ZHCSKR7A February 2020 – February 2020 ADS8355
PRODUCTION DATA.
The device has two simultaneous sampling ADCs: ADC_A and ADC_B. ADC_A and ADC_B operate with reference voltages VREF_A and VREF_B present on the REFIO_A and REFIO_B pins, respectively. Decouple the REFIO_A and REFIO_B pins with the REFGND_A and REFGND_B pins, respectively, with 10-µF decoupling capacitors.
As illustrated in Figure 24, the device supports operation either with an internal or external reference source. The reference voltage source is determined by programming the INT_EXT bit of the REF_SEL register. This bit is common to ADC_A and ADC_B.
The default value of the REF_SEL register bit INT_EXT is set to 0. The device ADC_A and ADC_B operate with the external reference voltages provided on the REFIO_A and REFIO_B pins, respectively.
When the REF_SEL register bit INT_EXT is set to 1, the device operates with the internal reference source connected to REFIO_A and REFIO_B. The individual reference voltages can be set independently by programming the REFDAC_A and REFDAC_B values, respectively. For a 2.5-V internal reference, program REFDAC_x with a 0x1FF value..
Figure 25 shows a typical transfer function for the internal REFDAC when the internal reference is enabled.