Si8244 SILABS [Silicon Laboratories], Si8244 Datasheet - Page 18

• Manufacturer Part Number: Si8244
• Description: CLASS D AUDIO DRIVER WITH PRECISION DEAD-TIME GENERATOR
• Manufacturer: SILABS [Silicon Laboratories]

Si824x
3.4. Power Supply Connections
Isolation requirements mandate individual supplies for VDDI, VDDA, and VDDB. The decoupling caps for these
supplies must be placed as close to the VDD and GND pins of the Si824x as possible. The optimum values for
these capacitors depend on load current and the distance between the chip and the regulator that powers it. Low
effective series resistance (ESR) capacitors, such as Tantalum, are recommended.
3.5. Power Dissipation Considerations
Proper system design must assure that the Si824x operates within safe thermal limits across the entire load range.
The Si824x total power dissipation is the sum of the power dissipated by bias supply current, internal switching
losses, and power delivered to the load. Equation 1 shows total Si824x power dissipation. In a non-overlapping
system, such as a high-side/low-side driver, n = 1.
The maximum power dissipation allowable for the Si824x is a function of the package thermal resistance, ambient
temperature, and maximum allowable junction temperature, as shown in Equation 2:
Substituting values for P
dissipation of 1.19 W. Maximum allowable load is found by substituting this limit and the appropriate datasheet
values from Table 1 on page 5 into Equation 1 and simplifying. The result is Equation 3 (0.5 A driver) and
Equation 4 (4.0 A driver), both of which assume VDDI = 5 V and VDDA = VDDB = 18 V.
18
P
where:
P
I
I
C
V
V
F is the switching frequency (Hz)
n is the overlap constant (max value = 2)
DDI
QOUT
D
D
DDI
DDO
int
Dmax
is the total Si824x device power dissipation (W)
=
is the internal parasitic capacitance (75 pF for the 0.5 A driver and 370 pF for the 4.0 A driver)
is the input-side maximum bias current (3 mA)
is the input-side VDD supply voltage (4.5 to 5.5 V)
V
is the driver-side supply voltage (10 to 24 V)
P
where:
P
T
T
ja = Si824x junction-to-air thermal resistance (105 °C/W)
F = Si824x switching frequency (Hz)
is the driver die maximum bias current (2.5 mA)
DDI
Dmax
jmax
A
Dmax
T
= Ambient temperature (°C)
jmax
I
DDI
= Si824x maximum junction temperature (150 °C)

= Maximum Si824x power dissipation (W)
, T
T
---------------------------
+
jmax
2 V
A

ja
, and 
C
C
L(MAX)
L(MAX)
DDO
–
T
A
I
QOUT
ja
=
=
Equation 1.
Equation 2.
Equation 3.
Equation 4.
into Equation 2 results in a maximum allowable total power
1.4 10
------------------------- - 7.5
1.4 10
------------------------- - 3.7
Rev. 0.2
+
C


F
F
int
V
–
–
3
3
DDO
–
–
2
F



+
10
10
2n C
–
–
11
10

L
V
DDO
2
F
