ADR430/ADR431/ADR433/ADR434/ADR435/ADR439

Rev. J | Page 18 of 24

APPLICATIONS INFORMATION

OUTPUT ADJUSTMENT

The ADR43x trim terminal can be used to adjust the output

voltage over a ±0.5% range. This feature allows the system designer

to trim system errors out by setting the reference to a voltage

other than the nominal. This is also helpful if the part is used in

a system at temperature to trim out any error. Adjustment of the

output has negligible effect on the temperature performance of the

device. To avoid degrading temperature coefficients, both the

trimming potentiometer and the two resistors need to be low

temperature coefficient types, preferably <100 ppm/°C.

INPUT

OUTPUT

TRIM

GND

R1

470kΩ

R2

10kΩ (ADR430)

15kΩ (ADR431)

10kΩ

ADR43x

Figure 34. Output Trim Adjustment

REFERENCE FOR CONVERTERS IN OPTICAL

NETWORK CONTROL CIRCUITS

In Figure 35, the high capacity, all optical router network

employs arrays of micromirrors to direct and route optical

signals from fiber to fiber without first converting them to

electrical form, which reduces the communication speed. The

tiny micromechanical mirrors are positioned so that each is

illuminated by a single wavelength that carries unique information

and can be passed to any desired input and output fiber. The

mirrors are tilted by the dual-axis actuators, which are controlled

by precision ADCs and DACs within the system. Due to the

microscopic movement of the mirrors, not only is the precision

of the converters important but the noise associated with these

controlling converters is also extremely critical. Total noise

within the system can be multiplied by the number of converters

employed. Therefore, to maintain the stability of the control

loop for this application, the ADR43x, with its exceptionally low

noise, is necessary.

GND

SOURCE FIBER

GIMBAL + SENSOR

DESTINATION

FIBER

ACTIVATOR

RIGHT

MEMS MIRROR

LASER BEAM

ACTIVATOR

LEFT

AMPL

PREAMP

AMPL

CONTROL

ELECTRONICS

DAC

ADC

DAC

DSP

ADR431

ADR431

ADR431

Figure 35. All Optical Router Network

HIGH VOLTAGE FLOATING CURRENT SOURCE

The circuit in Figure 36 can be used to generate a floating

current source with minimal self heating. This particular

configuration can operate on high supply voltages determined

by the breakdown voltage of the N-channel JFET.

GND

OP90

SST111

VISHAY

2N3904

2.1kΩ

ADR43x

2

6

4

Figure 36. High Voltage Floating Current Source

KELVIN CONNECTION

In many portable instrumentation applications, where printed

circuit board (PCB) cost and area go hand in hand, circuit

interconnects are very often of dimensionally minimum width.

These narrow lines can cause large voltage drops if the voltage

reference is required to provide load currents to various functions.

In fact, circuit interconnects can exhibit a typical line resistance

of 0.45 mΩ/square (for example, 1 oz. Cu). Force and sense

connections, also referred to as Kelvin connections, offer a

convenient method of eliminating the effects of voltage drops

in circuit wires. Load currents flowing through wiring resistance

Kelvin connection of Figure 37 overcomes the problem by

including the wiring resistance within the forcing loop of the

operational amplifier.

Because the amplifier senses the load voltage, the operational

amplifier loop control forces the output to compensate for the

wiring error and to produce the correct voltage at the load.