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Good morning everyone,

I have a STM32F407 microcontroller running on 3.3V logic level, and I have a plethora of peripherals that I want to connect to it. The problem is that these peripherals run at anything but 3.3V level. Some of them are 1.8, some are 2.5, and a couple of 5V devices.

Immediate solution that comes to mind: programmable logic level translator. There are a lot of dual supply bi-directional level translator ICs available; I can turn these into "programmable" ones with the help of digital potentiometers.

My only problem is the common requirement of logic level translator ICs: Vcc > Vl, i.e. voltage on one side of the translator must be strictly less that voltage on the other side. But what I want is:

controller side logic level: fixed at 3.3V,

GPIO side level: anything from 1.8 to 5 V.

Are there any solutions to this problem (either through ICs or discrete elements), or am I asking too much? Thank you in advance.

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  • \$\begingroup\$ Why do you want to use the same translator for each peripheral? \$\endgroup\$ – CL. Aug 11 '15 at 7:15
  • \$\begingroup\$ @CL ideally - yes; in short, the question is about the ability to level-shift a single signal line (or a pair of such) in a wide range of voltages. \$\endgroup\$ – Dmitriy Khudorozhkov Aug 11 '15 at 7:20
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    \$\begingroup\$ Can the peripherals provide the voltage to power the level shifter? That would allow you to have the right level without any configuration. \$\endgroup\$ – Botnic Aug 11 '15 at 7:25
  • \$\begingroup\$ @Botnic - I guess no, as most of 'em are sensors (I provide voltages for them via separate power rails). \$\endgroup\$ – Dmitriy Khudorozhkov Aug 11 '15 at 7:31
  • \$\begingroup\$ @DmitriyKhudorozhkov, that doesn't make your point. If you can supply each sensor with its required voltage, you can also supply that voltage to the level translator. \$\endgroup\$ – The Photon Aug 11 '15 at 8:49
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One option is, design your system to accommodate translation from 3.3 V on the uC side to lower and equal voltages on the peripheral side.

Then if you have a 5 V peripheral, include as part of the peripheral circuit a translator to translate from 5 V on the peripheral side to 3.3 V on the uC side. This means that 5 V peripherals will have their signals running through two translator circuits.

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If your 5V peripherals are inputs to the uC, then using a device from the 74LCX series can help. These devices are designed to have 5V tolerant inputs in a 3.3V system.

You may need to watch out for the Volp (quiet output bounce) specification. This is a measure of how much disturbance a quiet output experiences when any other output changes state.

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