TC2001 datasheet(19/34 Pages) TRIPATH

19 / 34 page

Tr i p ath Technol ogy, I n c. - Techni cal In fo rma t io n

TK2150 – Rev. 1.0/12.02

OAOUT1

INV1

AGND

OAOUT2

INV2

AGND

BIASCAP

TC2001

INPUT1

INPUT2

Figure 2: TC2001 Input Stage

Input Capacitor Selection

CIN can be calculated once a value for RIN has been determined. CIN and RIN determine the input

low-frequency pole. Typically this pole is set at 10Hz. CIN is calculated according to:

CIN = 1 / (2π x FP x RIN)

where: RIN = Input resistor value in ohms

FP = Input low frequency pole (typically 10Hz)

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 voltages for the power stage. Depending on the maximum

supply voltage, the feedback ratio will need to be adjusted to maximize performance. The values

of RFBA, 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 with as the supply voltage fluctuates due to current draw.

For the best signal-to-noise ratio and lowest distortion, the maximum modulator feedback voltage

should be approximately 4Vpp. The modulator feedback resistor RFBC should be adjusted so that

the modulator feedback voltage is approximately 4Vpp. This will keep the gain of the modulator

as low as possible and still allow headroom so that the feedback signal does not clip the

modulator feedback stage.

Increasing the value of RFBC will increase the modulator gain.

Sometimes increasing the value of RFBC may be necessary to achieve full power for the amplifier

since the input stage for the TC2001 will clip at approximately 4Vpp. This will ensure that the

input stage doesn’t clip before the output stage.

Figure 3 shows how the feedback from the output of the amplifier is returned to the input of the

modulator. The input to the modulator (FBKOUT1/FBKGND1 for channel 1) can be viewed as

inputs to an inverting differential amplifier. RFBA and RFBB bias the feedback signal to

approximately 2.5V and RFBC scales the large OUT1/OUT2 signal to down to 4Vpp.

TC2001 Datasheet(PDF) 19 Page - Tripath Technology Inc.