AD598

REV. A

–9–

Figure 15. Gain and Phase Characteristics vs. Frequency

(0 kHz–10 kHz)

1000

100

10

1

0.1

0.01

0.1

1

10

C2, C3, C4; C2 = C3 = C4 –

µF

2.5kHz, C

2.5kHz, C

2.5kHz, C

Figure 16. Output Voltage Ripple vs. Filter Capacitance

1000

100

10

1

0.1

0.001

0.01

0.1

110

C2, C3, C4; C2 = C3 = C4 –

µF

Figure 17. Output Voltage Ripple vs. Filter Capacitance

Determining LVDT Sensitivity

LVDT sensitivity can be determined by measuring the LVDT

secondary voltages as a function of primary drive and core posi-

tion, and performing a simple computation.

Energize the LVDT at its recommended primary drive level,

Sensitivity

=

From Figure 18,

Sensitivity

=

1.71 – 0.99

3

× 100 mils =

2.4 mV/V/mil

d = –100 mils

d = 0

A

V

1.71V rms

0.99V rms

100 mils

+

d =

Figure 18. LVDT Secondary Voltage vs. Core Displacement

Thermal Shutdown and Loading Considerations

The AD598 is protected by a thermal overload circuit. If the die

temperature reaches 165

°C, the sine wave excitation amplitude

gradually reduces, thereby lowering the internal power dissipa-

tion and temperature.

Due to the ratiometric operation of the decoder circuit, only

small errors result from the reduction of the excitation ampli-

tude. Under these conditions the signal-processing section of

the AD598 continues to meet its output specifications.

The thermal load depends upon the voltage and current deliv-

ered to the load as well as the power supply potentials. An

LVDT Primary will present an inductive load to the sine wave

excitation. The phase angle between the excitation voltage and

current must also be considered, further complicating thermal

calculations.