Linux/DAC7568: My output gain is doubled sometimes.

vik

Part Number: DAC7568
Other Parts Discussed in Thread: ADS114S08,

Tool/software: Linux

Hi there..

The output gain of my DAC7568C is doubled occasionally.

I have a ADS114S08 device on the same SPI bus. Once I disable the ADS device in my linux dt, the DAC works normally(no double gain issue).

I checked at the spi lines using a oscilloscope and I verified that the data received by DAC is error free.

There exists another DAC7568C on the same board in a different SPI line which works just fine. Only the first DAC has the gain issue.

I have attached a reference test log file of DAC values on automated reboots with different cases. (about 350 reboots)

Note: In the attached log file, the 1.3V is the correct value and the 2.5V is the incorrect value(doubled gain)

Below is my device-tree entry of the SPI bus in which the DAC & ADS reside.

&ecspi2 {
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_ecspi2>;
// fsl,spi-num-chipselects = <2>;
cs-gpios = <&gpio3 2 GPIO_ACTIVE_LOW>,
<&gpio3 3 GPIO_ACTIVE_LOW>;
status = "okay";

adc114s08_3: adcdev@2 {
compatible = "adcdev-3";
reg = <0>;
spi-max-frequency = <6000000>;
spi-cpha;
gpio-dr = <&gpio3 4 GPIO_ACTIVE_HIGH>;
status = "okay";
};
dac7568_1: dacdev@0 {
compatible = "dacdev-1";
reg = <1>;
spi-max-frequency = <6000000>;
spi-cpha;
gpio-ls = <&gpio3 20 GPIO_ACTIVE_HIGH>;
status = "okay";
};
};

