Slew rate control (Suppressing rush current)
When the output is turned on, an inrush current flows to charge the capacitor connected to the load side. If this current is too large, the overcurrent protection circuit may malfunction, making it impossible to start up, or overshooting may occur in the output voltage.
To prevent this, this function limits the inrush current and controls the slew rate at the rise of the output voltage.
The slew rate control function can control the rise of the output voltage with an external capacitor.
The inside of the red frame in the left figure is the external capacitor CdVdT.
By changing this value, the rising slew rate of the output voltage can be adjusted.
The capacitance of the external capacitor CdVdT and the rise time tdV / dT of the output voltage can be expressed by the formula on the upper right.
The graph on the right shows the above relationship.
From this graph, the horizontal axis shows that the larger the capacitance, the slower the rising tdV / dT of the output voltage on the vertical axis. The rush current can also be reduced by slowly rising this output voltage.
In the configuration with discrete parts, it was necessary to change various constants such as gate voltage, current adjustment, gate capacitance value, etc. to change the slew rate, but with the eFuse IC, the slew rate can be adjusted with a single small capacitor.
The figure below is an example of rush current suppression using slew rate control.
The waveform on the left is the rising waveform of the output voltage and current with dV / dT terminal open, and the waveform on the right is the waveform when 1nF is added to dV / dT terminal.
The slew rate can be adjusted by adjusting the CdVdT terminal capacitance.
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