FEATURES
SINGLE-CHIP SOLUTION TO DIRECTLY
MEASURE EIGHT LOW-LEVEL CURRENTS
HIGH PRECISION, TRUE INTEGRATING
FUNCTION
INTEGRAL LINEARITY:
±
0.01% of Reading
±
0.5ppm of FSR
VERY LOW NOISE: 5.2ppm of FSR
LOW POWER: 13.5mW/channel
ADJUSTABLE DATA RATE: Up to 3.125kSPS
PROGRAMMABLE FULL SCALE
DAISY-CHAINABLE SERIAL INTERFACE
Dual
Switched
Integrator
Dual
Switched
Integrator
Σ
Modulator
Digital
Filter
Digital
Input/Output
FORMAT
DCLK
DCLK
DVALID
DOUT
DOUT
DIN
DIN
Control
IN3
IN1
VREF
DVDD
AVDD
DGND
AGND
Dual
Switched
Integrator
Dual
Switched
Integrator
Σ
Modulator
Digital
Filter
IN4
IN2
Dual
Switched
Integrator
Dual
Switched
Integrator
Σ
Modulator
Digital
Filter
IN7
IN5
Dual
Switched
Integrator
Dual
Switched
Integrator
Σ
Modulator
Digital
Filter
IN8
IN6
CLK
CONV
RANGE0
RANGE1
RANGE2
TEST
CLK_4X
HISPD/LOPWR
RESET
APPLICATIONS
CT SCANNER DAS
PHOTODIODE SENSORS
INFRARED PYROMETER
LIQUID/GAS CHROMATOGRAPHY
Protected by US Patent #5841310
DESCRIPTION
The DDC118 is a 20-bit octal channel, current-input
analog-to-digital (A/D) converter. It combines both
current-to-voltage and A/D conversion so that eight
low-level current output devices, such as photodiodes, can
be directly connected to its inputs and digitized.
For each of the eight inputs, the DDC118 provides a
dual-switched integrator front-end. This design allows for
continuous current integration: while one integrator is
being digitized by the onboard A/D converter, the other is
integrating the input current. Adjustable full-scale ranges
from 12pC to 350pC and adjustable integration times from
50
μ
s to 1s allow currents from fAs to
μ
As to be measured
with outstanding precision. Low-level linearity is
±
0.5ppm
of the full-scale range and noise is 5.2ppm of the full-scale
range.
Two modes of operation are provided. In Low-Power
mode, total power dissipation is only 13.5mW per channel
with a maximum data rate of 2.5kSPS. High-Speed mode
supports data rates up to 3.125kSPS with a corresponding
dissipation of 18mW per channel.
The DDC118 has a serial interface designed for
daisy-chaining in multi-device systems. Simply connect
the output of one device to the input of the next to create
the chain. Common clocking feeds all the devices in the
chain so that the digital overhead in a multi-DDC118
system is minimal.
The DDC118 is a single-supply device using a +5V analog
supply and supporting a +2.7V to +5.25V digital supply.
Operating over the industrial temperature range of 40
°
C
to 85
°
C, the DDC118 is offered in a QFN-48 package.
DDC118
SBAS325A JUNE 2004 REVISED JUNE 2005
Octal Current Input 20-Bit
Analog-To-Digital Converter
www.ti.com
Copyright
20022005, Texas Instruments Incorporated
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.
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