Fullscreen testrep.txt Download

Sun Dec 16 12:38:09 UTC 2018
ADC VALUE: 0x426D => 1.29739833 V

ADC VALUE: 0x424B => 1.29480433 V

ADC VALUE: 0x4267 => 1.29694057 V

ADC VALUE: 0x424E => 1.29503322 V

ADC VALUE: 0x41DD => 1.28641188 V

ADC VALUE: 0x41C0 => 1.28419936 V

ADC VALUE: 0x41F3 => 1.28809035 V

ADC VALUE: 0x41AD => 1.28274965 V

ADC VALUE: 0x41EC => 1.28755629 V

ADC VALUE: 0x424E => 1.29503322 V

ADC VALUE: 0x4233 => 1.29297316 V

ADC VALUE: 0x425A => 1.29594874 V

ADC VALUE: 0x426F => 1.29755092 V

ADC VALUE: 0x4247 => 1.29449916 V

ADC VALUE: 0x4270 => 1.29762721 V

ADC VALUE: 0x4246 => 1.29442286 V

ADC VALUE: 0x423B => 1.29358351 V

ADC VALUE: 0x41D5 => 1.28580153 V

ADC VALUE: 0x41C3 => 1.28442824 V

ADC VALUE: 0x4227 => 1.29205763 V

ADC VALUE: 0x4246 => 1.29442286 V

ADC VALUE: 0x4259 => 1.29587245 V

ADC VALUE: 0x4259 => 1.29587245 V

ADC VALUE: 0x425C => 1.29610133 V

ADC VALUE: 0x4259 => 1.29587245 V

ADC VALUE: 0x41E6 => 1.28709853 V

ADC VALUE: 0x4250 => 1.29518580 V

ADC VALUE: 0x4253 => 1.29541469 V

ADC VALUE: 0x423B => 1.29358351 V

ADC VALUE: 0x423D => 1.29373610 V

ADC VALUE: 0x4270 => 1.29762721 V

ADC VALUE: 0x4264 => 1.29671168 V

ADC VALUE: 0x4264 => 1.29671168 V

ADC VALUE: 0x4270 => 1.29762721 V

ADC VALUE: 0x427B => 1.29846644 V

ADC VALUE: 0x4245 => 1.29434657 V

ADC VALUE: 0x437F => 1.31830323 V

ADC VALUE: 0x423C => 1.29365981 V

ADC VALUE: 0x4249 => 1.29465175 V

ADC VALUE: 0x4236 => 1.29320204 V

ADC VALUE: 0x4254 => 1.29549098 V

ADC VALUE: 0x4253 => 1.29541469 V

ADC VALUE: 0x410F => 1.27069497 V

ADC VALUE: 0x41D0 => 1.28542006 V

ADC VALUE: 0x426C => 1.29732203 V

ADC VALUE: 0x425F => 1.29633021 V

ADC VALUE: 0x4176 => 1.27855349 V

ADC VALUE: 0x424F => 1.29510951 V

ADC VALUE: 0x4271 => 1.29770350 V

ADC VALUE: 0x4266 => 1.29686427 V

ADC VALUE: 0x424A => 1.29472804 V

ADC VALUE: 0x41DA => 1.28618300 V

ADC VALUE: 0x4090 => 1.26100552 V

ADC VALUE: 0x424E => 1.29503322 V

ADC VALUE: 0x41E2 => 1.28679335 V


Sun Dec 16 13:06:38 UTC 2018
POWEROFF & REBOOT

ADC VALUE: 0x4220 => 1.29152358 V
WRITING INTO DAC2 BEFORE DAC1
ADC VALUE: 0x7F1D => 2.48271918 V

ADC VALUE: 0x7EF7 => 2.47982001 V

ADC VALUE: 0x7F2C => 2.48386359 V

ADC VALUE: 0x7ECE => 2.47669196 V

ADC VALUE: 0x7F6A => 2.48859382 V

ADC VALUE: 0x7F30 => 2.48416877 V

ADC VALUE: 0x7F09 => 2.48119330 V

ADC VALUE: 0x7F63 => 2.48805976 V

Sun Dec 16 13:14:04 UTC 2018

WRITING INTO DAC1 BEFORE DAC2
ADC VALUE: 0x8105 => 2.51995111 V

ADC VALUE: 0x8109 => 2.52025628 V

ADC VALUE: 0x80C6 => 2.51514459 V

ADC VALUE: 0x80F7 => 2.51888299 V

ADC VALUE: 0x80E4 => 2.51743340 V

ADC VALUE: 0x80C5 => 2.51506829 V

ADC VALUE: 0x810F => 2.52071404 V

ADC VALUE: 0x80DF => 2.51705194 V

ADC VALUE: 0x8107 => 2.52010369 V

ADC VALUE: 0x8103 => 2.51979852 V

ADC VALUE: 0x7E4F => 2.46700239 V

ADC VALUE: 0x8117 => 2.52132440 V

ADC VALUE: 0x8123 => 2.52223992 V

ADC VALUE: 0x8100 => 2.51956964 V

ADC VALUE: 0x811D => 2.52178216 V

ADC VALUE: 0x80AA => 2.51300836 V

ADC VALUE: 0x7FD6 => 2.49683380 V

ADC VALUE: 0x80EA => 2.51789117 V

ADC VALUE: 0x8116 => 2.52124810 V

ADC VALUE: 0x810E => 2.52063775 V

ADC VALUE: 0x8118 => 2.52140069 V

ADC VALUE: 0x80FB => 2.51918817 V

ADC VALUE: 0x80FB => 2.51918817 V

date
Sun Dec 16 13:25:25 UTC 2018
NOT WRITING INTO DAC2
ADC VALUE: 0x7EF2 => 2.47943854 V

