Texas Instruments TPA3003D2 - Manual (Page 15)

TPA3003D2
SLOS406A − FEBRUARY 2003 − REVISED MARCH 2003
15
www.ti.com
APPLICATION INFORMATION
class-D operation
This section focuses on the class-D operation of the TPA3003D2.
traditional class-D modulation scheme
The traditional class-D modulation scheme, which is used in the TPA032D0x family, has a differential output
where each output is 180 degrees out of phase and changes from ground to the supply voltage, V
CC
. Therefore,
the differential prefiltered output varies between positive and negative V
CC
, where filtered 50% duty cycle yields
0 V across the load. The traditional class-D modulation scheme with voltage and current waveforms is shown
in Figure 22. Note that even at an average of 0 V across the load (50% duty cycle), the current to the load is
high, causing high loss, thus causing a high supply current.
0 V
−12 V
+12 V
Current
OUTP
Differential Voltage
Across Load
OUTN
Figure 22. Traditional Class-D Modulation Scheme’s Output Voltage and
Current Waveforms Into an Inductive Load With No Input
TPA3003D2 modulation scheme
The TPA3003D2 uses a modulation scheme that still has each output switching from 0 to the supply voltage.
However, OUTP and OUTN are now in phase with each other with no input. The duty cycle of OUTP is greater
than 50% and OUTN is less than 50% for positive output voltages. The duty cycle of OUTP is less than 50%
and OUTN is greater than 50% for negative output voltages. The voltage across the load sits at 0 V throughout
most of the switching period, greatly reducing the switching current, which reduces any I
2 R losses in the load.