1 Features
1• Single-Chip Solution to Directly Measure 256 Low-
Level Currents Simultaneously
• User Adjustable Full-Scale Range
• Adjustable Speed with Integration Times as Low
as 58.8 μs (17 KSPS per channel) with 24 bit
Resolution
• Power Dissipation as Low as 1.7mW/channel
• Integral Linearity: ±0.025% of Reading ±1 ppm of
Full Scale Reading (all channels active)
• Low Noise
• 24 bit ADC
• No Charge Loss and Simultaneous Sampling
• On-board Temperature Sensor
• In-Package Bypass Capacitors and Reference
Buffer to Reduce PCB Area and Design
Complexity
• Serial LVDS and CMOS Output Interface Option

2 Applications
• CT Scanner Data Acquisition System
• Photodiode Sensors
• X-ray Detection Systems
• Optical Fiber Power Monitoring
• Mutichannel Current/Voltage Instrumentation

3 Description
The DDC2256A is a 24-bit, 256-channel, currentinput
analog-to-digital (A/D) converter. It combines
both current-to-voltage integration and A/D
conversion so that 256 individual low-level current
output devices, such as photodiodes, can be directly
connected to its inputs and digitized in parallel
(simultaneously).
For each of the inputs, the DDC2256A has one low
noise/low power integrator designed to capture all the
charge from the sensor. The integration time is
adjustable from 58.8μs to 100 ms, allowing currents
from fA to uA to be continuously measured with
outstanding precision. The outputs of the integrators
are digitized by sixteen 24-bit low power ADCs and
all the resulting data is output over a single LVDS
serial interface pair designed to minimize noise
coupling in environments with high channel count.
The DDC2256A operates from ±2.5-V analog supply,
1.8-V analog supply (AVDD_18) and 1.8-V digital
supply (DVDD). The device is specified from 0°C to
70°C operating temperature and available in a 14 x
16 mm2 323-ball 0.8 mm-pitch BGA. Finally, the on
board reference buffer and bypass capacitors help
minimize the external component requirements and
further reduce board space.
To request a full data sheet or other design
resources: request DDC2256A