The LTC2508 32-bit A/D from Linear Technology offers super accuracy, high speed

By Jim Harrison

Many contemporary applications — including data acquisition, industrial control, and medical diagnostics — require linear measurements with both accuracy and speed. The LTC2508-32 provides a unique combination of 14-bit resolution at a speed of 1 Ms/s and 32-bit resolution at 61 s/s to 3.9 ks/s. The IC simultaneously provides two output codes: a 32-bit digitally filtered high-precision low-noise code and a 22-bit no-latency composite code.

The 32-bit A/D yields integral linearity error performance of ±0.5 ppm typical, ±3.5 ppm maximum, and uses a configurable digital filter with a low noise output. It is specified with a zero-scale error of ±13 ppm and a full-scale error of ±100 ppm. The configurable digital filter reduces measurement noise by low-pass filtering and down-sampling the stream of data from the SAR A/D. This converter’s dynamic range is 145 dB with a down-sampling factor of 16384 and 131 dB with a DF of 256. Total harmonic distortion is typically −118 dB.

The fast side output is in the form of a 14-bit differential +8-bit common-mode word output at 1 Ms/s with no latency. It has an integral linearity error of ±0.1 LSB differential and ±0.1 LSB common mode. The common-mode measurement is useful in many sensor interfaces to detect abnormal conditions.

The chip operates from a 2.5-V supply, has guaranteed operation to 85°C (LTC2508I), and takes only 24 mW at 1 Ms/s. It comes in a 7 × 4 plastic DFN24 package and requires an external 2.5 to 5-V reference. The device has a CMRR of 128 db. Pricing for the chip starts at $8.95 ea/1,000.