Output pin of Fujitsu MB501 prescaler shows 3.7v regardless of input (2.4/8=300MHz)..

[Terminator3]

Hello! I am trying to debug prescaler circuit. First problem is that i only have 2MHz signal generator and 40MHz oscilloscope to do all things.
Test setup:

NRF24 providing test signal of 2.4GHz divided by first prescaler by 8 (result is = 300MHz).
Then 300MHz comes to the input pin of MB501L (through capacitor provided in data
Regardless input MB501 output pin is always about 3.7v (IC powered by 5v source).
Oscilloscope connected to output pin through capacitor.

Because i can't check if input signal is 300MHz, i tried 2MHz input with different amplitude levels (from MB501's datasheet minimum data provided for 10MHz, i have only 2MHz). But still get only 3.7v. No any AC after capacitor, so i checked pin directly.

So need any idea about how to find the problem

 

[betwixt]

Firstly, check what division ratio you are using. The MB501L can divide by 64, 65, 128 or 129 depending on the voltage at the SW and MC pins.

The manufacturer only specifies it's performance down to 10MHz but I suspect it would work lower as long as your signal generator has a fairly fast rise and fall time. Keep the input level at around 200mV for best results.

Assuming the device is working, you might be seeing instability due to slow rising and falling edges on your signal generator waveform. To check properly you need far better test equipment I'm afraid. Try temprarily linking pins 1 and 8 to ground, both at the same time and see if the output changes. It won't be a conclusive test because you can't predict what state the output flip-flop will stop at but if the 3.7V changes at all it will give an indication that some signal was passing through it and therefore the chances it is working are good.

Brian.

 

[aProgrammer]

MB501L output require a pull down resistor, typically 2.2k, look application circuit into datasheet.

 

[Terminator3]

Thank for your replies, i put 2k transistor directly on that pin, but no luck.
I will try to make simple board with one prescaler later and get some signal generator above 10MHz to find the problem.

 

[Terminator3]

I measured MB501L's input using frequency counter, and it is 300Mhz. So problem with my schematic design or less probably with IC itself.
I fixed all errors in schematic, added pull-down resistor and capacitor on IN2 pin (all values taken from datasheet https://www.qsl.net/n9zia/mc145158/mb501.pdf)
SW and MC pins both connected to ground, so i expect 1/129 division ratio and want to see 300/129=2.3 [MHz], but still no AC...

 

[betwixt]

That matches my data sheet so if the build is correct I'm afraid it leaves only one possibility - a fried MB501L :sad:

Where in the World are you? They can be tricky to find, I think I have some in my stock here but they must be around 20 years old.

Brian.

 

[Terminator3]

I changed IC to the new one and it worked! And also found one error in my PCB: SW pin was connected to ground (must be open or 5v), maybe chip burned somehow. Although total division ratio is not multiple of 10, i am happy with this thing and calculator to measure something higher than 1GHz. Next time i am going to buy other IC, something like MC12080 or MC12054A, also i downloaded list of prescaler IC's somewhere. Maybe you know some good prescalers up to 1GHz?
Thank you all for the answers =)

 

[betwixt]

Well done!

I have a large stock of MC12034 which I use when needed, they are good to 2GHz but I sometimes use MB501L for lower frequencies.

Brian.