DRV591 Datasheet, PDF (14/16 Pages) Texas Instruments – 3-A HIGH-EFFICIENCY PWM POWER DRIVER

DRV591
SLOS389A – NOVEMBER 2001– REVISED MAY 2002
The over-temperature fault is reported when the junction
temperature exceeds 130°C. The device continues
operating normally until the junction temperature reaches
190°C, at which point the IC is disabled to prevent
permanent damage from occurring. The system’s
controller must reduce the power demanded from the
DRV591 once the over-temperature flag is set, or else the
device switches off when it reaches 190°C. This fault is not
latched; once the junction temperature drops below
130°C, the fault is cleared, and normal operation resumes.
POWER DISSIPATION AND MAXIMUM
AMBIENT TEMPERATURE
Though the DRV591 is much more efficient than traditional
linear solutions, the power drop across the on-resistance
of the output transistors does generate some heat in the
package, which may be calculated as shown in
equation (8):
ǒ Ǔ²
PDISS + IOUT
rDS(on), _total
(8)
For example, at the maximum output current of 3 A through
a total on-resistance of 130 mΩ (at T_J = 25°C), the power
dissipated in the package is 1.17 W.
Calculate the maximum ambient temperature using
equation (9):
ǒ Ǔ _{TA + TJ * θJA PDISS}
(9)
PRINTED-CIRCUIT BOARD (PCB) LAYOUT
CONSIDERATIONS
Since the DRV591 is a high-current switching device, a
few guidelines for the layout of the printed-circuit board
(PCB) must be considered:
1. Grounding. Analog ground (AGND) and power
ground (PGND) must be kept separated, ideally back
to where the power supply physically connects to the
PCB, minimally back to the bulk decoupling capacitor
(10 µF ceramic minimum). Furthermore, the
PowerPAD ground connection should be made to
AGND, not PGND. Ground planes are not
recommended for AGND or PGND, traces should be
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used to route the currents. Wide traces (100 mils)
should be used for PGND while narrow traces (15
mils) should be used for AGND.
2. Power supply decoupling. A small 0.1 µF to 1 µF
ceramic capacitor should be placed as close to each
set of PVDD pins as possible, connecting from PVDD
to PGND. A 0.1 µF to 1 µF ceramic capacitor should
also be placed close to the AVDD pin, connecting from
AVDD to AGND. A bulk decoupling capacitor of at
least 10 µF, preferably ceramic, should be placed
close to the DRV591, from PVDD to PGND. If power
supply lines are long, additional decoupling may be
required.
3. Power and output traces. The power and output
traces should be sized to handle the desired
maximum output current. The output traces should be
kept as short as possible to reduce EMI, i.e., the
output filter should be placed as close to the DRV591
outputs as possible.
4. PowerPAD. The DRV591 in the Quad Flatpack
package uses TI’s PowerPAD technology to enhance
the thermal performance. The PowerPAD is
physically connected to the substrate of the DRV591
silicon, which is connected to AGND. The PowerPAD
ground connection should therefore be kept separate
from PGND as described above. The pad underneath
the AGND pin may be connected underneath the
device to the PowerPAD ground connection for ease
of routing. For additional information on PowerPAD
PCB layout, refer to the PowerPAD Thermally
Enhanced Package application note, TI literature
number SLMA002.
5. Thermal performance. For proper thermal
performance, the PowerPAD must be soldered down
to a thermal land, as described in the PowerPAD
Thermally Enhanced Package application note, TI
literature number SLMA002. In addition, at high
current levels (greater than 2 A) or high ambient
temperatures (greater than 25°C), an internal plane
may be used for heat sinking. The vias under the
PowerPAD should make a solid connection, and the
plane should not be tied to ground except through the
PowerPAD connection, as described above.
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