TA0105A Datasheet, PDF (22/29 Pages) Tripath Technology Inc. – STEREO CLASS-T DIGITAL AUDIO AMPLIFIER DRIVER USING DIGITAL POWER PROCESSING (DPPTM ) TECHNOLOGY

Tripath Technology, Inc. - Technical Information
VN12 SUPPLY
VN12 is an additional supply voltage required by the TA0105A. VN12 must be 12 volts more positive
than the nominal VNN. VN12 must track VNN. Generating the VN12 supply requires some care.
The proper way to generate the voltage for VN12 is to use a 12V-postive supply voltage referenced to the
VNN supply. Figure 5 shows the correct way to power the TA0105A:
VPP
VPP
VNN
5V
PGND
12V
V5
AGND
VN12
VNN
Figure 5: Proper Power Supply Connection
One apparent method to generate the VN12 supply voltage is to use a negative IC regulator to drop
PGND down to 12V (relative to VNN). This method will not work since negative regulators only sink
current into the regulator output and will not be capable of sourcing the current required by VN12.
Furthermore, problems will arise since VN12 will not track movements in VNN.
A common approach is to use an additional secondary on the power transformer to generate an isolated,
say 15VAC voltage. This AC voltage is then full bridge rectified and filtered to produce a DC input voltage
for a LM7812 or similar. The “ground” of the LM7812 is then connected to VNN and thus VN12 will be
properly referenced. Please refer to Figure 6.
15VAC
IN _LM7812 OUT
VN12
+
GND
+
AC LINE
INPUT
VPP
+
PGND
+
VNN
Figure 6: Proper VN12 Supply Generation
OUTPUT TRANSISTOR SELECTION
The key parameters to consider when selecting what MOSFET to use with the TA0105A are drain-source
breakdown voltage (BVdss), gate charge (Qg), and on-resistance (R_DS(ON)).
The BVdss rating of the MOSFET needs to be selected to accommodate the voltage swing between
V_SPOS and V_SNEG as well as any voltage peaks caused by voltage ringing due to switching transients. With
a ‘good’ circuit board layout, a BVdss that is 25% higher than the VPP and VNN voltage swing is a
reasonable starting point. The BVdss rating should be verified by measuring the actual voltages
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TA0105A – RW/ Rev. 2.2/05.05