www.irf.com
Page 13 of 46
IRAUDAMP6 REV 1
.0
Functional Descriptions
Class D Operation
Referring to CH1 as an example, the op-amp U6 forms a front-end second-order integrator with
C38, C42 & R50 + R49P. This integrator receives a rectangular feedback waveform from the
Class D switching stage and outputs a quadratic oscillatory waveform as a carrier signal. To
create the modulated PWM signal, the input signal shifts the average value of this quadratic
waveform (through gain relationship between R40,AR154 and R38 + R39) so that the duty varies
according to the instantaneous value of the analog input signal. The IRS20957 input comparator
processes the signal to create the required PWM signal. This PWM signal is internally level-shifted
down to the negative supply rail where this signal is split into two signals, with opposite polarity
and added deadtime, for high-side and low-side MOSFET gate signals, respectively. The
IRS20957 drives two IRF6785 DirectFET MOSFETs in the power stage to provide the amplified
PWM waveform. The amplified analog output is re-created by demodulating the amplified PWM.
This is done by means of the LC low-pass filter (LPF) formed by L4 and C34, which filters out the
Class D switching carrier signal.
Power Supplies
The IRAUDAMP6 has all the necessary housekeeping power supplies onboard and only requires
a pair of symmetric power supplies ranging from ±38 V to ±82 V (+B, GND, -B) for operation. The
internally-generated housekeeping power supplies include a ±5 V supply for analog signal
processing (preamp, etc.), while a +12 V supply (V
CC
), referenced to –B, is included to supply the
Class D gate-driver stage.
For the externally-applied power, a regulated power supply is preferable for performance
measurements, but not always necessary. The bus capacitors, C45 ~ C48 on the motherboard,
along with high-frequency bypass-caps C19 ~ C26 on daughter board, address the high-frequency
ripple current that result from switching action. In designs involving unregulated power supplies,
the designer should place a set of bus capacitors, having enough capacitance to handle the audio-
ripple current, externally. Overall regulation and output voltage ripple for the power supply design
are not critical when using the IRAUDAMP6 Class D amplifier as the power supply rejection ratio
(PSRR) of the IRAUDAMP6 is excellent (Fig 9).
Summary of Contents for IRAUDAMP6
Page 11: ...www irf com Page 11 of 46 IRAUDAMP6 REV 1 0 Fig 7 Channel separation vs frequency...
Page 32: ...www irf com Page 32 of 46 IRAUDAMP6 REV 1 0 Schematic...
Page 33: ...www irf com Page 33 of 46 IRAUDAMP6 REV 1 0...
Page 34: ...www irf com Page 34 of 46 IRAUDAMP6 REV 1 0...
Page 35: ...www irf com Page 35 of 46 IRAUDAMP6 REV 1 0...
Page 36: ...www irf com Page 36 of 46 IRAUDAMP6 REV 1 0 Fig 22 IRAUDAMP6 Schematic...