ADC VALUE: 0x7F99 => 2.49217963 V

ADC VALUE: 0x7F26 => 2.48340583 V

ADC VALUE: 0x7F11 => 2.48180366 V

ADC VALUE: 0x7DF9 => 2.46044111 V

ADC VALUE: 0x7EDD => 2.47783637 V

ADC VALUE: 0x7EA3 => 2.47341108 V

ADC VALUE: 0x7F11 => 2.48180366 V

ADC VALUE: 0x7EF4 => 2.47959113 V

ADC VALUE: 0x7D25 => 2.44426632 V

ADC VALUE: 0x7F06 => 2.48096442 V

ADC VALUE: 0x7F29 => 2.48363471 V

ADC VALUE: 0x7E98 => 2.47257185 V

ADC VALUE: 0x7F08 => 2.48111701 V

ADC VALUE: 0x7E55 => 2.46746016 V

ADC VALUE: 0x7F0F => 2.48165107 V

ADC VALUE: 0x7F67 => 2.48836493 V

ADC VALUE: 0x7F10 => 2.48172736 V

Sun Dec 16 13:35:45 UTC 2018
POWERDOWN & REBOOT
ADC VALUE: 0x811A => 2.52155328 V

Sun Dec 16 13:39:11 UTC 2018
RMMOD DAC2 & RESTARTS
ADC VALUE: 0x7F4A => 2.48615241 V

ADC VALUE: 0x7EEE => 2.47913337 V

ADC VALUE: 0x7F17 => 2.48226142 V

ADC VALUE: 0x7E16 => 2.46265364 V

ADC VALUE: 0x7F2D => 2.48393989 V

ADC VALUE: 0x7B48 => 2.40787363 V

ADC VALUE: 0x7EEF => 2.47920966 V

ADC VALUE: 0x7E43 => 2.46608686 V

ADC VALUE: 0x7F5A => 2.48737311 V

Sun Dec 16 13:45:14 UTC 2018
POWERDOWN & RESTARTS
ADC VALUE: 0x811E => 2.52185845 V

ADC VALUE: 0x8000 => 2.50003815 V

Sun Dec 16 13:51:33 UTC 2018
DISABLING ADC3
ADC VALUE: 0x4234 => 1.29304945 V

ADC VALUE: 0x426A => 1.29716945 V

ADC VALUE: 0x40B4 => 1.26375210 V

Sun Dec 16 13:58:24 UTC 2018
POWEROFF & REBOOT
ADC VALUE: 0x4370 => 1.31715882 V

ADC VALUE: 0x8000 => 2.50003815 V

ADC VALUE: 0x420F => 1.29022658 V

ADC VALUE: 0x425F => 1.29633021 V

ADC VALUE: 0x4244 => 1.29427028 V

ADC VALUE: 0x421B => 1.29114211 V

ADC VALUE: 0x4267 => 1.29694057 V

ADC VALUE: 0x41DF => 1.28656447 V

ADC VALUE: 0x41EE => 1.28770888 V

ADC VALUE: 0x4260 => 1.29640651 V

ADC VALUE: 0x4273 => 1.29785609 V

ADC VALUE: 0x4254 => 1.29549098 V

ADC VALUE: 0x4239 => 1.29343092 V

ADC VALUE: 0x4263 => 1.29663539 V

ADC VALUE: 0x4247 => 1.29449916 V

ADC VALUE: 0x423F => 1.29388869 V

ADC VALUE: 0x4105 => 1.26993203 V

ADC VALUE: 0x425F => 1.29633021 V

ADC VALUE: 0x426A => 1.29716945 V

ADC VALUE: 0x4254 => 1.29549098 V

ADC VALUE: 0x4079 => 1.25925076 V

ADC VALUE: 0x425D => 1.29617763 V

ADC VALUE: 0x425F => 1.29633021 V

ADC VALUE: 0x426F => 1.29755092 V

ADC VALUE: 0x4263 => 1.29663539 V

ADC VALUE: 0x4275 => 1.29800868 V

ADC VALUE: 0x40AC => 1.26314175 V

ADC VALUE: 0x423B => 1.29358351 V

ADC VALUE: 0x427C => 1.29854274 V

Sun Dec 16 14:12:54 UTC 2018

WRITING DAC2 & DAC1

ADC VALUE: 0x4106 => 1.27000833 V

ADC VALUE: 0x4247 => 1.29449916 V

ADC VALUE: 0x43BB => 1.32288086 V

ADC VALUE: 0x425D => 1.29617763 V

ADC VALUE: 0x423A => 1.29350722 V

ADC VALUE: 0x424F => 1.29510951 V

ADC VALUE: 0x4267 => 1.29694057 V

ADC VALUE: 0x424F => 1.29510951 V

ADC VALUE: 0x4265 => 1.29678798 V

ADC VALUE: 0x4243 => 1.29419398 V

ADC VALUE: 0x4280 => 1.29884791 V

>ADC VALUE: 0x6A9 => 0.13008316 V

ADC VALUE: 0x4193 => 1.28076601 V

ADC VALUE: 0x4253 => 1.29541469 V

>ADC VALUE: 0x6AA => 0.13015945 V

ADC VALUE: 0x41BA => 1.28374147 V

ADC VALUE: 0x424D => 1.29495692 V

ADC VALUE: 0x43B8 => 1.32265198 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43B9 => 1.32272828 V

