Tripath Technology, Inc. - Technical Information
I n p ut C ap aci t o r S el ect i o n
CI can be calculated once a value for RI has been determined. CI and RI determine the input low
frequency pole. Typically this pole is set below 10Hz. CI is calculated according to:
1
C
R
I =
2πf
P
R
I
where:
I = Input resistor value in ohms.
P = Input low frequency pole (typically 10Hz or below)
f
Mo d ulato r F eed b ack Desig n
The modulator feedback converts the high-voltage output-switching signal to voltage levels that the
TCA2002 can process. 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 for proper
operation and to maximize performance. The values of RFBA, RFBB and RFBC (see explanation below)
define the gain of the modulator. In addition, the amplifier architecture affects the value of the
feedback resistor values. Once these values are chosen, based on the maximum supply voltage, the
gain of the modulator will be fixed even as the supply voltage changes. Thus, an amplifier based on
TCA2002 has inherent PSRR unlike many other commercially available switching amplifiers.
For the best signal-to-noise ratio and lowest distortion, the maximum differential modulator feedback
voltage should be 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.
Mo d ulato r F eed b ack Desig n
For SPLIT-SUPPLY, SINGLE ENDED operation:
VPP
MOSFETS
FET Driver
TCA2002
HS GATE
LS GATE
Y1
Y1B
HIN
LIN
HS OUT
LS OUT
HB OUT
FBKP1 FBKN1
V5
RFBA
VNN
RFBC
RFBB
V5
RFBA
RFBC
RFBB
Figure 3: Split Supply, Single Ended Circuit (One Channel)
Figure 3 shows the basic split supply, single ended amplifier using a TCA2002. The MOSFET output
stage operates from two power supplies, VPP and VNN, that are equal magnitude, but opposite
polarity (for instance +/-60VDC). One terminal of the load is driven by the half-bridge MOSFET
output stage. The other load terminal is ground referenced. Differential feedback is taken from the
10
TCA2002 – KLi/0.95/04.06
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