LMD18200_13 Datasheet, PDF (12/19 Pages) Texas Instruments – LMD18200 3A, 55V H-Bridge

LMD18200
SNVS091E – MAY 2004 – REVISED FEBRUARY 2011
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Figure 15. Bootstrap Circuitry
INTERNAL PROTECTION DIODES
A major consideration when switching current through inductive loads is protection of the switching power
devices from the large voltage transients that occur. Each of the four switches in the LMD18200 have a built-in
protection diode to clamp transient voltages exceeding the positive supply or ground to a safe diode voltage drop
across the switch.
The reverse recovery characteristics of these diodes, once the transient has subsided, is important. These
diodes must come out of conduction quickly and the power switches must be able to conduct the additional
reverse recovery current of the diodes. The reverse recovery time of the diodes protecting the sourcing power
devices is typically only 70 ns with a reverse recovery current of 1A when tested with a full 6A of forward current
through the diode. For the sinking devices the recovery time is typically 100 ns with 4A of reverse current under
the same conditions.
Typical Applications
FIXED OFF-TIME CONTROL
This circuit controls the current through the motor by applying an average voltage equal to zero to the motor
terminals for a fixed period of time, whenever the current through the motor exceeds the commanded current.
This action causes the motor current to vary slightly about an externally controlled average level. The duration of
the Off-period is adjusted by the resistor and capacitor combination of the LM555. In this circuit the
Sign/Magnitude mode of operation is implemented (see TYPES OF PWM SIGNALS).
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