Electronica: ±25V 8-channel analogue front end ICs for factory automation

Both have inputs that can measure ±25V, with the NAFE71388 being nominally ‘high speed’ and the NAFE11388 ‘low power’.

They both have the same block diagram, and connect to a host over a 32MHz SPI bus. CRC error detection is included, and there are ten GPIOs.

The eight single-ended inputs can be configured as four differential pairs, and multiplexer, programmable gain amplifier, voltage reference and 24bit ΔΣ ADC are built in.

Specs, particularly the power consumption, are similar:

• NAFE71388
  15 to 576k sample/s
  17bit ENOB at 144ksample/s
  135mW typical quiescent consumption
• NAFE11388
  7.5 to 288k sample/s
  17bit ENOB at 72ksample/s
  125mW typical quiescent consumption

Claimed accuracy is 0.005% of full-scale at room temperature after user calibration, and 0.1% over -25 to 105°C (operation is over -40 to +125°C). A ±3°C temperature sensor is included, as is a 0.2% (room temp) internal oscillator and simultaneous 50 Hz/60 Hz line rejection.

With a 2.5kΩ resistor in series, the analogue inputs can withstand + or – 36V for an hour, and even more with respect to some power rails – see page 80 of the data sheets for more detail here.

Three power rails are needed: 3.3V for the logic, and ±7 to ±24V for the analogue sections. The amplifier can be programmed to have gains of 0.2, 0.4, and 0.8V/V, providing differential full ranges of ±25V to ±6.25V.

“In general, all of the high-voltage input characteristics are specified to the linear – nominal – input ranges for all of the channel gain settings, which is 80 % of the full input range”, said NXP. “In addition to the differential signals at the programmable gain amplifier output, one auxiliary differential input and four low-voltage diagnostic signals – the power supplies and an independent coarse voltage reference – are also multiplexed to ADC.”

Protections include 8kV HBM ESD and IEC61000-4-5 2 kV surge.

The temperature sensor is used to trigger an over-temperature warning at 145°C and auto-shutdown at 165°C, and there is a user-programmable temperature alarm.

Data sheets:
NAFE71388
NAFE11388