irs20955 International Rectifier Corp., irs20955 Datasheet - Page 15

• Manufacturer Part Number: irs20955
• Description: Protected Digital Audio Driver
• Manufacturer: International Rectifier Corp.

A longer deadtime period is required for a MOSFET
with a larger gate charge value because of the
longer
setting is beneficial to achieving better linearity in
Class D amplifiers, the likelihood of shoot-through
current increases with narrower deadtime settings.
Negative values of effective deadtime may cause
excessive heat dissipation in the MOSFETs, leading
to
To calculate the optimal deadtime in a given
application, the fall time t
actual circuit need to be taken into account. In
addition, variations in temperature and device
parameters could also affect the effective deadtime
in the actual circuit. Therefore, a minimum effective
deadtime of 10 ns is recommended to avoid shoot-
through current over the range of operating
temperatures and supply voltages.
www.irf.com
t
f
.
Figure 15. Effective Deadtime
. Although a shorter effective deadtime
LO (or HO)
HO (or LO)
potentially
Deadtime Mode
DT1
DT2
DT3
DT4
90%
10%
Table 1 Recommended Resistor Values for Deadtime Selection
Dead-time
datasheet
tf
f
for both HO and LO in the
in
serious
Effective dead - time
R1
Open
<10 kΩ
5.6 kΩ
8.2 kΩ
10%
damage.
R2
Open
4.7 kΩ
3.3 kΩ
<10 kΩ
Programming Deadtime
The IRS20955S selects the deadtime from a range
of preset deadtime values based on the voltage
applied at the DT pin. An internal comparator
translates the DT input to a predetermined dead-
time by comparing the input with internal reference
voltages. These internal reference voltages are set
in the IC through a resistive voltage divider using
V
and the voltage at DT pin is illustrated in the
Figure16 below.
Table 1 suggests pairs of resistor values used in the
voltage divider for selecting deadtime. Resistors
with up to 5% tolerance are acceptable when using
these values.
CC.
The relationship between the operation mode
Figure 17. External Voltage Divider
15nS
25nS
35nS
45nS
Dead- time
Figure 16. Deadtime vs. V
0.23 xVcc
>0.5mA
DT/SD Voltage
V
0.46(V
0.29(V
COM
CC
IRS20955(S)PbF
0.36 xVcc
R1
R2
CC
CC
)
)
0.57 xVcc
Vcc
COM
IRS20955
DT
DT
Vcc
15
V
DT