Datasheet

LMD18201
www.ti.com SNVS092D –APRIL 1998–REVISED APRIL 2013
Figure 11. Transitions in Brake, Direction, or PWM Must be Separated by At Least 1 μsec
SIGNAL TRANSITION REQUIREMENTS
To ensure proper internal logic performance, it is good practice to avoid aligning the falling and rising edges of
input signals. A delay of at least 1 µsec should be incorporated between transitions of the Direction, Brake,
and/or PWM input signals. A conservative approach is be sure there is at least 500ns delay between the end of
the first transition and the beginning of the second transition. See Figure 11.
USING THE THERMAL WARNING FLAG
The THERMAL FLAG output (pin 9) is an open collector transistor. This permits a wired OR connection of
thermal warning flag outputs from multiple LMD18201's, and allows the user to set the logic high level of the
output signal swing to match system requirements. This output typically drives the interrupt input of a system
controller. The interrupt service routine would then be designed to take appropriate steps, such as reducing load
currents or initiating an orderly system shutdown. The maximum voltage compliance on the flag pin is 12V.
SUPPLY BYPASSING
During switching transitions the levels of fast current changes experienced may cause troublesome voltage
transients across system stray inductances.
It is normally necessary to bypass the supply rail with a high quality capacitor(s) connected as close as possible
to the V
S
Power Supply (Pin 6) and POWER GROUND (Pin 7). A 1 μF high-frequency ceramic capacitor is
recommended. Care should be taken to limit the transients on the supply pin below the Absolute Maximum
Rating of the device. When operating the chip at supply voltages above 40V a voltage suppressor (transorb)
such as P6KE62A is recommended from supply to ground. Typically the ceramic capacitor can be eliminated in
the presence of the voltage suppressor. Note that when driving high load currents a greater amount of supply
bypass capacitance (in general at least 100 μF per Amp of load current) is required to absorb the recirculating
currents of the inductive loads.
Copyright © 1998–2013, Texas Instruments Incorporated Submit Documentation Feedback 9
Product Folder Links: LMD18201