Electronic Design

Differentiation And The Industrial Market

Industrial applications, which include arenas as varied as factory automation and automotive design, represent around 30% of the market for most ADC makers. Not surprisingly, ADC manufacturers are aggressively going after this market.

Linear’s 1.5-Msample LTC2351-14 is a 14-bit ADC with an 83-dB CMRR and serial output for multiphase power measurement, multiphase motor control, data-acquisition systems, and uninterrupted power supplies. It simultaneously samples up to six differential inputs, with separate sample-and-hold amplifiers feeding a common multiplexer. (With six different inputs being sampled, the sample rate for each is 250 ksamples/s.)

Low power consumption is a key spec. In normal operation, typical dissipation is 16.5 mW at 3.3 V. A “nap” mode, in which the internal reference remains active, reduces dissipation to 4.5 mW. In “sleep” mode, dissipation is 12 mW. The chip comes in a 32-pin, 5- by 5-mm quad flat no-lead (QFN) package. Prices start at $6.95.

A related single differential-input, low-power, 14-bit chip from Linear, the LTC2356-14, kicks up the serial-output data rate to 3.5 Msamples/s while drawing 18 mW at 3.3 V. Power dissipation is 4 mW in nap mode and 13 mW in sleep mode. Performance specs include 72.3-dB SINAD, 82-dB SFDR at 1.4 MHz, and a 260-dB CMRR while measuring 61.25 V bipolar inputs differentially. It comes in a 10-pin mini small-outline package (MSOP). Pricing begins at $7.95.

The LTC2351 and LTC2356 use a SAR architecture. On the delta-sigma side, Linear recently introduced the LTC2499. This 24-bit, 16-channel ADC incorporates the company’s “Easy Drive” front-end design, which enables high-impedance input measurements without the need for a buffer. Actually, that’s eight differential channels or 16 single-ended channels, or some combination thereof.

On each sample period, the ADC converts either a signal from its multiplexer or the output of an internal temperature sensor and outputs the results on a serial bus. Each time a new channel is selected, the LTC2499’s digital filter settles in a single cycle. Using the internal oscillator, conversions occur at rates of 15 or 7.5 Hz, while the filtering can be configured to reject 50-, 60-, or simultaneous 50/60-Hz line frequencies. Pricing begins at $3.45.

When it comes to product differentiation, these parts combine a progressive improvement in specs from year to year along with special features such as the balanced input-current front end and the fast-settling digital filter. Another such feature is software-programmable input ranges, which Linear calls “SoftScan.” The latest implementation of SoftScan is the LTC1859, a 16-bit, eight-channel, 100-ksample/s ADC.

The chip’s input ranges are programmable to accept 0- to 5-V, 0- to 10-V, 65-V, and 610-V inputs, with the objective of allowing a single-board design to accommodate multiple industrial applications. All channels are fault-protected to ±25 V. An overvoltage fault up to ±25 V on any of the unused channels will not corrupt the accuracy of the selected channel. Like the other Linear parts described above, it has nap and sleep modes for saving power. Pricing begins at $17.95.

Demonstrating a similar sort of differentiation, Maxim Integrated Products’ most recent ADC family of independently programmable, multichannel 16/14-bit converters operate from a single 5-V supply, but accept a range of higher-voltage analog inputs. The differentiation lies in the way that the MAX1300 16-bit, eight- and four-channel ADC family has integrated software. It enables each input channel to be programmed with seven different input ranges for single-ended inputs and three different input ranges for differential inputs.

The programmable analog input-voltage ranges are 624 V, 612 V, 66 V, 63 V, 0 to +12 V, 612 to 0 V, 0 to +6 V, and 26 to 0 V. Each input is protected from transients up to 616.5 V. The ability to digitize inputs up to 12 V, rather than being limited to 10 V, can be important in detecting sensor overvoltage conditions. Traditionally, ADCs above 10 V have simply continued to indicate a full-scale reading. The extra resolution permits circuit designers to implement diagnostics. Prices start at $17.95.

ADI also introduced its own contenders in the industrial arena during the last six months. These ADCs include the 18-bit, 1-Msample/s AD7982; the dual 12-bit, 5-Msample/s, simultaneous sampling AD7356 SAR; and the 24-bit, oversampling, 125-ksample/s AD7766.

Much of today’s differentiation in the industrial market is about power and footprint, especially when the chips are intended for portable medical applications. The AD7982 consumes 7.5 mW, which is 95% less power than the closest competing 18-bit ADC in its class. Its 10-pin QFN package is 80% smaller than any other 18-bit ADC capable of a 1-Msample/s clock rate. Pricing starts at $23.

At 5 Msamples/s, the AD7356 lets circuit designers simultaneously sample two ADC cores. This delivers a 12-bit result with no latency, which is an advantage for optical encoders used in high-speed industrial motor controls and automobile cruise controls. It consumes 35 mW. Pricing starts at $7.89.

With its 108-dB dynamic range at 125 kHz, the 24-bit AD7766 can target applications like echo-location, data acquisition, and industrial vibration analysis, where small or faint signals must be distinguished in the presence of larger signals. Its 1.8-mV/8C offset drift reduces the need to recalibrate the device due to temperature fluctuations. Pricing starts at $5.95.

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