Pin 6, V S Power Supply. SeekIC only pays the seller after confirming you have received your order. A conservative approach dqtasheet be sure there is at. The protection circuitry monitors the current. Internal charge pump with external bootstrap capability.
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Typically the ceramic capacitor can be eliminated in the presence of the voltage suppressor. With any power device it is important to consider the effects of the substantial surge cur- rents through the device that may occur as a result of shorted loads. The protection circuitry monitors the current through the upper transistors and shuts off the power device as quickly as possible in the event of an overload condition the threshold is set to approximately 10A.
In a typical motor driving application the most common overload faults are caused by shorted motor windings and locked rotors. Under these conditions the inductance of the motor as well as any series inductance in the V CC supply line serves to reduce the magnitude of a current surge to a safe level for the LMD Once the device is shut down, the control cir- cuitry will periodically try to turn the power device back on.
This feature allows the immediate return to normal operation once the fault condition has been removed. While the fault remains however, the device will cycle in and out of thermal shutdown. This can create voltage transients on the V CC supply line and therefore proper supply bypassing tech- niques are required. This condition can generate a surge of current through the power device on the order of 15 Amps and re- quire the die and package to dissipate up to W of power for the short time required for the protection circuitry to shut off the power device.
Proper heat sink design is essential and it is normally necessary to heat sink the V CC supply pin pin 6 with 1 square inch of copper on the PC board. To achieve this an in- ternal charge pump is used to provide the gate drive voltage.
As shown in Figure 4 , an internal capacitor is alternately switched to ground and charged to about 14V, then switched to V S thereby providing a gate drive voltage greater than VS. This switching action is controlled by a continuously running internal kHz oscillator. For higher switching frequencies, the LMD provides for the use of external bootstrap capacitors.
The bootstrap principle is in essence a second charge pump whereby a large value capacitor is used which has enough energy to quickly charge the parasitic gate input capacitance of the power device resulting in much faster rise times. The switch- ing action is accomplished by the power switches them- selves Figure 5. External 10 nF capacitors, connected from the outputs to the bootstrap pins of each high-side switch provide typically less than ns rise times allowing switch- ing frequencies up to kHz.
Each of the four switches in the LMD 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 protect- ing the sourcing power devices is typically only 70 ns with a reverse recovery current of 1A when tested with a full 3A of forward current through the diode.
For the sinking devices the recovery time is typically ns with 4A of reverse cur- rent under the same conditions.
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