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IRS20954STRPBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P25
Not recommended for new designs. IRS20954SPBF
Please use IRS20957SPBF.
www.irf.com 16
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
Ω=
Ω⋅=
Ω⋅=
k
k
V
V
k
V
V
R
REF
OCSET
8.5
10
1.5
0.3
10
5
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, t
f
)
Not recommended for new designs. IRS20954SPBF
Please use IRS20957SPBF.
www.irf.com 17
HO (or LO)
LO (or HO)
tf
Dead-
time
Effective dead-time
10%
10%
90%
Figure 15: Effective Deadtime
A longer dead time period is required for a MOSFET with a larger gate charge value because of the longer t
f
. A shorter
effective deadtime setting is always beneficial to achieve better linearity in the Class D switching stage. However, the likelihood
of shoot-through current increases with narrower deadtime settings in mass production. Negative values of effective deadtime
may cause excessive heat dissipation in the MOSFETs, potentially leading to serious damage. To calculate the optimal
deadtime in a given application, the fall time tf for both output voltages, HO and LO, in the actual circuit needs to be measured.
In addition, the effective deadtime can also vary with temperature and device parameter variations. Therefore, a minimum
effective deadtime of 10 ns is recommended to avoid shoot-through current over the range of operating temperatures and
supply voltages.
Programming Deadtime
DT pin provides a function setting deadtime. The IRS20954 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 internal reference voltages.
Threshold voltages for each mode are set internally by a resistive voltage divider off V
CC
, negating the need of using a precise
absolute voltage to set the mode. The relationship between the operation mode and the voltage at DT pin is illustrated in the
Fig. 16 below.
.
Vcc 0.57xVcc 0.36xVcc 0.23 xVcc
45nS
35nS
25nS
15nS
V
DT
Dead-time
Figure 16: Deadtime Settings vs. V
DT
Voltage
Not recommended for new designs. IRS20954SPBF
Please use IRS20957SPBF.
www.irf.com 18
Table 1 shows suggested values of resistance for setting the deadtime. Resistors with up to 5% tolerance can be used if these
listed values are followed.
Vcc
COM
DT
>0.5mA
R6
R7
IRS20954
Figure 17: External Resistor
Deadtime
mode
R6 R7 DT/SD
voltage
DT1 <10 kΩ Open (V
cc
)
DT2 5.6 kΩ 4.7 kΩ 0.46(V
cc
)
DT3 8.2 kΩ 3.3 kΩ 0.29(V
cc
)
DT4 Open <10 kΩ kΩ COM
Table 1: Suggested Resistor Values for Deadtime Settings
Power Supply Considerations
Supplying V
DD
V
DD
is designed to be supplied with the internal zener diode clamp. V
DD
supply current I
DD
can be estimated by:
I
DD
= 1.5 mA x 300 x 10
-9
x switching frequency + 0.5 mA + 0.5 mA
(Dynamic power consumption) (Static) (zener bias)
The resistance of R
dd
to feed this I
DD
therefore is:
DD
B
I
VV
Rdd
8.10−
≤
+ [Ω]
In case of 400 kHz average PWM switching frequency, the required I
DD
is 1.18 mA. A condition using 50 V power supply
voltage yields R
dd
=33 kΩ.
Make sure I
DD
is below the maximum zener diode bias current, I
DDZ,
at static state conditions such as a condition with no PWM
input.
mA
Rdd
VV
I
B
DDZ
5.0
8.10
−
−
≥
+
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P25

IRS20954STRPBF

Mfr. #:
Buy IRS20954STRPBF
Manufacturer:
Infineon Technologies
Description:
IC DVR DGTL AUDIO PROT 16-SOIC
Lifecycle:
New from this manufacturer.
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