Technical Information Site of Power Supply Design

2022.06.22 DC/DC

Power Supply Sequence Specification②:
Sequence Operation at Power Turn-on

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

In the previous article, the power supply sequence specification ② to be implemented, and the circuit configuration using control blocks, were confirmed. Here, sequence operation at power turn-on is examined.

Power Supply Sequence Specification②: Sequence Operation at Power Turn-on

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. The sequence operation at power turn-on is explained following the order (shutoff is explained the next time). In this explanation, the operation in which 1.2 V is turned on is the first stage, the 1.5 V turn-on operation is the second stage, the 3.3 V turn-on operation is the third stage, and the state in which all three systems are turned on is referred to as the power supply operating state. In diagrams of each of the stages, the part relevant to the explanation is shown 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", 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".

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 1.5 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 3.3 V, all of the power supplies with three supply voltages are operating (See the figure below “States of the main nodes during power supply operation”).

The above is the sequence operation at power turn-on for the power supply sequence specification ②. Next time, the sequence operation at power shutoff will be explained.

Key Points:

・In sequence ②, three power supply systems are turned on in order, and are shut off in the same order.

・In order to aid understanding of sequence operation, the operation at the time of turn-on of each of the three power supply systems is shown separately.

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