Part Details for ADP2300 by Analog Devices Inc

A functional block diagram of the circuit is shown in Figure 1. Complete schematics of each section are included in the CN0190 Design Support Package. This module supplies most of the typical power rails required for digital and analog circuits and also demonstrates an easy way to realize overvoltage, undervoltage, and overcurrent detection and protection. In addition, this module shows how to implement sequencing and power margining control.

The heart of the solution is the AD7768-1, which is a low power, high performance, Σ-Δ ADC, with a Σ-Δ modulator and digital filter for precision conversion of both ac and dc signals. The AD7768-1 offers the user flexibility to configure and optimize for input bandwidth vs. output data rate (ODR) vs. power dissipation.

The AD5668 is a 16-bit, octal, voltage output denseDAC controlled by an SPI interface. It contains an on-chip reference with a 10 ppm/°C maximum drift specification. The on-chip reference is off at power-up, allowing the use of an external reference. The internal reference is enabled via a software write. In This circuit , an external REF192 is used because a low output impedance is required to drive the 2.5 V pseudo ground reference for the AD8638 op amps.

This circuit enhances the slew rate control and dynamic power control features of the AD5755 to create a more complete and robust DAC solution. By implementing a simple step-down dc-to-dc converter using the ADP2300, the circuit can provide higher than normal supply currents that are required when slewing the AD5755 outputs.

The excitation square wave for the conductivity cell is generated by switching the ADG1419 between the +VEXC and −VEXC voltages using the PWM output of the ADuCM360 microcontroller. It is important that the square wave has a precise 50% duty cycle and a very low dc offset. Even small dc offsets can damage the cell over a period of time.