IR21771S International Rectifier, IR21771S Datasheet - Page 12

• Manufacturer Part Number: IR21771S
• Description: 600V Phase Current Sensing IC for AC Motor Control in a 16-Lead SOIC package
• Manufacturer: International Rectifier

Specifications of IR21771S

• Family Hvic: General Purpose HVICs
• Channels: 1
• Topology: Current Sense
• Application: General Purpose / Motor Control
• Voffset: 600
• Over Current Protection: Yes
• Package: 16 Lead
• Part Status: Active & Preferred

The second stage samples the result of the first
stage at double Sync frequency. This action can be
used to fully remove the odd harmonics from the
input signal.
To perform this cancellation it is necessary a shift of
90 degrees of the SYNC signal with respect to the
triangular carrier edges (SYNC2).
The following timing diagrams show the principle of
odd harmonics cancellation (Figure 15), in which
SYNC2 allows the sampling of stage 1 output
during odd harmonic zero crossings.
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Figure 14: Input filter transfer function (10 kHz PWM)
Figure 13: Simplified block diagram
Odd harmonic cancellation using SYNC2 (i.e. 90
degrees shifted SYNC signal) signal will introduce
Tsync/4 additional propagation delay.
Another way to obtain the same result (odd
harmonics cancellation) can be achieved by
controller computing the average of two consecutive
PO results using SYNC1 (SYNC is in this case
aligned to triangular edges, i.e. 0 degree shift).
This method is suitable for most symmetric (center
aligned) PWM schemes.
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