User guide
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V 1.0.1
2021-01-27
REF-AIRCON-C302A-IM564 user guide
Air conditioner application reference design kits
System and functional description
Figure 19 shows the external amplifier gain circuit in the REF-AIRCON-C302A-IM564 reference design, which is a
typical differential amplifier, with input LPF and operational bias. C24, R43, R52, R58, R59 build the input
differential mode LPF, which can damp part of the PWM switching noise. The default low-pass filter time
constant is 2*RC = 2*(R43//R58)*C24 = 239 ns, which corresponds to DC bus current ring time.
The typical setup time is 0.1 ~ 0.5 µs, depending on the PCB layout, DC bus decouple capacitors and the PFC
MOS gate
driver configuration.
Figure 19
PFC current feedback with external op-amp
For better CMR ability, a balanced differential amplifier is highly recommended, which means R73 is equal to
the value of R5 & R60 in parallel.
The divider of R5 & R60 provides operational bias for the amplifier, which affects the maximum motoring
current and regeneration current range. With the default configuration of REF-AIRCON-C302A-IM564, R60=16 k
& R5=240 k, the op-amp operational bias is 5000 mV * 16 / (16+240) = 312 mV, which means:
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Op-amp outputs 312 mV at zero PFC current (PFC stopped)
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If 1X ADC internal gain is selected, 5000 mV range for PFC current sensing (5000 mV – 312 mV = 4688 mV).
And 4688 mV/op-amp gain/RS1 is the maximum allowable PFC current. “PFC Average Inductor Current
Limit Amps * 1.414” should be below this maximum allowable range with at least 10% margin, which is
related to input parameters in MCEWizard.
