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MCP3561 gain not working

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mrguen
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2020/09/09 03:12:18 (permalink)
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MCP3561 gain not working

Hello,
 
I am testing the MCP3561 24 bits ADC. The gain should be programmable 0.33/1/2/4/8/16 . I used a 1 KHz signal, sampled at OSR = 64 i.e. 16 MHz (external) clock / 4 / 64 = 62.5 KHz
 
What I experiment is
 
  • When programming gains 4/8/16: the ADC output is totally saturated (constant value) no matter the amplitude of the input signal.
  • When programming gains 0.33/1/2 the effective gain is half the programmed gain. So a 3V pp signal with gain "1" results in the equivalent of 1.5V pp coded on 24 bits.
 
I used a standard circuit as presented in the datasheet (Figure 7-1 REFIN+ = AVDD, REFIN- = AGND) but realize that the signal is coded on 24 bits signed. It can be within +/- VREF. So I wonder if REFIN- should be set to 1/2 AVDD with REFIN+ = AVDD?
post edited by mrguen - 2020/09/11 19:39:04
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    bbawkon
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    Re: MCP3561 gain not working 2020/09/17 14:29:59 (permalink)
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    I've used that part.  It works correctly.  Something is wrong with your setup.
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    mrguen
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    Re: MCP3561 gain not working 2020/09/21 06:39:57 (permalink)
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    Hello bbawkon,
     
    Yes, possibly I will try another setting of REFIN+ and REFIN-.
     
    Another problem is that when I use continuous conversion mode in MUX mode to convert CH0, I get the correct data rate clock. That is 62.5 KHz for 8 MHz external clock with OSR 32. But when using SCAN mode to scan CH0 then CH1, the data rate clock does not go above 20 KHz, no matter the OSR setting and with TDLY_SCAN to 0 and TIMER to 0.
    The setting is 1) IRQ output to the MCU. 2) Then the MCU reads ACDATA. All interrupts are catched. I see with the logic analyzer that everything is alright. But the data rate stays the same either using OSR 64 or OSR 32 ~ 20 KHz
     
    Did you get faster data rate in continuous SCAN mode no delay?
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