DRV103UG4 Datasheet, PDF (12/24 Pages) Burr-Brown (TI) – PWM LOW-SIDE DRIVER (1.5A and 3A) for Solenoids, Coils, Valves, Heaters, and Lamps

The internal protection circuitry of the DRV103 was designed
to protect against overload conditions. It was not intended to
replace proper heat sinking. Continuously running the
DRV103 into thermal shutdown will degrade reliability.
HEAT SINKING
Most applications will not require a heat sink to assure that
the maximum operating junction temperature (125°C) is not
exceeded. However, junction temperature should be kept as
low as possible for increased reliability. Junction tempera-
ture can be determined according to the equation:
T_J = T_A + P_Dθ_JA
(1)
where, θ_JA = θ_JC + θ_CH + θ_HA
(2)
T_J = Junction Temperature (°C)
T_A = Ambient Temperature (°C)
P_D = Power Dissipated (W)
θ_JC = Junction-to-Case Thermal Resistance (°C/W)
θ_CH = Case-to-Heat Sink Thermal Resistance (°C/W)
θ_HA = Heat Sink-to-Ambient Thermal Resistance (°C/W)
θ_JA = Junction-to-Air Thermal Resistance (°C/W)
Using a heat sink significantly increases the maximum
allowable power dissipation at a given ambient temperature.
The answer to the question of selecting a heat sink lies in
determining the power dissipated by the DRV103. 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. For further insight on calculating power
dissipation, refer to Application Bulletin SBFA002 at
www.ti.com. Once power dissipation for an application is
known, the proper heat sink can be selected.
Heat Sink Selection Example
A PowerPAD™ SO-8 (H) package is dissipating 2W. The
maximum expected ambient temperature is 35°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 specification
table, 16.7°C/W. θ_CH depends on heat sink size, area, and
material used. A semiconductor’s package type and mount-
ing can also affect θ_CH. A typical θ_CH for a soldered-in-place
PowerPAD™ SO-8 (H) package is 2°C/W. Now we can
solve for θ_HA:
( ) θ _HA=
T_J – T_A
P_D
–
θ_JC + θ_CH
θ
HA ⁼
125°C – 35°C
2W
–
(16.7°C
/
W
+
2°C
/
W)
(4)
θ _HA= 26.3°C / W
To maintain junction temperature below 125°C, the heat
sink selected must have a θ_HA less than 26.3°C/W. In other
words, the heat sink temperature rise above ambient must be
less than 52.6°C (26.3°C/W • 2W).
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.
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.
RFI/ EMI
Any switching system can generate noise and interference
by radiation or conduction. The DRV103 is designed with
controlled slew rate current switching to reduce these ef-
fects. By slowing the rise and fall times of the output to
0.3µs, much lower switching noise is generated.
Radiation from the DRV103-to-load wiring (the “antenna”
effect) can be minimized by using “twisted pair” cable or by
shielding. Good PCB ground planes are recommended for
low noise and good heat dissipation. Refer to Bypassing
section for notes on placement of the flyback diode.
BYPASSING
A 1µF tantalum bypass capacitor is adequate for uniform
duty cycle control when switching loads of less than 0.5
amps. Larger bypass capacitors are required when switching
high current loads. A 22µF tantalum capacitor is recom-
mended for heavy-duty (3A) applications. It may also be
desirable to run the DRV103 and the load on separate power
supplies at high load currents. Near the absolute maximum
supply voltage of 40V, bypassing is especially critical. In the
event of a current overload, the DRV103 current limit
responds in microseconds, dropping the load current to zero.
With inadequate bypass, energy stored in the supply line
inductance can lift the supply sufficiently to exceed voltage
breakdown with catastrophic results.
Place the flyback diode at the DRV103 end when driving
long (inductive) cables to a remotely located load. This
minimizes RFI / EMI and helps protect the output DMOS
transistor from breakdown caused by dI/dt transients. Fast
rectifier diodes such as epitaxial silicon or Schottky types
are recommended as flyback diodes.
12
DRV103
SBVS029A