TMS320F2811 datasheet(142/173 Pages) TI

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Electrical Specifications

141

April 2001 − Revised July 2007

SPRS174O

6.31.2

ADC Electrical Characteristics Over Recommended Operating Conditions

Table 6−42. DC Specifications (See Note 1)

PARAMETER

MIN

TYP

MAX

UNIT

Resolution

Bits

ADC clock (See Note 2)

kHz

ADC clock (See Note 2)

MHz

ACCURACY

INL (Integral nonlinearity) (See Note 3)

1−18.75 MHz ADC clock

±1.5

LSB

DNL (Differential nonlinearity) (See Note 3)

1−18.75 MHz ADC clock

±1

LSB

Offset error (See Note 4)

−80

LSB

Overall gain error with internal reference

F281x

−200

200

LSB

Overall gain error with internal reference

(See Note 5)

C281x

−80

LSB

Overall gain error with external reference

(See Note 6)

If ADCREFP−ADCREFM = 1 V

±0.1%

−50

LSB

Channel-to-channel offset variation

±8

LSB

Channel-to-channel Gain variation

±8

LSB

ANALOG INPUT

Analog input voltage (ADCINx to ADCLO)

(See Note 7)

ADCLO

−5

Input capacitance

Input leakage current

±5

µA

INTERNAL VOLTAGE REFERENCE

(See Note 5)

Accuracy, ADCVREFP

1.9

2.1

Accuracy, ADCVREFM

0.95

1.05

Voltage difference, ADCREFP − ADCREFM

Temperature coefficient

PPM/

°C

Reference noise

100

µV

EXTERNAL VOLTAGE REFERENCE (See Note 6)

Accuracy, ADCVREFP

1.9

2.1

Accuracy, ADCVREFM

0.95

1.05

Input voltage difference, ADCREFP − ADCREFM

0.99

1.01

NOTES:

1. Tested at 12.5-MHz ADCCLK

2. If SYSCLKOUT

≤ 25 MHz, ADC clock ≤ SYSCLKOUT/2

3. The INL degrades for frequencies beyond 18.75 MHz − 25 MHz. Applications that require these sampling rates should use a

20K-resistor as bias resistor on the ADCRESEXT pin. This improves overall linearity and typical current drawn by the ADC will

be a few mA more than 24.9 k

Ω bias. The ADC module in C281x devices can operate at 24.9k bias on ADCRESEXT pin for the

full range 1−25MHz

4. 1 LSB has the weighted value of 3.0/4096 = 0.732 mV.

5. A single internal band gap reference (

±5% accuracy) sources both ADCREFP and ADCREFM signals, and hence, these voltages

track together. The ADC converter uses the difference between these two as its reference. The total gain error will be the

combination of the gain error shown here and the voltage reference accuracy (ADCREFP − ADCREFM). A software-based

calibration procedure is recommended for better accuracy. See F2812 ADC Calibration Application Note (literature number

SPRA989) and Section 5.2, Documentation Support, for relevant documents.

6. In this mode, the accuracy of external reference is critical for overall gain. The voltage difference (ADCREFP−ADCREFM) will

determine the overall accuracy.

7. Voltages above VDDA + 0.3 V or below VSS − 0.3 V applied to an analog input pin may temporarily affect the conversion of another

pin. To avoid this, the analog inputs should be kept within these limits.

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