Hellow. I'm reading data from AD7780. But I can read only once. Help me pls. The PDRST pin is always "ONE".
The differential input voltage range of the AD7780 is equivalent to AIN(+) - AIN(-) = ±VREF/gain.
Given a VREF=1V & gain=128, the part can allow a differential input of AIN(+) - AIN(-) = 7.8mV, hence , if the full-scale output range of your transducer equals 6mV, a VREF of 1V is applicable.
The analog inputs, AIN(+) & AIN(-), can be biased at a certain level, between GND+450mV to AVDD-1.1 @ gain=128, as long as its difference, AIN(+) - AIN(-), would not exceed VREF/gain.
For ex. AIN(+)=2.506V; AIN(-)=2.5V, the differential input voltage would be , 2.506V – 2.5V = 6mV.
To reduce the reference to 1V, external resistors would be needed to attenuate the 5V excitation voltage. These resistors will add some noise. So, the overall noise may increase alittle.
Thanks and Best Regards,
We are looking into this. We'll get back to you as soon as possible.
I have the same reply from ADC:
00 00 00 69
that does it mean?
The operation that you are seeing is correct. When a conversion is available from the AD7780, DOUT/RDY goes low. When the SCLKs are applied to the ADC, the 24-bit conversion is placed on the DOUT line. This is followed by 8 status bits. The data is only output once. After outputting the conversion, the ADC waits until the next conversion is available and then takes DOUT/RDY low again. The serial interface is reset so that the next conversion is output as soon as the SCLK pulses are applied.
Only 32 SCLK pulses are needed (24 for the data and 8 for the status bits). Applying more than 32 SCLK pulses has no affect on the ADC.
Thanks a lot for your reply. It was very helpful for me.
I have got one more question.
I use AD7780 in a weigh scale application. The load cell is arranged in a bridge network and
gives a differential output voltage between its OUT+ and OUT− terminals.
Assuming a 5 V excitation voltage, the full-scale output range from the transducer is 6 mV when the sensitivity
is 1,2 mV/V. The reference for the ADC is 2,5 V. AIN+ and AIN- is about 2,5 V. Gain of ADC is 128.
And 128 x 6 mV = 780 mV.Could it be a reference voltage is 1000 mV or not becasu analog input is 2,5 V?
Is this right --> AIN+ < V ref?
Retrieving data ...