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Original question:

ADS1220EVM: Underdstand ADC PRo software data using ADS1220EVM kit

ADS1220EVM: ADC Pro EVM kit Jumper Kit setting + ADC Pro GUI Setting explnation

Minesh Darji
Prodigy 140 points
Part Number: ADS1220EVM
Other Parts Discussed in Thread: ADS1220,

Hi,

I want to know/confirm that, If I want to give 5V Supply to my Load cell,

Then I need to short jumper connection of ADS1220 EVM kit,

1) JP1 (which is connected to AVDD)

2) JP2 ((which is connected to GND)

What's difference between JP1& JP2 jumper condition in Open  & Close condition?

I also want to understand ADC Pro GUI I/O function, like Low Side power switch, BCS, Temp, Buffer disable.

Also about Current Ref - IDAC magnitude, IDAC 1 Routing, IDAC 2 Routing.

If we select internal Ref then It will be 3.3V or 5V???

Please help to reply soon if possible.

Thanks,

Minesh

  • 0
    TI__Guru** 113765 points

    Hi Minesh,

    I would highly recommend reviewing the contents of the ADS1220 datasheet and the ADS1220EVM user's guide. For example, at the end of the ADS1220EVM user's guide is the board schematic.

    In the ADS1220 datasheet you will see that the ADS1220 can be connected to a variety of sensors.  Sometimes the sensor is excited by a voltage such as a load cell or thermistor while some other sensors, such as an RTD, can be excited by a current source.  For a load cell application you can review the bridge application circuit in section 9.2.3.  To achieve the lowest noise and drift, you should make the measurement ratiometric whereby the same source is used to establish the reference and excite the sensor.

    To achieve the largest dynamic range of the bridge measurement, you would use 5V for AVDD and for excitation of the bridge.  The ADS1220EVM allows you to use the USB 5V power as the 5V source.  You would do this by setting jumper JP3 to the 5V setting.  Jumper JP1 allows you to use the same 5V source to excite the bridge (EXC+).  The excitation return path would go to GND (AVSS) and can be done in one of two ways.  One way is to directly connect the EXC- to GND by attaching jumper JP2.  The second method is to use the low-side switch internal to the ADS1220 which is illustrated in Figure 82 of the ADS1220 datasheet.  You must also use the correct settings for the reference and reference voltage in the Current & Ref tab.  In this case you should choose the External Using AIN0:AIN3 input.  Also change the VREF value to 5V.  You are not using the IDAC current sources, so these should remain off.

    In the I/O Config tab, set the MUX to AIN1:AIN2, the Mode should be Normal.  If you select the Low-Power mode, this operates the ADS1220 in duty-cycle mode.  Please see the ADS1220 datasheet about duty-cycle mode.  The FIR Filter will only work at 20sps (Normal mode) or 5sps (duty-cycle or Low-Power mode).

    Do not disable the buffer.  This mode will bypass the PGA and limit the gain range to 4 or less.  For bridge measurements you will want to keep the buffer enabled and use the highest possible PGA Gain of 128.

    The BCS (burnout current sources) is used primarily for thermocouples where you are looking to see if the thermocouple wire opens.  Do not use this mode.

    The Temp button selects the internal temperature sensor.  See the ADS1220 datasheet for information regarding the temp sensor.

    The Low Side Power Switch allows the excitation to break when in power-down mode when the ADC is not converting.  This button would be selected if JP2 is not connected to ground.  This button would enable the low-side switch to close to AVSS to complete the excitation path.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 140 points

    Hi BOB,

    Sorry for late reply.

    Sincerely apprecaited and very much thanks for your such details explanation.

    I have more one concern - I'm using 5V excitation voltage for my load cell application through USB 5V power as the 5V source, by setting jumper JP3 to the 5V setting.

    My ADC Pro setting is as below

    GUI Configuration : 

    • PGA gain: 128
    • Data Rate : 5 sps
    • MUX channel : AIN1:AIN2
    • Power Mode : Low Power
    • FIR Filter : Simulatneous 50/60Hz Rejection
    • Block Size : 1500
    • Units : Codes/Counts
    • JP3 : 5V

    Based on my above setting , Can you help me to advice to select RC 1st order Low pass filter component value.

    Currently, I'm using R5 & R6 as 1Kohm instead of 0 Ohm to remove instantaneous spike.

    C3 & C5 : 104 pf

    C4 & C32 : 100nF

    Based on above setting still having some more noise spike.

    So I want to get your advice for design modification - LPF section to remove noise/spikes. Please advice.

    Thanks,

    Minesh

  • 0 in reply to Minesh Darji
    TI__Guru** 113765 points

    Hi Minesh,

    According to the values you have given me the cutoff frequency for the analog inputs is about 800Hz. This value seems reasonable.  So when you say you see an instantaneous spike, what does this look like?  Can you send me a screen shot of what you are seeing?

    Keep in mind that not all energy from an instantaneous event will be filtered out using simply an RC filter.  Also, any noise leakage will be gained by 128.  The settings you are using is to take one sample at 20sps (50ms) then sit idle for 3 conversion periods (150ms).  Any instantaneous event would have to happen within the conversion period being measured.

    To get a better understanding of the event, it may be better to capture the data in normal mode and 20sps so that the ADC is continuously converting.  Perhaps an FFT plot of the data would give us better information.

    Best regards,

    Bob B