Maker Pro
Maker Pro

Max038 Help

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!
 
R

Rene Tschaggelar

Jan 1, 1970
0
Motty said:
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?
[snip ]

There is supposed to be a cap from the reference_out to GND.
You have that ?
And it doesn't supply more than 4mA.

Rene
 
T

Tim Shoppa

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?

It's a buffered bandgap reference, so it really should be much closer
to the 2.5V.

Are you grounding all the ground pins? 6,2,9,11,15, and 18 all have to be
at ground, and preferably at a low-impedance ground (something not
necessarily easy on a breadboard). Check pin 17 to be
sure you're really giving it +5V too.

Tim.
 
M

Motty

Jan 1, 1970
0
Rene Tschaggelar said:
Motty said:
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?
[snip ]

There is supposed to be a cap from the reference_out to GND.
You have that ?
And it doesn't supply more than 4mA.

Rene

Well, it basically boils down to me being an idiot. Most things do.
I ran out of space on my protoboard and used a wierd place for another
ground connection and forgot to tie a couple things to it. Great.
Now I am getting around 2.475 - 2.499 volts. The low side is still
lower than the data sheet says the minimum should be. I hope I
haven't messed up the internals by leaving something floating...still
getting a good sine wave out though. Thanks for the reply.
 
S

SioL

Jan 1, 1970
0
Motty said:
Well, it basically boils down to me being an idiot. Most things do.
I ran out of space on my protoboard and used a wierd place for another
ground connection and forgot to tie a couple things to it. Great.
Now I am getting around 2.475 - 2.499 volts. The low side is still
lower than the data sheet says the minimum should be. I hope I
haven't messed up the internals by leaving something floating...still
getting a good sine wave out though. Thanks for the reply.

Good practice in troubleshooting your new design is to check the power
and ground pins with an oscilloscope or a voltmeter. Oscilloscope may
show you that you've forgotten to decouple a power line.

If this is a very expensive chip or you only have one, install a socket and
check the pins before you insert it. 5V parts usually don't like 12V.

Helps eliminate the most obvious errors, only than the real troubleshooting begins.

SioL
 

Similar threads

A
Replies
4
Views
2K
Joel Kolstad
J
J
Replies
1
Views
1K
Jasen Betts
J
J
Replies
18
Views
2K
Rich Grise
R
Top