ADC VALUE: 0x43BB => 1.32288086 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43B9 => 1.32272828 V

Sun Dec 16 14:49:03 UTC 2018
ENABLING ADC3
ADC VALUE: 0x43B8 => 1.32265198 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43BB => 1.32288086 V

ADC VALUE: 0x43B8 => 1.32265198 V

ADC VALUE: 0x43BB => 1.32288086 V

ADC VALUE: 0x43B9 => 1.32272828 V

ADC VALUE: 0x43BB => 1.32288086 V

ADC VALUE: 0x43B9 => 1.32272828 V

ADC VALUE: 0x43BB => 1.32288086 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43BC => 1.32295716 V

ADC VALUE: 0x43BB => 1.32288086 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43BB => 1.32288086 V

ADC VALUE: 0x43B9 => 1.32272828 V

Sun Dec 16 14:58:43 UTC 2018
POWEROFF & RESTART
ADC VALUE: 0x8227 => 2.54207659 V

ADC VALUE: 0x8000 => 2.50003815 V

ADC VALUE: 0x8228 => 2.54215288 V

Sun Dec 16 15:05:36 UTC 2018
RMMOD ADC3
ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43B9 => 1.32272828 V

ADC VALUE: 0x43B8 => 1.32265198 V

ADC VALUE: 0x43BA => 1.32280457 V

Sun Dec 16 15:09:34 UTC 2018
POWEROFF & REBOOT
ADC VALUE: 0x43B8 => 1.32265198 V

ADC VALUE: 0x8000 => 2.50003815 V

ADC VALUE: 0x43B9 => 1.32272828 V

ADC VALUE: 0x43B8 => 1.32265198 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43B7 => 1.32257569 V

ADC VALUE: 0x43B8 => 1.32265198 V

ADC VALUE: 0x43B8 => 1.32265198 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43B9 => 1.32272828 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43B9 => 1.32272828 V

ADC VALUE: 0x43B8 => 1.32265198 V

ADC VALUE: 0x43B7 => 1.32257569 V

ADC VALUE: 0x43B8 => 1.32265198 V

ADC VALUE: 0x43B7 => 1.32257569 V

ADC VALUE: 0x43B9 => 1.32272828 V

ADC VALUE: 0x8000 => 2.50003815 V

ADC VALUE: 0x43B8 => 1.32265198 V

ADC VALUE: 0x43B9 => 1.32272828 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43B9 => 1.32272828 V

ADC VALUE: 0x43B8 => 1.32265198 V

ADC VALUE: 0x43B7 => 1.32257569 V

ADC VALUE: 0x43B9 => 1.32272828 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43B8 => 1.32265198 V

ADC VALUE: 0x43B9 => 1.32272828 V

ADC VALUE: 0x43B8 => 1.32265198 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43B8 => 1.32265198 V

ADC VALUE: 0x43B8 => 1.32265198 V

ADC VALUE: 0x43B9 => 1.32272828 V

ADC VALUE: 0x43B9 => 1.32272828 V

ADC VALUE: 0x43B8 => 1.32265198 V

ADC VALUE: 0x43B9 => 1.32272828 V

ADC VALUE: 0x43B8 => 1.32265198 V

ADC VALUE: 0x43B9 => 1.32272828 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43B8 => 1.32265198 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43B8 => 1.32265198 V

ADC VALUE: 0x43B8 => 1.32265198 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43B7 => 1.32257569 V

ADC VALUE: 0x43B9 => 1.32272828 V

ADC VALUE: 0x43B9 => 1.32272828 V

ADC VALUE: 0x43B9 => 1.32272828 V

Sun Dec 16 15:36:36 UTC 2018
DISABLING ADC3 FROM DTB
ADC VALUE: 0x43BB => 1.32288086 V

ADC VALUE: 0x43B8 => 1.32265198 V

ADC VALUE: 0x43B9 => 1.32272828 V

ADC VALUE: 0x43BB => 1.32288086 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43BB => 1.32288086 V

ADC VALUE: 0x43BB => 1.32288086 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43B9 => 1.32272828 V

ADC VALUE: 0x43B8 => 1.32265198 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43BB => 1.32288086 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43B9 => 1.32272828 V

