®
D
D
C1
DDC112
12
D
®
D
C
11
2
SBAS085B – JANUARY 2000 – REVISED OCTOBER 2004
Dual Current Input 20-Bit
ANALOG-TO-DIGITAL CONVERTER
FEATURES
DESCRIPTION
ꢀ MONOLITHIC CHARGE MEASUREMENT A/D
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.
CONVERTER
ꢀ DIGITAL FILTER NOISE REDUCTION:
3.2ppm, rms
ꢀ INTEGRAL LINEARITY:
±0.005% Reading ±0.5ppm FSR
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.
ꢀ HIGH PRECISION, TRUE INTEGRATING FUNC-
TION
ꢀ PROGRAMMABLE FULL-SCALE
ꢀ SINGLE SUPPLY
ꢀ CASCADABLE OUTPUT
To provide single-supply operation, the internal A/D converter
APPLICATIONS
ꢀ DIRECT PHOTOSENSOR DIGITIZATION
utilizes a differential input, with the positive input tied to VREF
.
When the integration capacitor is reset at the beginning of
each integration cycle, the capacitor charges to VREF. This
charge is removed in proportion to the input current. At the
end of the integration cycle, the remaining voltage is com-
ꢀ CT SCANNER DAS
ꢀ INFRARED PYROMETER
ꢀ PRECISION PROCESS CONTROL
ꢀ LIQUID/GAS CHROMATOGRAPHY
ꢀ BLOOD ANALYSIS
pared to VREF.
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.
Protected by US Patent #5841310
AVDD
AGND
VREF
DVDD DGND
CAP1A
CAP1A
CHANNEL 1
DCLK
IN1
Dual
Switched
Integrator
DVALID
CAP1B
CAP1B
∆Σ
Modulator
DXMIT
DOUT
DIN
Digital
Filter
Digital
Input/Output
CAP2A
CAP2A
CHANNEL 2
RANGE2
RANGE1
RANGE0
IN2
Control
Dual
Switched
Integrator
CAP2B
CAP2B
TEST
CLK
CONV
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
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