ADC1175-50: Output voltage are random

Hi Amr,

One of our experts will reach out to you within the next day or so.

Regards, Chase

Hey Amr, 

Could you provide some information on the sample rate and clock format you are using? 

Thanks!

Matt

I am using a clock from function generator (GFG-8017G) square pulse (0 to 5V) 1MHz.

Here is the clock signal on the scope.

These are the voltages that i am measuring now with Multimeter with 2V DC input at the VIN of the ADC.

From LSB to MSB

2.3V

2.56V

2.5V

2.63V

2.57V

1.9V

1.3V

4.87V

Hi Amr, is this something that you are seeing on multiple boards/devices?

yes I tried 3 different boards

Any Updates?

Hey Amr, 

How much current is the ADC consuming? Also could you probe one of the digital outputs with that scope? The output is a CMOS output so it should be either low or high. Maybe its toggling between two states? If it is a DC voltage that is actually between VSS and VDD that means the output bits are not being properly driven. 

Regards, 

Matt

The ADC is consuming 19-20 mApmps. with the clock connected and DC of 1.8V measured on it's inputs.

Here is a photo for one of the digital outputs on the oscilloscope. 

Also here is the layout for the board 

Hey Amr, 

So it appears the ADC is sampling and changing the digital outputs. in a perfect world you would expect the bits to stay stable as you are providing it a DC voltage; however there could be some inherit noise on the input that is causing the bits to toggle as you're seeing. 

You could try tying VIN to VRB or VRT and seeing if the output becomes a bit more stable. (output should go to 0x00 or 0xFF) Any noise on the input is going to cause those output bits to toggle, especially as you get towards mid scale. 

Do you have a way to capture this data with a MCU or FPGA? That would be interesting as you might find the ADC is toggling between just a few different codes that are all right next to each other. (0x3F and 0x40 for example). That would explain this behavior. 

Regards, 

Matt

Hello

I displayed the outputs on a picoscope and the decimal values are near each other so the ADC is working fine 

I have 1 more question , I want to add LEDs on the outputs of the ADC , What is the current limit for the maximum sourced current ?

Hey Amr, 

As Chase said you're going to want to use a MOSFET to pull down through an LED. These output drivers are not designed to drive large resistive loads. 

Regards, 

Matt