XR18910 datasheet(12/19 Pages) EXAR

12 / 19 page

12/19

REV1A

Functional Block Diagram

PGA

10-Bit Offset DAC

1.5V

Reference

I2C Serial Digital Interface

LDO Enable

LDO Select ( 3V, 2.65V )

Input 1 +/-

AGND

DGND

Input 2 +/-

Input 8 +/-

VCC

VDD

SDA

SCL

LDO Output

Output

Application Information

The XR18910 sensor interface includes a 8:1 differential

multiplexer (MUX), a programmable gain instrumentation

amplifier, a 10-bit offset correction DAC and an LDO. An

I2C interface controls the many functions and features of the

XR18910. The XR18910 is designed to integrate multiple

bridge sensors with an ADC/MCU or FPGA.

Each bridge sensor connected to the XR18910 has its

own inherent offset that if not calibrated out can decrease

sensitivity and overall performance of the sensor system. The

on-board DAC introduces an offset into the instrumentation

amplifier to calibrate the offset voltage generated by the

sensors. An independent offset can be set for each of the

8 channels. Only the offset voltage of the active channel is

applied to the PGA.

The programmable gain instrumentation amplifier offers 8

selectable gains from 2V/V to 760V/V to amplify the signal

such that it falls within the input range of the ADC.

An integrated LDO provides a regulated voltage to power

the input bridge sensors and is selectable, between 3V and

2.65V. The LDO can be set to turn off when the XR18910 is

in sleep mode to save power.

The XR18910 also provides the ability to monitor the LDO

current. When the XR18910 is in current sense mode, an

internal 2:1 MUX allows a voltage proportional to the LDO

current to be present at the output. Once all channels have

been calibrated, the LDO current can be used to indirectly

monitor any voltage or resistive changes seen by the inputs.

The XR18910 also includes an internal 1.5V reference that

is used by the internal LDO circuitry and used to set the

reference voltage for the programmable gain instrumentation

amplifier.

During sleep mode, the analog components of the XR18910

are powered down for added power savings.

The XR18910 offers many functions, each controlled by the

I2C compatible serial interface:

■

Input Selection

■

Gain Selection

■

Offset Correction

■

LDO Enable/Select

■

Current Sense Mode

■

Sleep Mode (analog power down)

Figure 20. Functional Block Diagram

18910

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