Datasheet

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SBAS124C − DECEMBER 1999 − REVISED DECEMBER 2005
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5
ELECTRICAL CHARACTERISTICS
For Internal Functions
(1)
, −40°C ≤ T
A
≤ 85°C, V
DD
= 5 V, BUFIN = 2.5 V (using external reference), 2.5-MHz CCLK and 2.5-MHz SCLK (unless
otherwise noted).
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
Multiplexer
On resistance 100 Ω
Off resistance 1 GΩ
Off channel leakage
On channel = 5.2 V,
Off channel = 0 V
V
LNx
= 5.2 V 100 pA
Off channel leakage
current
On channel = 0 V,
Off channel = 5.2 V
100 pA
On channel leakage
On channel = 5.2 V,
Off channel = 0 V
100 pA
On channel leakage
current
On channel = 0 V,
Off channel = 5.2 V
100 pA
PGA Amplifier
Input capacitance
(2)
4 to 9.7 pF
Input impedance
(2)
Common mode 6 MΩ
Input impedance
(2)
Differential 7 MΩ
Offset voltage 100 µV
Small signal bandwidth 5/Gain MHz
Settling time
G = 1 0.3 µs
Settling time
G = 20 6.4 µs
Analog-To-Digital Converter DC Characteristics
Resolution 12 Bits
Integral linearity error ±0.5 LSB
Differential linearity error ±0.5 LSB
No missing codes 12 Bits
Offset error REFIN = 2.5 V ±0.5 LSB
Full-scale (gain) error ±0.02 %
Common mode rejection, RTI of A/D 80 dB
Power supply rejection, RTI of ADS7870 External reference, V
DD
= 5 V ±10% 60 dB
PGA Plus A/D Converter Sampling Dynamics f
CCLK
= 2.5 MHz, DF = 1
Throughput rate 48 CCLK cycles 52 kHz
Conversion time 12 CCLK cycles 4.8 µs
Acquisition time 28 CCLK cycles 9.6 µs
Auto zero time 8 CCLK cycles 3.2 µs
Aperture delay 36 CCLK cycles 12.8 µs
Small signal bandwidth 5 MHz
Step response 1 Complete Conversion Cycle
(1)
The specifications for the total system are overall analog input to digital output specifications. The specifications for internal functions indicate
the performance of the individual functions in the ADS7870.
(2)
The ADS7870 uses switched capacitor techniques for the programmable gain amplifier and A/D converter. A characteristic of such circuits is that
the input capacitance at any selected LNx pin changes during the conversion cycle.