irs20954s International Rectifier Corp., irs20954s Datasheet - Page 21

• Manufacturer Part Number: irs20954s
• Description: Protected Digital Audio Driver
• Manufacturer: International Rectifier Corp.

Junction Temperature Estimation
The power dissipation in the IRS20954 consists of following dominant items;
www.irf.com
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-
-
1.
The dissipation in floating input section is given by;
2.
The dissipation in low side includes loss from logic circuitry and loss from driving LO, and is given by;
3.
The dissipation in high side includes loss from logic circuitry and loss from driving LO and is given by;
P
|
P
P
MID
LOW
HIGH
V
I
I

QCC
QBS
P
P
P
P
Where
P
P
V
R
For obtaining a value of R
P
Where
P
P
R
R
R
Qg is total gate charge of low side MOSFET.
P
BUS
MID
LOW
HIGH
MID
ZDD
LDD
+BUS
LOW
LDD
LO
HIGH
R
DD
O
g(int)
g
˜
P
˜
P
is external gate resistance.
DD
V
is equivalent output impedance of LO, typically 10 for the IRS20954.

V
P
ZDD
: dissipation in floating input logic and protection
: Dissipation in Floating Input Section
LDD
is dissipation from gate drive stage to LO.
is a resistor feeding V
LDD
BS
: dissipation in low side
CC
is dissipation from internal logic circuitry.
: Dissipation in Low Side
is dissipation from internal logic circuitry.
: dissipation in high side
V
is dissipation from internal zener diode clamping V
: Dissipation in High Side
is internal gate resistance of MOSFET.
is positive bus voltage feeding V
DD





P
§
¨
¨
©
˜
P
§
¨
¨
©
P
V
LDD
V
LO
Vcc
HO
DD
BS
˜
˜
Q
Q
g
g
˜
˜
f
f
SW
SW
˜
˜
R
R
O
DD
DD
O

, refer to Supplying V

from V
R
R
R
g
R
g
O

O

R
R
g
+BUS
g
(int)
(int)
DD
·
¸
¸
¹
.
·
¸
¸
¹
from.
DD
section above.
DD
voltage.
IRS20954S
21