JAJSH44C April 2011 – March 2019 UCD90120A
The UCD90120A uses a 12-bit ADC and an internal 2.5-V reference (VREF) to convert MON pin inputs into digitally reported voltages. The least significant bit (LSB) value is VLSB = VREF/2N where N = 12, resulting in a VLSB = 610 μV. The error in the reported voltage is a function of the ADC linearity errors and any variations in VREF. The total unadjusted error (ETUE) for the UCD90120A ADC is ±5 LSB, and the variation of VREF is ±0.5% between 0°C and 125°C and ±1% between –40°C and 125°C. VTUE is calculated as VLSB × ETUE. The total reported voltage error is the sum of the reference-voltage error and VTUE. At lower monitored voltages, VTUE dominates reported error, wheereas at higher monitored voltages, the tolerance of VREF dominates the reported error. Reported error can be calculated using Equation 3, where REFTOL is the tolerance of VREF, VACT is the actual voltage being monitored at the MON pin, and VREF is the nominal voltage of the ADC reference.
From Equation 3, for temperatures between 0°C and 125°C, if VACT = 0.5 V, then RPTERR = 1.11%. If VACT = 2.2 V, then RPTERR = 0.64%. For the full operating temperature range of –40°C to 125°C, if VACT = 0.5 V, then RPTERR = 1.62%. If VACT = 2.2 V, then RPTERR = 1.14%.