ADC VALUE: 0x43BB => 1.32288086 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43BB => 1.32288086 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43BB => 1.32288086 V

ADC VALUE: 0x43BB => 1.32288086 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43BB => 1.32288086 V

ADC VALUE: 0x43B9 => 1.32272828 V

ADC VALUE: 0x43BB => 1.32288086 V

ADC VALUE: 0x43BC => 1.32295716 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43BB => 1.32288086 V

ADC VALUE: 0x43BC => 1.32295716 V

Sun Dec 16 16:00:57 UTC 2018
ENABLED ADC3 IN DTB BUT RMMMOD ADC3
ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43B8 => 1.32265198 V

ADC VALUE: 0x43B9 => 1.32272828 V

ADC VALUE: 0x43B9 => 1.32272828 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43BC => 1.32295716 V

ADC VALUE: 0x43BC => 1.32295716 V

ADC VALUE: 0x43B9 => 1.32272828 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43BA => 1.32280457 V

ADC VALUE: 0x43B8 => 1.32265198 V

ADC VALUE: 0x43B9 => 1.32272828 V

Please find the schematic for reference

over 7 years ago

0 Uttam Sahu over 7 years ago

TI__Genius 14220 points

Hi Vik,

Thank you for your query. I am looking into it. I will get back by tomorrow.

Regards,
Uttam Sahu
Applications Engineer, Precision DACs

0 vik over 7 years ago in reply to Uttam Sahu

Intellectual 500 points

Hi Uttam, any updates on how the DAC double gain issue might have occured??

0 Uttam Sahu over 7 years ago in reply to vik

TI__Genius 14220 points

Hi Vik,

My apologies for being unresponsive for so long. I was completely occupied last couple of weeks. I have a couple of questions:

1. When you disable the ADC, which signals get isolated from the DAC? Is it only SPI?
2. Have you shared the DAC reference with ADC and is it getting loaded?

Regards,
Uttam

0 Uttam Sahu over 7 years ago in reply to Uttam Sahu

TI__Genius 14220 points

Hi Vik,

Do you have any update on this?

Regards,
Uttam

0 vik over 7 years ago in reply to Uttam Sahu

Intellectual 500 points

Please find your answers inline:
1. I disable the ADC from the device tree only(but the ADC is connected physically on the same SPI bus) so no signals will be isolated but the ADC will not be functional. Yes both the devices(ADC & DAC) are only SPI based.
2. I am using internal ref 2.5 generated from the ADC chip. For the DAC, I am using 5V ref.
The problem is temporarily fixed by loading the DAC drivers first followed by the ADC driver. But please help me find a final fix.

0 Uttam Sahu over 7 years ago in reply to vik

TI__Genius 14220 points

Hi Vik,

Looks like the ADC driver is is not closing properly or something creating some contention on the SPI bus.

If you could share a scope shot of wht is happening when you load the DAC driver first and then ADC, and vice-versa, We might be able to find the root cause.

Regards,
Uttam

0 Kevin Duke over 7 years ago in reply to Uttam Sahu

TI__Mastermind 46290 points

Hello Vik,

Do you have any updates for Uttam on this thread?

0 vik over 7 years ago in reply to Kevin Duke

Intellectual 500 points

sorry I was not working on this task since I have been assigned another project. But I would like to update and fix this issue as well.

0 vik over 7 years ago in reply to Uttam Sahu

Intellectual 500 points

Hi uttam,
I had checked the spi waveform when talking to the dac and it seems ok. I will try to get a digital oscilloscope and capture a image file to show you the same. Please give me some time.

0 Uttam Sahu over 7 years ago in reply to vik

TI__Genius 14220 points

Sure. Please ping us when you get some update.

Regards,
Uttam

0 vik over 7 years ago in reply to Uttam Sahu

Intellectual 500 points

I figured the root cause to this issue. It was 5V enable gpio!

There is a seperate power enable GPIO pin to enable the 5V supply to ADCs and DACs on board coming from an i2c based io-expander.

The problem is the DACs and ADCs are initilized before the 5V is enabled,(hence the partial functionality) so this is totally a board design problem.

Now the ADCs and DACs work flawlessly. This thread could be closed since there is no productive information or any issues related to TI chips.

Thank you so much for the help.

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Linux/DAC7568: My output gain is doubled sometimes.