SPRS439I – JUNE 2007 – REVISED MARCH 2011
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6.15 On-Chip Analog-to-Digital Converter
Table 6-50. ADC Electrical Characteristics (over recommended operating conditions)
(1)
PARAMETER
DC SPECIFICATIONS
(3)
Resolution
ADC clock
ACCURACY
INL (Integral nonlinearity)
1-12.5 MHz ADC clock (6.25 MSPS)
12.5-25 MHz ADC clock
(12.5 MSPS)
DNL (Differential nonlinearity)
(4)
Offset error
(5) (3)
(6) (3)
(3)
(2)
MIN
12
0.001
TYP
MAX
UNIT
Bits
25
±1.5
±2
±1
MHz
LSB
LSB
LSB
LSB
LSB
LSB
LSB
LSB
–15
–30
–30
±4
±4
(7)
15
30
30
Overall gain error with internal reference
Overall gain error with external reference
Channel-to-channel offset variation
Channel-to-channel gain variation
ANALOG INPUT
Analog input voltage (ADCINx to ADCLO)
ADCLO
Input capacitance
Input leakage current
INTERNAL VOLTAGE REFERENCE
(6)
0
–5
0
10
3
5
±5
1.275
0.525
0.75
50
V
mV
pF
μA
V
V
V
PPM/°C
V
V
V
dB
dB
dB
Bits
dB
V
ADCREFP
- ADCREFP output voltage at the pin based on
internal reference
V
ADCREFM
- ADCREFM output voltage at the pin based on
internal reference
Voltage difference, ADCREFP - ADCREFM
Temperature coefficient
EXTERNAL VOLTAGE REFERENCE
(6)
(8)
V
ADCREFIN
- External reference voltage input on ADCREFIN
pin 0.2% or better accurate reference recommended
ADCREFSEL[15:14] = 11b
ADCREFSEL[15:14] = 10b
ADCREFSEL[15:14] = 01b
1.024
1.500
2.048
67.5
68
–79
10.9
83
AC SPECIFICATIONS
SINAD (100 kHz) Signal-to-noise ratio + distortion
SNR (100 kHz) Signal-to-noise ratio
THD (100 kHz) Total harmonic distortion
ENOB (100 kHz) Effective number of bits
SFDR (100 kHz) Spurious free dynamic range
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
Tested at 25 MHz ADCCLK.
All voltages listed in this table are with respect to V
SSA2
.
ADC parameters for gain error and offset error are only specified if the ADC calibration routine is executed from the Boot ROM. See
for more information.
TI specifies that the ADC will have no missing codes.
1 LSB has the weighted value of 3.0/4096 = 0.732 mV.
A single internal/external band gap reference 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 listed for the internal reference
is inclusive of the movement of the internal bandgap over temperature. Gain error over temperature for the external reference option will
depend on the temperature profile of the source used.
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.
TI recommends using high precision external reference TI part REF3020/3120 or equivalent for 2.048-V reference.
168
Electrical Specifications
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