DAC5688: Wave glitch on CHA or CHB

Hi Juan,

I am waiting for the evaluation module for this device to show up at our lab. Once I receive this (5-7 days), I will run your configuration on our hardware and let you know of the results. In the meantime, could you upload an image of this "glitch" so I can better understand what exactly you are seeing? Also, is this something you are seeing on a single device or is this across numerous devices? Welcome to E2E.

Thanks, Chase

Thank you for your anwser Chase.

To detect the glitch with more visibility we are using ramp signals, frequency = 500 KHz. The amplitude doesnt matter because the glitches always appear in the same places. You said "Also, is this something you are seeing on a single device or is this across numerous devices" To answer your question, we are testing on 3 different boards (devices) with the same hardware and each of one give us the same result

This is the DAC outputs with CONFIG1 = 0x0D. (DA = green ; DB = yellow)

This is the DAC DB output with CONFIG1 = 0x09, the glitch is more visible.

To add more information about the clocks, the CLK2 has a LVDS 3.3V format and the CLK1 has LVCMOS 3.3V

I had made a mistake with the following registers, these are the actual values

Hi Chase,

Do you have any update for me ?

Regards,

Juan Camilo Peña A.

Hi Juan,

Sincerest apologies for the delay. We have received an EVM and I have it set up with the configuration you have described. I will start testing first thing on Monday and get back to you with the results.

Best,

Luke Allen

Hello Juan,

I have taken some measurements using the DAC5688 EVM with the clocking setup you have described above.

• Clk1 - Single Ended, 250MHz
• Clk2 - Differential, 500MHz 

I generated a 1MHz sine wave and sent it to the DAC using HSDC Pro and I am not seeing any glitching like you have described. Shown below is the outputs I measured, output channel A is shown in yellow and output channel B is shown in orange. Additionally, changing this inv_inclk bit has no effect on the output signals.

It could be possible that for your application, some other aspect of the design is affecting the output. Below I have included the register config file that I used for your reference.

Texas Instruments Inc.
DAC5688 EVM Register Configuration

DAC5688 Registers
Address	Data
00		01
01		09
02		20
03		00
04		19
05		10
06		00
07		00
08		00
09		00
0A		00
0B		20
0C		A6
0D		A6
0E		00
0F		2D
10		00
11		00
12		00
13		00
14		00
15		00
16		AA
17		10
18		80
19		00
1A		0E
1B		FF
1C		00
1D		00
1E		00

CDCM7005 Registers
Address	Data
00		005FF1F0
01		029002DD
02		D04800A2
03		00000027

Hi Juan,

Please let me know if this register configuration works better on your end. If not, we could possibly take a look at the schematic for your design and determine if there may be something causing an issue there.

Best,

Luke Allen 

Hi Luke,

We tested your register configuration and the result still the same. The yellow signal is CHA and green signal is CHB.

This is our DAC schematic. To test the single mode (CLK1) we removed C226 and R234 so the pin (CLK0/CLK1) is floating. Additionally the C230 value is 1nF.

Regards,

Juan Camilo Peña A.

Juan,

Are those measurements taken directly form the output pin of the DAC? Do you have some circuitry at the output of the DAC? If  so, could you share that schematic as well?

Best,

Luke Allen

Hi Luke, this is the output taken of DAC pins, the previous images showed signals with higher amplitude because of the HW after the DAC.

The yellow signal is IOUTA1, green signal es IOUTA2 and purple is (IOUTA1 - IOUTA2) 

The yellow signal is IOUTB2, green signal es IOUTB1 and purple is (IOUTB2 - IOUTB1) 

We are seeing the glitch on output A. Can you say to us if any thing is wrong on DAC schematic? 

Thanks,

Juan Camilo Peña A.

Hi Juan,

I see no issues with the portion of the schematic you sent me. I am thinking something else on your board may be causing this. Lets try to get a sine wave working first. If you try outputting a sine wave and increasing/decreasing the frequency, how does the glitch change? If you connect the output to a spectrum analyzer when outputting a sine wave, do you see any spurs that are not harmonics? This could help us determine if the glitch is being caused by another signal combining with the output signal of the DAC.

Best,

Luke Allen