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