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2021.10.13 DC/DC

Power Supply Sequence Specification ①: Sequence Operation at Power Turn-on

Circuits to Implement Power Supply Sequences Using General-Purpose Power Supply ICs

In the previous article a control circuit for the "Power Supply Sequence Specification ①" was presented. Here, we first explain the sequence operation when power is turned on.

Power Supply Sequence Specification①:Sequence Operation at Power Turn-on

As explained previously, in the sequence for Specification ① the outputs of the three power supply systems for 1.2 V, 3.3 V, and 1.5 V are turned on in order. The sequence operations are explained in order. In the explanation, the operation in which 1.2 V power-on occurs will be referred to as the first stage; similarly, the 3.3 V turn-on operation is the second stage, the 1.5 V turn-on operation is the third stage, and the state in which all three power supply systems are turned on will be referred to as the power supply operating state. In diagrams of each of the stages, the part relevant to the explanation is shown in red.

In the initial state, with the Enable pin at "L" level, the three DCDC outputs are zero.

●Operation for first-stage power supply turn-on

  • 1) The Enable pin is set to "H" level to start the supply of power
  • 2) The EN pin of DCDC 1 goes to "H" via the diode D1, so that DCDC 1 is started.
  • 3) When the DCDC 1 output voltage rises from 0 V to 1.2 V, the Power Good 1 output changes from "L" to "H", and the EN pin of the next-stage DCDC 2 goes to "H".
  • 4) The diodes D2 and D4 cause "H" level to be applied to the IN pins of Power Good 3 and Power Good 4, so that the PGOOD pins (outputs) maintain high impedance.

● Operation for second-stage power supply turn-on

  • 1) The EN pin of DCDC 2 has gone to "H", and so DCDC 2 starts.
  • 2) When the DCDC 2 output voltage rises from 0 V to 3.3 V, the Power Good 2 output changes from "L" to "H", and the EN pin of the next-stage DCDC 3 goes to "H".

●Operation for third-stage power supply turn-on

  • 1) The EN pin of DCDC 3 has gone to "H", and so DCDC 3 starts.
  • 2) When the DCDC 3 output voltage rises from 0 V to 1.5 V, all of the power supplies with three supply voltages are operating (the states of the main nodes during power supply operation are shown separately).

In the next article, sequence operation upon shutoff will be explained.

Key Points:

・In Sequence ①, power supplies with three supply voltages are turned on in order, and are shut off in the reverse order.

・In order to aid understanding of the sequence operation, the operations for turn-on of the three power supply systems were presented separately.

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