Author Topic: Can't get SDO data out of a LTC2402  (Read 659 times)

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Offline RawCodeTopic starter

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Can't get SDO data out of a LTC2402
« on: June 30, 2020, 10:00:20 am »
Hello guys.
I'm quite demoralized.

I'm trying to build something like a source-meter for my thesis work. Everything seems to work, except for the LTC2402. Seriously, it's driving me crazy.
I tied the LTC2402 to a Nucleo-F767ZI according to these schematics:

1013366-0 1013390-1

i.e. CS to PE6, SCK to PG11 and SDO to PA6. I also setted the SPI configuration as follows:

1013370-2

So, according to the LTC2402's datasheet, when CS goes low, SDO goes low too if the conversion is finished, otherwise it stays high. When CS goes high, SDO goes to Hi-Z.
But, anything i do, i can't pull data from the LTC2402. SDO seems to stay in an unknown Hi-Z state, even if CS is low.
I tried to pull-down SDO and SCK to DGND, but nothing changed.
Here the signals at the oscilloscope. CH1 and CH2 represents SDO and SCK. I inverted CH1 and CH2 in a picture. Sometimes i get a "smaller" replica of SCK signal on SDO, sometimes something that seems a GND on SDO, sometimes a very noisy replica of SCK signal on SDO. I handsoldered it to a pcb, so maybe the solder job is not the best, but there is continuity in all signals, even touching the package leads.

1013378-3 1013382-4 1013386-5 1013374-6

Please, can you help me?
 

Offline exe

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Re: Can't get SDO data out of a LTC2402
« Reply #1 on: June 30, 2020, 10:34:17 am »
I'd clean flux, just in case. Also, may be the part is damaged...
 

Offline Giaime

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Re: Can't get SDO data out of a LTC2402
« Reply #2 on: July 02, 2020, 10:30:45 am »
After a quick look, I'd suggest you pull-up SDO instead of pulling it down. Try 10k resistor and let us know.
 

Online SiliconWizard

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Re: Can't get SDO data out of a LTC2402
« Reply #3 on: July 02, 2020, 03:45:56 pm »
Couple thoughts:

- You need to pull SDO to something, because it's in Hi-Z when /CS is high. Leaving it floating is not a good idea. The datasheet suggests pulling it low. You said you tried and it didn't make a difference. I can't believe it didn't. At least when /CS is high, instead of seeing a signal in a typical "hi-z" state, you should see a straight low level. If not, something else is clearly wrong. Maybe your soldering.
- How do you control /CS? Did you take a look at it? Would be interesting to look at it with the scope. Maybe it's actually not controlled properly. This point might be due to an improper software configuration.
 

Offline RawCodeTopic starter

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Re: Can't get SDO data out of a LTC2402
« Reply #4 on: July 03, 2020, 05:31:27 pm »
Hello guys, thanks for all your replies.
After trying everything, i changed the ic and now it works.

My father checked the board in the microscope before changing the ic and he says it was well soldered. So I presume it was kinda faulty.

Luckly enough i had a spare of this ADC.
 


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