DRV102_15 Datasheet, PDF (14/27 Pages) Texas Instruments – PWM SOLENOID/VALVE DRIVER

The difficulty in selecting the heat sink required lies in
determining the power dissipated by the DRV102. For dc
output into a purely resistive load, power dissipation is simply
the load current times the voltage developed across the
conducting output transistor times the duty cycle. Other loads
are not as simple. Once power dissipation for an application
is known, the proper heat sink can be selected.
Heat Sink Selection Example
A TO-220 package’s maximum dissipation is 2 Watts. The
maximum expected ambient temperature is 80°C. Find the
proper heat sink to keep the junction temperature below
125°C.
Combining Equations 1 and 2 gives:
T_J = T_A + P_D(θ_JC + θ_CH + θ_HA)
(3)
T_J, T_A, and P_D are given. θ_JC is provided in the Specifica-
tions table, 3°C/W. θ_CH can be obtained from the heat sink
manufacturer. Its value depends on heat sink size, area, and
material used. Semiconductor package type, mounting screw
torque, insulating material used (if any), and thermal
joint compound used (if any) also affect θ_CH. A typical θ_CH
for a TO-220 mounted package is 1°C/W. Now we can solve
for θ_HA:
( ) θ_HA
=
T_J – T_A
P_D
–
θ_JC + θ_CH
(4)
θ _HA
=
125°C – 80°C
2W
–
(3°C/ W
+ 1°C/ W)
= 18.5°C/ W
To maintain junction temperature below 125°C, the heat
sink selected must have a θ_HA less than 18.5°C/W. In other
words, the heat sink temperature rise above ambient must be
less than 37°C (18.5°C/W • 2W). For example, at 2 Watts
Thermalloy model number 6030B has a heat sink
temperature rise of about 33°C above ambient, which is
below the 37°C required in this example. Figure 13 shows
power dissipation versus ambient temperature for a TO-220
package with a 6030B heat sink.
Another variable to consider is natural convection versus
forced convection air flow. Forced-air cooling by a small fan
can lower θ_CA (θ_CH + θ_HA) dramatically. Heat sink manufac-
turers provide thermal data for both of these cases. For
additional information on determining heat sink require-
ments, consult Application Bulletin AB-038.
As mentioned earlier, once a heat sink has been selected, the
complete design should be tested under worst-case load and
signal conditions to ensure proper thermal protection.
14
DRV102
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