9

LT1792

S

APPLICATI

I FOR ATIO

the input of the LT1792. The charge across the transducer

equal the transducer capacitance plus the input capaci-

noninverting mode example, the transducer current is

converted to a change in voltage by the transducer capaci-

tance; this voltage is then buffered by the LT1792 with a

either the transducer impedance or an external resistor.

balance the DC offset caused by the noninverting input

small at room temperature, can create significant errors at

higher temperature, especially with transducer resistances

is used to cancel the phase shift caused by the op amp

Reduced Power Supply Operation

The LT1792 can be operated from

±5V supplies for lower

expense of reduced dynamic range. To illustrate this

benefit, let’s take the following example:

An LT1792CS8 operates at an ambient temperature of

25

°C with ±15V supplies, dissipating 159mW of power

(typical supply current = 5.3mA). The SO-8 package has a

crease of 30.2

°C or a room temperature die operating

temperature of 55.2

°C. At ±5V supplies, the die tempera-

ture increases by only one third of the previous amount or

10.1

°C resulting in a typical die operating temperature of

only 35.1

°C. A 20 degree reduction of die temperature is

achieved at the expense of a 20V reduction in dynamic

range.

To take full advantage of a wide input common mode

range, the LT1792 was designed to eliminate phase rever-

sal. Referring to the photographs shown in Figure 4, the

at

±5V supplies with the input swinging ±5.2V. The output

of the LT1792 clips cleanly and recovers with no phase

reversal. This has the benefit of preventing lock-up in

servo systems and minimizing distortion components.

High Speed Operation

The low noise performance of the LT1792 was achieved

by making the input JFET differential pair large to maxi-

mize the first stage gain. Increasing the JFET geometry

INPUT:

±5.2V Sine Wave

LT1792 Output

1792 F04a

1792 F03b