DDC
112
®
DDC112
DD
C11
2
®
SBAS085B – JANUARY 2000 – REVISED OCTOBER 2004
Dual Current Input 20-Bit
ANALOG-TO-DIGITAL CONVERTER
FEATURES
q
MONOLITHIC CHARGE MEASUREMENT A/D
CONVERTER
q
DIGITAL FILTER NOISE REDUCTION:
3.2ppm, rms
q
INTEGRAL LINEARITY:
±
0.005% Reading
±
0.5ppm FSR
q
HIGH PRECISION, TRUE INTEGRATING FUNC-
TION
q
PROGRAMMABLE FULL-SCALE
q
SINGLE SUPPLY
q
CASCADABLE OUTPUT
DESCRIPTION
The DDC112 is a dual input, wide dynamic range, charge-
digitizing analog-to-digital (A/D) converter with 20-bit resolu-
tion. Low-level current output devices, such as photosensors,
can be directly connected to its inputs. Charge integration is
continuous as each input uses two integrators; while one is
being digitized, the other is integrating.
For each of its two inputs, the DDC112 combines current-to-
voltage conversion, continuous integration, programmable
full-scale range, A/D conversion, and digital filtering to achieve
a precision, wide dynamic range digital result. In addition to
the internal programmable full-scale ranges, external integrat-
ing capacitors allow an additional user-settable full-scale
range of up to 1000pC.
To provide single-supply operation, the internal A/D converter
utilizes a differential input, with the positive input tied to V
REF
.
When the integration capacitor is reset at the beginning of
each integration cycle, the capacitor charges to V
REF
. This
charge is removed in proportion to the input current. At the
end of the integration cycle, the remaining voltage is com-
pared to V
REF
.
The high-speed serial shift register which holds the result of
the last conversion can be configured to allow multiple DDC112
units to be cascaded, minimizing interconnections. The
DDC112 is available in an SO-28 or TQFP-32 package and is
offered in two performance grades.
V
REF
DV
DD
DGND
APPLICATIONS
q
q
q
q
q
q
DIRECT PHOTOSENSOR DIGITIZATION
CT SCANNER DAS
INFRARED PYROMETER
PRECISION PROCESS CONTROL
LIQUID/GAS CHROMATOGRAPHY
BLOOD ANALYSIS
Protected by US Patent #5841310
AV
DD
CAP1A
CAP1A
IN1
CAP1B
CAP1B
CAP2A
CAP2A
IN2
CAP2B
CAP2B
Dual
Switched
Integrator
Dual
Switched
Integrator
AGND
CHANNEL 1
DCLK
DVALID
DXMIT
DOUT
DIN
RANGE2
RANGE1
RANGE0
∆Σ
Modulator
Digital
Filter
Digital
Input/Output
CHANNEL 2
Control
TEST
CONV
CLK
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All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.
Copyright © 2000-2004, Texas Instruments Incorporated
www.ti.com
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