The same
problem was occuring. The circuit seems to be working corectly
though.
I've tested it through an amplifier and it is defintely producing a
good
sounding sine wave and the frequency is variable, but I can't
accurately
design the Iin current, and thus the frequencies I want, if I don't
know
what the Vref is going to be.
I have three IC's and have tried them all. They all produce the same
results. I have also looked at the evaluation board and how it is
routed. I can't think of why the Vref is not 2.5V. It's an internal
voltage reference so external parts shouldn't have an effect on it
right (unless you exceed the 4mA Vref current rating)? Power is being
supplied by lots of batteries and 7x05 voltage
regulators that can supply the needed current to the chip. I might
not have been as careful bypassing the power supplies of the Max038,
but that shouldn't have a detrimental effect on Vref I wouldn't think.
Please help. This is
going to be a cool guitar effect pedal one day!
that the data sheet specifies for normal operation. I am just
prototyping right now so I am using a 100k pot tied to Vref and ground
to generate the Iin currents. For some reason my Vref is not at 2.5
volts. It is around 2.1 V. I took the cap out that is tied from Vref
to ground and the voltage went up to about 2.25. I am under the
assumption that Vref should ALWAYS be 2.5V. Is this correct? Again,
I
am prototyping on a proto-board so I know there are probably
undesirable
noise issues, but I've tried to be as careful as possible making
traces
short and keeping rogue capacitance to a minimum.
I also had this problem some time ago when I first started this
project.
I was wire wrapping on a regular breadboard at that time. The same
problem was occuring. The circuit seems to be working corectly
though.
I've tested it through an amplifier and it is defintely producing a
good
sounding sine wave and the frequency is variable, but I can't
accurately
design the Iin current, and thus the frequencies I want, if I don't
know
what the Vref is going to be.
I have three IC's and have tried them all. They all produce the same
results. I have also looked at the evaluation board and how it is
routed. I can't think of why the Vref is not 2.5V. It's an internal
voltage reference so external parts shouldn't have an effect on it
right (unless you exceed the 4mA Vref current rating)? Power is being
supplied by lots of batteries and 7x05 voltage
regulators that can supply the needed current to the chip. I might
not have been as careful bypassing the power supplies of the Max038,
but that shouldn't have a detrimental effect on Vref I wouldn't think.
Please help. This is
going to be a cool guitar effect pedal one day!