LT1793I Ver la hoja de datos (PDF) - Linear Technology
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LT1793I Datasheet PDF : 12 Pages
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LT1793
APPLICATI S I FOR ATIO
resulting in a change in voltage dV, which is equal to dQ/CF.
The gain therefore is CF/CS. For unity-gain, the CF should
equal the transducer capacitance plus the input capaci-
tance of the LT1793 and RF should equal RS.
In the noninverting mode example, the transducer current
is converted to a change in voltage by the transducer
capacitance, CS. This voltage is then buffered by the
LT1793 with a gain of 1 + R1/R2. A DC path is provided by
RS, which is either the transducer impedance or an exter-
nal resistor. Since RS is usually several orders of magni-
tude greater than the parallel combination of R1 and R2, RB
is added to balance the DC offset caused by the noninvert-
ing input bias current and RS. The input bias currents,
although small at room temperature, can create significant
errors at higher temperature, especially with transducer
resistances of up to 1000M or more. The optimum value
for RB is determined by equating the thermal noise (4kTRS)
to the current noise (2qIB) times RS2. Solving for RS
results in RB = RS = 2VT/IB (VT = 26mV at 25°C). A parallel
capacitor CB, is used to cancel the phase shift caused by
the op amp input capacitance and RB.
Reduced Power Supply Operation
To take full advantage of a wide input common mode range,
the LT1793 was designed to eliminate phase reversal.
Referring to the photographs in Figure 5, the LT1793 is
shown operating in the follower mode (AV = 1) at ±5V
supplies with the input swinging ±5.2V. The output of the
LT1793 clips cleanly and recovers with no phase reversal.
This has the benefit of preventing lockup in servo systems
and minimizing distortion components.
Input: ±5.2V Sine Wave
LT1793 Output
LT1793 F05a
Figure 5. Voltage Follower with Input Exceeding the Common Mode Range (VS = ±5V)
LT1793 F05b
9
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