International Rectifier IRAUDAMP4, Manual

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RD-0617
Selectable Deadtime
The IRS20955 determines its deadtime based on the voltage applied to the DT pin. An
internal comparator translates which pre-determined deadtime is being used by
comparing the DT voltage with internal reference voltages. A resistive voltage divider
from V
CC
sets threshold voltages for each setting, negating the need for a precise
absolute voltage to set the mode. The threshold voltages between deadtime settings are
set internally, based on different ratios of V
CC
as indicated in the diagram below. In order
to avoid drift from the input bias current of the DT pin, a bias current of greater than
0.5 mA is suggested for the external resistor divider circuit. Suggested values of
resistance that are used to set a deadtime are given below. Resistors with up to 5%
tolerance can be used.
Deadtime mode Deadtime R11 R9 DT Voltage
DT1 ~15 ns
<10k
Ω Open V
CC
DT2 ~25 ns
5.6k
Ω
4.7k
Ω 0.46(V
CC
)
DT3 ~35 ns
8.2k Ω 3.3k Ω
0.29(V
CC
)
DT4 ~45 ns Open
<10k Ω
COM
Figure 8. Deadtime Settings vs. V
DT
Voltage
Over-Current Protection (OCP)
In the IRAUDAMP4, the IRS20955 gate driver accomplishes OCP internally, a feature
discussed in greater detail in the “Protection” section.
Offset Null (DC Offset)
The IRAUDAMP4 is designed such that no output-offset nullification is required. DC
offsets are tested to be less than ±5 mV.
Bridged Output
The IRAUDAMP4 is not intended for BTL operation. However, BTL operation can be
achieved by feeding out-of-phase audio input signals to the two input channels. In BTL
operation, minimum load impedance is 8
Ω and rated power is 240 W non-clipping. The
installed clamping diodes D5 – D8 are required for BTL operation, since reactive energy
flowing from one output to the other during clipping can force the output voltage beyond
the voltage supply rails if not clamped.
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