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SPRS174S – APRIL 2001 – REVISED MARCH 2011
6.30.2 ADC Electrical Characteristics Over Recommended Operating Conditions
Table 6-44. DC Specifications
(1)
PARAMETER
Resolution
ADC clock
(2)
ACCURACY
INL (Integral nonlinearity)
Offset error
(4)
(3)
MIN
12
1
TYP
MAX
UNIT
Bits
kHz
25
1–18.75 MHz ADC clock
1–18.75 MHz ADC clock
–80
F281x
C281x
If ADCREFP – ADCREFM = 1 V ± 0.1%
–200
–80
–50
±8
±8
ANALOG INPUT
0
–5
0
10
3
INTERNAL VOLTAGE REFERENCE
(5)
1.9
0.95
2
1
1
50
100
EXTERNAL VOLTAGE REFERENCE
(6)
MHz
LSB
LSB
LSB
LSB
LSB
LSB
LSB
±1.5
±1
80
200
80
50
DNL (Differential nonlinearity)
(3)
Overall gain error with internal reference
(5)
Overall gain error with external reference
(6)
Channel-to-channel offset variation
Channel-to-channel Gain variation
Analog input voltage (ADCINx to ADCLO)
(7)
ADCLO
Input capacitance
Input leakage current
Accuracy, ADCV
REFP
Accuracy, ADCV
REFM
Voltage difference, ADCREFP – ADCREFM
Temperature coefficient
Reference noise
Accuracy, ADCV
REFP
Accuracy, ADCV
REFM
Input voltage difference, ADCREFP – ADCREFM
(1)
(2)
(3)
(4)
(5)
3
5
±5
2.1
1.05
V
mV
pF
µA
V
V
V
PPM/°C
µV
1.9
0.95
0.99
2
1
1
2.1
1.05
1.01
V
V
V
(6)
(7)
Tested at 12.5-MHz ADCCLK.
If SYSCLKOUT
≤
25 MHz, ADC clock
≤
SYSCLKOUT/2.
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-kΩ bias. The ADC module in C281x devices can operate at 24.9k bias on ADCRESEXT pin for the full range 1–25 MHz.
1 LSB has the weighted value of 3.0/4096 = 0.732 mV.
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 the
F2810, F2811, and F2812 ADC Calibration Application Report
(literature number
and
Documentation Support, for relevant documents.
In this mode, the accuracy of external reference is critical for overall gain. The voltage difference (ADCREFP – ADCREFM) will
determine the overall accuracy.
Voltages above V
DDA
+ 0.3 V or below V
SS
– 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.
Copyright © 2001–2011, Texas Instruments Incorporated
Electrical Specifications
143
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