LMD18200

SNVS091E – MAY 2004 – REVISED FEBRUARY 2011

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Figure 13. Transitions in Brake, Direction, or PWM Must Be Separated By At Least 1 µsec

USING THE CURRENT SENSE OUTPUT

The CURRENT SENSE output (pin 8) has a sensitivity of 377

μA per ampere of output current. For optimal

accuracy and linearity of this signal, the value of voltage generating resistor between pin 8 and ground should be

chosen to limit the maximum voltage developed at pin 8 to 5V, or less. The maximum voltage compliance is 12V.

It should be noted that the recirculating currents (free wheeling currents) are ignored by the current sense

circuitry. Therefore, only the currents in the upper sourcing outputs are sensed.

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 LMD18200'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 inductance.

It is normally necessary to bypass the supply rail with a high quality capacitor(s) connected as close as possible

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.

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