IRS20955STRPBF International Rectifier, IRS20955STRPBF Datasheet - Page 14

• Manufacturer Part Number: IRS20955STRPBF
• Description: IC DVR DGTL AUDIO PROT 16-SOIC
• Manufacturer: International Rectifier
• Type: MOSFET Driverr

Specifications of IRS20955STRPBF

• Applications: Amplifiers, Receivers
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (3.9mm Width)
• For Use With: IRAUDAMP4 - KIT 2CH 120W HALF BRDG AUDIO AMP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

High-Side Over-Current Setting
Figure 14 demonstrates the typical circuitry used for
high-side current sensing. In the following example,
the over-current protection level is set to trip at 30 A
using a MOSFET with an R
component values of R2 and R3 can be calculated
using the following formula:
Let R2 + R3=10 kΩ.
where V
diode D1 = 0.6 V.
high-side MOSFET when the MOSFET current is 30
A.
Therefore, V
= 3 V
Based on the formulas above, R2 = 6.8 kΩ and R3
= 3.3 kΩ.
Choosing the Right Reverse Blocking Diode
The selection of the appropriate reverse blocking
diode used in place of D1 depends on its voltage
rating and speed. To effectively block bus voltages,
the reverse voltage must be higher than the voltage
difference between +B and -B and the reverse
recovery time must be as fast as the boot strap
charging diode. A diode such as the Philips BAV21
W, a 200 V, 50 ns high speed switching diode, is
more than sufficient.
www.irf.com
V
V
th,OCL
F
DS@ID=30A
= the forward voltage of reverse blocking
DS@ID=30A
= 1.2 V
R
3
= 10
= the voltage drop across the
= I
Figure 14. Programming High-Side Over-Current Threshold
k
D
Ω
x R
⋅
V
Vth
DS(ON)
DS
DS(ON)
Comparator
OC
+
OCH
V
CSH
F
= 30 A x 100 mΩ
of 100 mΩ. The
+
-
1.2V
IRS20955
HO
CSH
VB
HO
VS
LO
R3
R2
Vcc
Deadtime Generator
Deadtime is a blanking period inserted between
high-side turn on and low-side turn on to prevent
shoot through. In the IRS20955S, an internal dead-
time generation block allows the user to select the
optimum deadtime from a range of preset values.
Selecting a preset deadtime through the DT/SD pin
voltage can easily be done through an external
voltage divider. This way of setting deadtime
prevents
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 the switching fall time,
in this datasheet is defined as the time period
between the beginning of turn-off on one side of the
switching stage and the beginning of turn-on on the
other side as shown in Figure 15. The fall time of
MOSFET gate voltage must be subtracted from the
deadtime value in the datasheet to determine the
effective deadtime of a Class D audio amplifier.
(Effective deadtime) = (Deadtime in datasheet) –
R1
D1
Q2
Q1
outside
+B
-B
OUT
IRS20955(S)PbF
noise
from
t
f
.
. The deadtime value
modulating
14
the
t
f
.