IRS20954S Datasheet, PDF (16/25 Pages) International Rectifier – Protected Digital Audio Driver

IRS20954S
Low Side Over-current Setting
Designing with the same MOSFET as in high side with R_DS(ON) of 100 mΩ, the OCSET voltage, V_OCSET, to set 30 A
trip level is given by:
V_OCSET = I_TRIP+ x R_DS(ON) = 30 A x 100 mΩ = 3.0 V
Choose R4+R5=10 kΩ for proper loading of VREF pin, thus
R₅
=
V_OCSET
V_REF
⋅10kΩ
= ^3.0V ⋅10kΩ
5.1V
= 5.8kΩ
Where V_REF is the output voltage of VREF pin, 5.1 V typical.
Choose R5 = 5.6 kΩ and R4 = 3.9 kΩ from E-12 series.
In general, R_DS(ON) has a positive temperature coefficient that needs to be considered when the threshold level is being set.
Although this characteristic is preferable from a device protection point of view, these variation needs to be considered as well
as variations of external or internal component values.
Deadtime Generator
The deadtime generator block provides a blanking time between the high-side on and low-side on to avoid a simultaneous on
state causing shoot-through. The IRS20954 has an internal deadtime generation block to reduce the number of external
components in the output stage of a Class D audio amplifier. Selectable deadtime programmed through the DT/SD pin voltage
is an easy and reliable function, which requires only two external resistors. This selectable deadtime way of setting prevents
outside noise from modulating the switching timing, which is critical to the audio performances.
How to Determine Optimal Deadtime
The effective deadtime in an actual application differs from the deadtime specified in this datasheet due to finite switching fall
time, t_f. The deadtime value in this datasheet is defined as the time period from the starting point of turn-off on one side of the
switching stage to the starting point of turn-on on the other side as shown in Fig. 15. The fall time of MOSFET gate voltage
must be subtracted from the deadtime value in the datasheet to determine the effective dead time of a Class D audio amplifier.
(Effective deadtime) = (Deadtime in datasheet) – (fall time, tf)
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