Datasheet ADA4558 (Analog Devices) - 9

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Data Sheet ADA4558 THEORY OF OPERATION
The ADA4558 interfaces to a range of Wheatstone resistive The internal mux selects the signal from the PGA, internal bridge sensors. Figure 1 shows the block diagram of the temperature sensor, external local temperature (optional), and ADA4558. The differential signal from the bridge output is other miscellaneous signals, and applies them to the 14-bit on- applied to the analog front end (AFE) and then to the infinite chip SAR ADC, which in turn converts the analog inputs into impulse response (IIR) filter. A correction algorithm is applied the digital domain for further processing. in the processor to compensate for sensor nonlinearity and Next, the digital signal is applied to the IIR filter to filter out any temperature dependency. unwanted noise signals, after which time the filtered signal is The ADA4558 power section includes the 4 V regulator output applied to the processor. at the VREG pin, which drives the bridge and the external The ADA4558 and bridge sensor are calibrated over its signal temperature sensor. The VREG pin also supplies the reference and temperature range by the customer via the ADA4558 LIN to the ADC to create a ful y ratiometric measurement system. interface. Correction coefficients are calculated and stored in The AFE consists of an input EMI filter, inverting input switch, EEPROM. During normal operation, these correction coefficients PGA, low-pass filter, mux switch, and 14-bit successive are applied to the correction algorithm. approximation register (SAR) ADC. The ADA4558 uses a LIN interface to provide linearized bridge The differential signal from the bridge sensor is applied to the sensor data in customizable frame formats. The ADA4558 also PGA, which amplifies the input differential signal and applies provides temperature and extensive diagnostics and status sensor offset voltage adjustment. information. LIN 2.1, LIN 2.0, and LIN 1.3 modes are supported. For more information and register details for the ADA4558, see the ADA4558 Hardware Reference Manual. Rev. 0 | Page 9 of 12 Document Outline FEATURES APPLICATIONS GENERAL DESCRIPTION FUNCTIONAL BLOCK DIAGRAM TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE ESD CAUTION PIN CONFIGURATION AND FUNCTION DESCRIPTIONS TYPICAL PERFORMANCE CHARACTERISTICS THEORY OF OPERATION APPLICATIONS INFORMATION TYPICAL CONNECTION DIAGRAM EMC PERFORMANCE PCB LAYOUT GUIDELINES OUTLINE DIMENSIONS ORDERING GUIDE AUTOMOTIVE PRODUCTS