Today I bought a MAX038 function generator, but after trying it with 3 different test circuits the IC doesn't seem to work properly.

For example, I tried it with the circuit below -which is one that comes in the datasheet- and the most I get is only a sort of a sine/saw wave of 200mVpp, offset +0.5V, and at a frequency much higher than what it should.

I also noticed that it doesn't work when you supply it exactly ±5V; it would only work from ±5.14V to ±5.35V and any tiny difference in supply voltage will have a huge effect on output amplitude and frequency.

I would appreciate if anyone could advice me on how to test the IC properly to make sure it's not damaged. Thanks.

 

By the way, what's the meaning of the round symbol on the output (pin 19 center-right of the diagram)

 

Not to thread jack
But where did you find that cause thats not a cheap chip????

 

Not to thread jack
But where did you find that cause thats not a cheap chip????

On ebay, from China. Could that be why it doesn't seem to work?

 

Data sheet schematics almost always work so check it carefully. The round thing represents coax cable out to a test probe.
2 supplies - plus and minus 5?

 

Data sheet schematics almost always work so check it carefully. The round thing represents coax cable out to a test probe.
2 supplies - plus and minus 5?

Thanks, I'm about to give it another try; just trying to figure out where I got it wrong the previous times.

Yesterday I measured the supply voltages, and they are fine +5V and -5V; as I said, it only seems to output something like a sine/saw wave from ±5.14V to ±5.35V, and the output varies a lot between those 2 voltages. I also measure the REF output from the IC (pin 1), and it also seems fine (2.5V)... but can't get a good output.

 

I have to say that I don't have much confidence in the seller. But for $10 I couldn't resist giving it a try.

Every other IC that I got from China through ebay worked perfectly well.

 

My mistake; I'm an idiot.

It's working.

 

Care to clue us in on what the mistake was?

Bob

 

Sorry.

I don't have a dual power supply. So, when I need positive and negative voltages (e.g for op-amps, etc) I use I small splitter circuit (see attach) I made to achieve this from my single power supply.

Obviously, when you need ±5V, since the total voltage output from the power supply is split in two by this circuit, you need a total of +10V. But since this IC has an absolute maximum limit of ±6V, and I was so careful not to burn it, when I connected it I was looking at the power supply, which stated 5V. I also connected a multimeter to the power supply output, and was also reading the 5.14V and 5.34V mentioned above; thinking that I was supplying it the right voltages. But those voltages are the total before the split; so I was only supplying half of the voltage the IC really needed.

Resuming, just a silly mistake for not having a real dual supply.

 

Ouch the splitter approach of yours is just asking for problems. Why not build your self another power supply. And then combine these two then you need a dual supply.

 

Ouch the splitter approach of yours is just asking for problems. Why not build your self another power supply. And then combine these two then you need a dual supply.

You're absolutely right: it only works when you need the exact same amount of current for both polarities; the greater the difference in current needed between positive and negative supply, the less reliable it becomes.

But since I just use it as a quick fix for testing op-amps, comparators and IC function generators, which usually need the same positive and negative current, it does the trick quite well.

I wouldn't use it for anything else than testing purposes; for example, I'm planning on making for the MAX038 its own dual supply from scratch; as soon as I decide which configuration I'm going to use... suggestions are more than welcome.

 

Hello,

You might want to have a look at the following project to create a virtual ground:
Project: CMV2A virtual ground circuit

Bertus

 

Hello,

You might want to have a look at the following project to create a virtual ground:
Project: CMV2A virtual ground circuit

Bertus

Thanks Bertus,

I was looking for a circuit like that to install permanently inside my power supply and add the possibility of dual output; rather than changing the whole design or building a new one from scratch.

The design I posted was quite convenient because I could build it with common components that I had at home; and didn't need to buy anything else. But as I said, it was no good to install permanently because it doesn't work well when the loads on the positive and the negative are different; though it works pretty well with differential amplifiers and function generator ICs.