International Rectifier IRAUDAMP4, Руководство пользователя

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RD-0617
Functional Description
Class D Operation
Referring to CH1 as an example, the op-amp U1 forms a front-end second-order
integrator with C11, C13 & R25 + R29P. 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 R13 and
R31 + R33) so that the duty varies according to the instantaneous value of the analog
input signal. The IRS20955 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 IRS20955 drives two
IRF6645 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 L1 and C23,
which filters out the Class D switching carrier signal.
Figure 2. Simplified Block Diagram of Class D Amplifier
Power Supplies
The IRAUDAMP4 has all the necessary housekeeping power supplies onboard and only
requires a pair of symmetric power supplies ranging from ±25 V to ±35 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, C31 and C32 on the
motherboard, along with high-frequency bypass-caps C15-C18 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 IRAUDAMP4 Class D amplifier as the power supply rejection ratio (PSRR) of
the IRAUDAMP4 is excellent (Figure 3).
IRF6645
Direct-FET
Feedback
GND
LPF
+B
-B
Σ
IRS20955S
Gate Driver
U1
U1
Daughter-board
Integrator
PWM
Modulator
and Level
Shifter