Datasheet

19/25
L6229
4.1 OUTPUT CURRENT CAPABILITY AND IC POWER DISSIPATION
In Figure 25 is shown the approximate relation between the output current and the IC power dissipation using
PWM current control.
For a given output current the power dissipated by the IC can be easily evaluated, in order to establish which
package should be used and how large must be the on-board copper dissipating area to guarantee a safe op-
erating junction temperature (125°C maximum).
Figure 25. IC Power Dissipation versus Output Power.
4.2 THERMAL MANAGEMENT
In most applications the power dissipation in the IC is the main factor that sets the maximum current that can
be delivered by the device in a safe operating condition. Selecting the appropriate package and heatsinking con-
figuration for the application is required to maintain the IC within the allowed operating temperature range for
the application. Figures 26, 27 and 28 show the Junction-to-Ambient Thermal Resistance values for the
PowerSO36, PowerDIP24 and SO24 packages.
For instance, using a PowerSO package with copper slug soldered on a 1.5mm copper thickness FR4 board
with 6cm
2
dissipating footprint (copper thickness of 35 µ m), the R
th(j-amb)
is about 35°C/W. Figure 29 shows
mounting methods for this package. Using a multi-layer board with vias to a ground plane, thermal impedance
can be reduced down to 15°C/W.
Figure 26. PowerSO36 Junction-Ambient thermal resistance versus on-board copper area.
No PWM
f
SW
= 30 kHz (slow decay)
Test Conditions:
Supply Voltage = 24 V
0 0.25 0.5 0.75 1 1.25 1.5
0
2
4
6
8
10
P
I
OUT
[A]
D
[W]
I
OUT
I
1
I
3
I
2
I
OUT
I
OUT
13
18
23
28
33
38
43
12345678910111213
Without Ground La
y
er
With Ground La
y
er
With Ground La
y
er+16 via
Holes
sq. cm
ºC / W
On-Board Copper Area