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turn-off of one transistor and the turn-on of the other in order to minimize shoot-through currents. For
applications using the TP2050 please tie BBM0 and BBM1 to 5V for optimal operation.
Input Stage Design
The TC2000 input stage is configured as an inverting amplifier, allowing the system designer flexibility
in setting the input stage gain and frequency response. Figure 1 shows a typical application where
the input stage is a constant gain inverting amplifier. The input stage gain should be set so that the
maximum input signal level will drive the input stage output to 4Vpp.
TC2000
OAOUT1
RF
RI
INV1
V5
CI
INPUT1
-
+
BIASCAP
AGND
V5
+
INV2
-
CI
INPUT2
RF
RI
OAOUT2
AGND
Figure 1: Input Stage
The gain of the input stage, above the low frequency high pass filter point, is that of a simple inverting
amplifier: It should be noted that the input amplifiers are biased at approximately 2.5VDC. Thus, the
polarity of C
I
must be followed as shown in Figure 1 for a standard ground referenced input signal
A
V
INPUT STAGE
=−
R
F
R
I
Input Capacitor Selection
C
I
can be calculated once a value for R
I
has been determined. C
I
and R
I
determine the input low
frequency pole. Typically this pole is set below 10Hz. C
I
is calculated according to:
C
I
=
where:
1
2
π
f
P
R
I
R
I
= Input resistor value in ohms.
f
P
= Input low frequency pole (typically 10Hz or below)
Modulator Feedback Design
The modulator converts the signal from the input stage to the high-voltage output signal. The
optimum gain of the modulator is determined from the maximum allowable feedback level for the
modulator and maximum supply voltage for the power stage. Depending on the maximum supply
voltage, the feedback ratio will need to be adjusted to maximize performance. The values of RFBB
and RFBC (see explanation below) define the gain of the modulator. Once these values are chosen,
based on the maximum supply voltage, the gain of the modulator will be fixed even as the supply
voltage fluctuates due to current draw.
6
TC2000 – KLI/1.1/12-03
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