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Method to create a power turn on and turn off sequence without a reset IC or PLD

The power turn on and turn off sequence is becoming more complicated in recent years. THine Electronics’ power solution, however, has made it possible to achieve it easily, contributing to reduction in customers’ total cost of system development.

Power sequence increasingly complicated on boards

For LSI, such as FPGA, SoC, ASIC, MCU, and DSP adopted in various applications in recent years, different power supply voltages, more than one, are required, such as 1.0V, 1.2V, and 1.8V.  Because of this, designers have to prepare two power supply rails or more. The order to turn on/off the power supply rails is called the power sequence. Basically, the turns on from a power supply rail of lower voltage to that of higher voltage for the turn-on sequence, and the  turns off from a power supply rail of higher voltage to that of lower voltage for the turn-off sequence.
 
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However, all LSI presently used in the world are not necessarily unified by this rule. There is even a case that the reverse rule is applied. In fact, the order and timing of turn on/off are different for each LSI.

Usual methods of sequence creation lead to a cost increase

Regarding the  turn-on timing, power supply is generally activated by the power good function and the ON/OFF (CTL) function, which the power supply is equipped with. 
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The power good function sets a flag when the output reaches a preset voltage. This enables designers to create  turn-on sequences for several power supplies by combining the power good function with the ON/OFF (CTL) function. Even a sequence control that uses a tracking function (simultaneous / proportional / offset) is not unusual recently.

However, among sequence requirements for some LSI, there are cases where customers ask for a specific  turn-off timing. To answer to this request, a dedicated sequence IC or reset IC needs to be added, thus presenting a cost-raising factor.
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By using a power supply product with an off-delay function, a sequence up to turn-off can be developed at a low cost

zoomTHV81800, a power supply product from THine Electronics, is loaded with an off-delay function.

 
This off-delay function sets a time until output becomes off after the ON/OFF (CTL) terminal is switched from “High” to “Low.” The power becomes off in conjunction with the ON/OFF (CTL) terminal, but a delay time until power starts turning off can be created by connecting the off-delay terminal with a condenser.

 


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By using a product that has such a function, it will be possible to simplify the circuit, reduce the number of parts, and shorten the development lead-time.

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