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SLOS390A – NOVEMBER 2001– REVISED MAY 2002
and normal operation resumes. During the under-voltage
condition, the outputs are high-impedance to prevent
PowerPAD ground connection should be made to
AGND, not PGND. Ground planes are not
recommended for AGND or PGND. Wide traces (100
mils) should be used for PGND while narrow traces
(15 mils) should be used for AGND.
over-dissipation due to increased r
.
DS(on)
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
DRV592 once the over-temperature flag is set, or else the
device switches off when it reaches 190°C. This flag is not
latched, once the junction temperature drops below
130°C, the fault is cleared, and normal operation resumes.
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 DRV592, from PVDD to PGND.
POWER DISSIPATION AND MAXIMUM
AMBIENT TEMPERATURE
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 as possible to
the DRV592 outputs.
Though the DRV592 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 (7):
4. PowerPAD.
The DRV592 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 DRV592
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.
+ ǒIOUTǓ2
(7)
P
r
DISS
DS(on), total
For example, at the maximum output current of 3 A through
a total on-resistance of 130 mΩ (at T = 25°C), the power
J
dissipated in the package is 1.17 W.
The maximum ambient temperature may be calculated
using equation (8):
(8)
ǒθ
JA
DISSǓ
T
+ T
*
P
A
J
PRINTED-CIRCUIT BOARD (PCB) LAYOUT
CONSIDERATIONS
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.
Since the DRV592 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
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