DRV8412 Datasheet, PDF (18/28 Pages) Texas Instruments – Dual Full Bridge PWM Motor Driver

DRV8412
DRV8422
DRV8432
SLES242A – DECEMBER 2009 – REVISED DECEMBER 2009
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APPLICATION INFORMATION
SYSTEM DESIGN RECOMMENDATIONS
Voltage of Decoupling Capacitor
The voltage of the decoupling capacitors should be selected in accordance with good design practices.
Temperature, ripple current, and voltage overshoot must be considered. The high frequency decoupling capacitor
should use ceramic capacitor with X5R or better rating. For a 50-V application, a minimum voltage rating of 63 V
is recommended.
VREG Pin
The VREG pin is used for internal logic and not recommended to be used as a voltage source for external
circuitry.
VDD Pin
The transient current in VDD pin could be significantly higher than average current through that pin. A low
resistive path to GVDD should be used. A 22-µF to 47-µF capacitor should be placed on VDD pin beside the
100-nF to 1-µF decoupling capacitor to provide a constant voltage during transient.
OTW Pin
OTW reporting indicates the device approaching high junction temperature. This signal can be used with MCU to
decrease system power when OTW is low in order to prevent OT shut down at a higher temperature.
Mode Select Pin
Mode select pins (M1, M2, and M3) should be connected to either VREG (for logic high) or AGND for logic low. It
is not recommended to connect mode pins to board ground if 1-Ω resistor is used between AGND and GND.
Output Inductor Selection
For normal operation, inductance in motor (assume larger than 10 µH) is sufficient to provide low di/dt output
(e.g. for EMI) and proper protection during overload condition (CBC current limiting feature). So no additional
output inductors are needed during normal operation.
However during a short condition, the motor (or other load) is shorted, so the load inductance is not present in
the system anymore; the current in the device can reach such a high level that may exceed the abs max current
rating due to extremely low impendence in the short circuit path and high di/dt before oc detection circuit kickes
in. So a ferrite bead or inductor is recommended to utilize the short circuit protection feature in DRV8412/22/32.
With an external inductance or ferrite bead, the current will rise at a much slower rate and reach a lower current
level before oc protection starts. The device will then either operate CBC current limit or OC shut down
automatically (when current is well above the current limit threshold) to protect the system.
For a system that has limited space, a power ferrite bead can be used instead of an inductor. The current rating
of ferrite bead has to be higher than the RMS current of the system at normal operation. A ferrite bead designed
for very high frequency is NOT recommended. A minimum impedance of 10 Ω or higher is recommended at 10
MHz or lower frequency to effectively limit the current rising rate during short circuit condition.
The TDK MPZ2012S300A and MPZ2012S101A (with size of 0805 inch type) have been tested in our system to
meet a short circuit condition in the DRV8412. But other ferrite beads that have similar frequency characteristics
can be used as well.
For higher power applications, such as in the DRV8422 and DRV8432, there might be limited options to select
suitable ferrite bead with high current rating. If an adequate ferrite bead cannot be found, an inductor can be
used.
The inductance can be calculated as:
Loc
_ min
=
PVDD ×Toc _ delay
Ipeak - Iave
(1)
Where Toc_delay = 250 nS, Ipeak = 15 A (below abs max rating).
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