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Reverse battery protection Automotive reverse polarity protection
Reverse battery protection
Automotive reverse polarity protection
In the next few slides, we will review the reverse polarity protection in automotive front end power stage. To protect the downstream circuits from negative polarity resulting from accidental reverse connection of battery terminals, a few different methods are used. The simplest method is to use a Schottky diode. When the reverse voltage is applied, the diode becomes open circuit and protects other components. This method is simplest. But because of the diode drop, there is power loss associated during normal operation. Therefore, this method is limited to [? local end. ?]
Other common method is to use a PFET along with some discrete circuits. For [? correct ?] battery connection, the PFET turns on and provides a low resistance path for the current. For reverse voltages, the PFET turns off, thereby protecting downstream circuits. This method is more efficient than a diode. However, PFETs worse characteristics than NFETs and need external circuits, such as zener clamps and resistors to operate properly. Smart diodes combine the superior performance of NFETs and the simplicity of a diode.
This slide compares the solution sizes of the three solutions utilizing Schottky diode, PFET, and smart diode for a [? six amp ?] design. As can be seen here, the diode area is the biggest, followed by the PFET. The smart diode-based solution results in about 50% smaller solution size than the one based on a Schottky diode. This slide shows the thermal performance of the three solutions. For the same load current of six amps, the smaller smart diode solution runs much cooler than the larger Schottky and the PFET-based solutions.
The transient performance of a PFET-based solution and a smart diode plus NFET-based solution are compared on this slide. The yellow wave form is the input voltage. The perfect waveform is the output voltage. And the green waveform represents the load current. The PFET turn off is slower in response to the reverse voltage. As a result of which, there is negative credit flow, which causes the output voltage to dip. The smart diode responds faster to turn off the [? end channel FET ?] And as a result, it prevents the dip in the output voltage.
2017年 4月 17日
In this video we will review the reverse battery protection stage of the automotive frond-end power stage. To protect the downstream circuits from negative polarity resulting from accidental reverse connection of battery terminals different methods are used.