LTC2358-18 ADC reduces size to save PCB real estate

The latest buffered, 18-bit, octal ADC from Analog Devices, has picoA inputs to reduce the footprint.

Analog Devices, which recently acquired Linear Technology, has developed the LTC2358-18, eight-channel simultaneous sampling successive approximation register (SAR) analogue digital converter (ADC) with integrated picoA input buffers. As board real estate is at a premium, the LTC2358-18 brings “substantial” space and cost savings, says Analog Devices, by eliminating front-end signal conditioning circuitry, normally required to drive unbuffered switched-capacitor ADC inputs. The combined component savings of three amplifiers, six resistors and two capacitors for each channel, equate to a total of 88 components over eight channels, points out Analog Devices, to save bill of material (BoM) cost and board space and to provide over 40 per cent savings in power consumption. PicoA inputs and 128dB common-mode rejection ratio (CMRR) over a 30VP-P common mode range enable the LTC2358-18 to directly connect to a range of sensors without compromising measurement accuracy, says Analog Devices.

While converting eight channels at 200ksample/s/channel throughput, the LTC2358-18 provides added flexibility via independently configurable SoftSpan input ranges. Each channel can be programmed on a conversion-by-conversion basis to accept ±10.24, 0V to 10.24, ±5.12, or 0 to 5.12V unipolar, true bipolar, fully differential or arbitrary input signals. The differential analogue inputs operate over a wide 30V input common mode range, allowing the ADC to directly digitise a variety of signals while simplifying the signal chain design. The input signal flexibility, combined with ±3.5LSB  maximum INL, no missing codes at 18-bit, and 96.4dB signal to noise ration (SNR), make the LTC2358-18 a practical choice for high performance industrial process control, test and measurement, power line monitoring and motor control applications.

The LTC2358-18 features a precision internal reference with 20ppm/degree C maximum temperature co-efficient and an integrated reference buffer capable of accurate one-shot measurements. This also saves space in densely packed circuit boards. Optionally, an external 5.0V reference can be used to expand the analogue input range to ±12.5V. The LTC2358-18  dissipates 219mW when converting eight channels simultaneously at 200ksample/s/channel, and features nap and power-down modes to reduce power dissipation at slower throughputs.

Analog Devices also points out that the LTC2358-18 offers “unmatched” digital flexibility, with pin-selectable SPI CMOS and LVDS serial interfaces. The wide digital output supply range allows the device to communicate with any CMOS logic between 1.8 and 5.0V. In CMOS mode, applications can employ between one and eight lanes of serial output data, enabling the user to optimisse bus width and data throughput. LVDS mode offers low noise, high speed communications over greater distances using differential signalling. Together, these I/O interface options enable the LTC2358-18 to communicate equally well with legacy microcontrollers and modern FPGAs.

The LTC2358-18 is specified over the −40 to +125 degree C temperature range. It is offered in a 48-lead 7.0 x 7.0mm LQFP that is pin-compatible with Analog Devices’ LTC2348-18.


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