Power Supply Sequence Specification ②: Sequence Operation at Power Shutoff

In the previous article, we explained sequence operation at power turn-on for power supply sequence specification ②. This time, we explain sequence operation at power shutoff.

Power Supply Sequence Specification②: Sequence Operation at Power Shutoff

As explained in the previous article, in the sequence for the specification ②, the outputs of the three power supply systems for 1.2 V, 1.5 V, and 3.3 V are turned on in this order, and are shut off in the same order. In this explanation, the operation in which 1.2 V is shut off is the first stage, the 1.5 V shutoff operation is the second stage, the 3.3 V shutoff operation is the third stage. In diagrams of each of the stages, the part relevant to the explanation is shown red.

●Operation for first-stage power supply shutoff

• 1) The Enable pin is set to “L” level to shut off the power supply.
• 2) The EN pin of DCDC 1 goes to “L”, so that DCDC 1 is shut off.
• 3) At the same time, the IN pin of Discharge 1 also goes to “L”, and so the OUT pin of Discharge 1 changes to low impedance. As a result, the output voltage of DCDC 1 rapidly shifts to 0 V.
• 4) When the DCDC 1 output voltage falls, the output voltage of Power Good 1 changes from “H” to “L”, and so the next-stage DCDC 2 EN pin and Discharge 2 IN pin go to “L”.

●Operation for second-stage power shutoff

• 1) The EN pin of DCDC 2 has gone to “L”, and so DCDC 2 shuts off.
• 2) At the same time, the IN pin of Discharge 2 also goes to “L”, and so the OUT pin of Discharge 2 changes to low impedance. As a result, the output voltage of DCDC 2 rapidly shifts to 0 V.
• 3) When the DCDC 2 output voltage falls, the output voltage of Power Good 2 changes from “H” to “L”, and so the next-stage DCDC 3 EN pin and Discharge 3 IN pin go to “L”.

●Operation for third-stage power shutoff

• 1) The EN pin of DCDC 3 has gone to “L”, and so DCDC 3 shuts off.
• 2) At the same time, the IN pin of Discharge 3 also goes to “L”, and so the OUT pin of Discharge 3 changes to low impedance. As a result, the output voltage of DCDC 3 rapidly shifts to 0 V.
• 3) With this, shutoff of all of the three power supply systems is completed.

The above is sequence operation at power shutoff for power supply sequence specification ②. In the next article, examples of an actual circuit and settings of component values etc. will be presented.