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ADS1258: ADS1258

Meir Yerushalmi
Prodigy 65 points
Part Number: ADS1258

Tool/software:

Hi

We have design based on ADS1258

We want to add external protection to ADC input for Overload\Overvoltage Protection

As the data sheet suggest in P.41 to add  BAT54SWTI to ADC Input lines

BAT54SWTI  Spec :

How this diode with V_Forward  (~400mV) and Reverse  protect ADC input ports ?

We have input signal of  -4V to 4V in the ADC Input 

BAT54SW Seems not let signal above and below ± 1000mV go into the ADC 

Should we use  2 Zener diode with ~4.3V  like  BZX84C4V3S-7-F for over voltage protection ?

Data sheet :  https://www.diodes.com/assets/Datasheets/ds30108.pdf

Thanks in advance

  • 0
    TI__Mastermind 39970 points

    Hello Meir,

    The suggested protection input limits the voltage at the ADC input to within a diode drop (approximately 300mV) below AVSS and above AVDD.  If you are using +/-2.5V bipolar supplies, the maximum voltage on the ADC inputs is then limited to +/-2.8V.

    The ADS1258 can only measure input voltages within the range of the power supply rails, or up to +/-2.5V when using bipolar supplies.  If using a single 5V supply (AVDD=5V, AVSS=0V), then the input voltage range is limited from 0V to 5V.  

    In either case above, if you need to measure a single-ended input voltage of +/-4.096V, then you will need to reduce this signal level to within the recommended voltage range of the ADC inputs.  Figure 67 in the datasheet shows how to do this with +/-10V inputs; you would only need to adjust the resistor values for +/-4V full scale input.

    You could use zener diodes, but these will leak more current and cause measurement errors.  The Schottky diodes work very well to protect the ADC inputs with little effect on measurement accuracy.

    Regards,
    Keith Nicholas
    Precision ADC Applications