AFS090 datasheet(143/334 Pages) MICROSEMI

143 / 334 page

Fusion Family of Mixed Signal FPGAs

R e visio n 2

2 - 127

Similarly,

Min. Output Voltage = (Max. Negative input offset) + (Input Voltage x Max. Negative Channel Gain)

= (–88 mV) + (5 V x 0.96) = 4.712 V

Calculating Accuracy for a Calibrated Analog Channel

Formula

For a given prescaler range, EQ 31 gives the output voltage.

Output Voltage = Channel Error in V + Input Voltage

EQ 31

where

Channel Error in V = Total Channel Error in LSBs x Equivalent voltage per LSB

Example

Input Voltage = 5 V

Chosen Prescaler range = 8 V range

Refer to Table 2-52 on page 2-125.

Max. Output Voltage = Max. Positive Channel Error in V + Input Voltage

Max. Positive Channel Error in V = (6 LSB) × (8 mV per LSB in 10-bit mode) = 48 mV

Max. Output Voltage = 48 mV + 5 V = 5.048 V

Similarly,

Min. Output Voltage = Max. Negative Channel Error in V + Input Voltage = (–48 mV) + 5 V = 4.952 V

Calculating LSBs from a Given Error Budget

Formula

For a given prescaler range,

LSB count = ± (Input Voltage × Required % error) / (Equivalent voltage per LSB)

Example

Input Voltage = 3.3 V

Required error margin= 1%

Refer to Table 2-52 on page 2-125.

Equivalent voltage per LSB = 16 mV for a 16V prescaler, with ADC in 10-bit mode

LSB Count = ± (5.0 V × 1%) / (0.016)

LSB Count = ± 3.125

Equivalent voltage per LSB = 8 mV for an 8 V prescaler, with ADC in 10-bit mode

LSB Count = ± (5.0 V × 1%) / (0.008)

LSB Count = ± 6.25

The 8 V prescaler satisfies the calculated LSB count accuracy requirement (see Table 2-52 on

page 2-125).

AFS090 Datasheet(PDF) 143 Page - Microsemi Corporation