C8051F360 datasheet(53/288 Pages) SILABS

53 / 288 page

Rev. 1.0

C8051F360/1/2/3/4/5/6/7/8/9

5.3.3. Settling Time Requirements

When the ADC0 input configuration is changed (i.e., a different AMUX0 selection is made), a minimum

tracking time is required before an accurate conversion can be performed. This tracking time is determined

by the AMUX0 resistance, the ADC0 sampling capacitance, any external source resistance, and the accu-

racy required for the conversion. In low-power tracking mode, three SAR clocks are used for tracking at the

start of every conversion. For most applications, these three SAR clocks will meet the minimum tracking

time requirements.

Figure 5.5 shows the equivalent ADC0 input circuits for both Differential and Single-ended modes. Notice

that the equivalent time constant for both input circuits is the same. The required ADC0 settling time for a

given settling accuracy (SA) may be approximated by Equation 5.1. When measuring the Temperature

Sensor output or VDD with respect to GND, RTOTAL reduces to RMUX. See Table 5.1 for ADC0 minimum

settling time requirements.

Equation 5.1. ADC0 Settling Time Requirements

-------

⎝⎠

⎛⎞ R

TOTALCSAMPLE

Where:

SA is the settling accuracy, given as a fraction of an LSB (for example, 0.25 to settle within 1/4 LSB)

t is the required settling time in seconds

RTOTAL is the sum of the AMUX0 resistance and any external source resistance.

n is the ADC resolution in bits (10).

MUX = 5k

Input= RMUX * CSAMPLE

MUX = 5k

SAMPLE = 5pF

MUX Select

Differential Mode

Px.x

MUX = 5k

SAMPLE = 5pF

Input= RMUX * CSAMPLE

MUX Select

Single-Ended Mode

Px.x

Figure 5.5. ADC0 Equivalent Input Circuits

C8051F360 Datasheet(PDF) 53 Page - Silicon Laboratories