Hi,
I am using ADS1255 to measure a resistor bridge, each arm is about 10K. I need to use the input buffer of ADS 1255 to increase the input impedance. Bus there's no input bias current and input offset current and there temperature coefficient values in the datasheet. Could you find these datas for me? thank you.
Hello Danny,
Welcome to the TI E2E community.
The ADS1255 input buffer is a chopper stabilized amplifier, and the average differential input current is dominated by the input switching effects of the amplifier input structure. This average input current is proportional to the input voltage, and is specified as an equivalent input resistance. This effective input resistance is also dependent on the input clock frequency, CLKIN, and the data rate, per Table 7.
If f-CLKIN is not equal to 7.68MHz, then scale the effective input resistance in Table 7. For example, if the input clock frequency is 1MHz, and the data rate register setting is 60sps (actual data rate with CLKIN=1MHz will be 60*1/7.68=7.8125sps in this example), then Zeff will be 7.68MHz/1MHz*40Meg=307.2MegOhm.
We do not have any data on variation over temperature. If these specifications are important, the newer ADS1260 includes these types of specifications.
Regards,
Keith Nicholas
Precision ADC Applications
