Data Sheet

ADA4558

Rev. 0 | Page 9 of 12

THEORY OF OPERATION

The ADA4558 interfaces to a range of Wheatstone resistive

bridge sensors. Figure 1 shows the block diagram of the

ADA4558. The differential signal from the bridge output is

applied to the analog front end (AFE) and then to the infinite

impulse response (IIR) filter. A correction algorithm is applied

in the processor to compensate for sensor nonlinearity and

temperature dependency.

The ADA4558 power section includes the 4 V regulator output

at the VREG pin, which drives the bridge and the external

temperature sensor. The VREG pin also supplies the reference

to the ADC to create a fully ratiometric measurement system.

The AFE consists of an input EMI filter, inverting input switch,

PGA, low-pass filter, mux switch, and 14-bit successive

approximation register (SAR) ADC.

The differential signal from the bridge sensor is applied to the

PGA, which amplifies the input differential signal and applies

sensor offset voltage adjustment.

The internal mux selects the signal from the PGA, internal

temperature sensor, external local temperature (optional), and

other miscellaneous signals, and applies them to the 14-bit on-

chip SAR ADC, which in turn converts the analog inputs into

the digital domain for further processing.

Next, the digital signal is applied to the IIR filter to filter out any

unwanted noise signals, after which time the filtered signal is

applied to the processor.

The ADA4558 and bridge sensor are calibrated over its signal

and temperature range by the customer via the ADA4558 LIN

interface. Correction coefficients are calculated and stored in

EEPROM. During normal operation, these correction coefficients

are applied to the correction algorithm.

The ADA4558 uses a LIN interface to provide linearized bridge

sensor data in customizable frame formats. The ADA4558 also

provides temperature and extensive diagnostics and status

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.