1.2.2. External Circuits
When the power_dwn signal is low (pwr_dwn_inv is high), the voltage regulator (which has an active low shutdown control) is switched on and the capacitor C discharges. Whenever the device wants to switch off, it makes the power_dwn signal high (pwr_dwn_inv is low). This switches off the voltage regulator, cutting off the power to the device.
When all the I/O pins of the device are tri-stated, the capacitor starts charging. It charges until the voltage across the device remains less than the threshold potential of the regulator’s shutdown control (enhanced by diodes D1 and D2), When the threshold is exceeded, the voltage regulator is switched on. The cycle repeats itself.
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