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I have always used level translators when communicating between 2 systems(or controllers) of different voltage levels. For eg txb0108 is a commonly used one, among a host of others. Now, why should one use such an ASIC. Why can the same be not done using a voltage dividor or such a simple and cheap component ? What is the major game changing advantage when we use such dedicated ASICs ? Ofcourse, these ASICs might come power packed with buffers and such facilities, but if it was a straighforward voltage level lowering can the resistors suffice ?

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    \$\begingroup\$ If you know what load to drive and how it affects signal integrity, you might be able to get away with a divider, but in most cases you either don't know or the signal integrity crapsout. \$\endgroup\$
    – PlasmaHH
    Oct 21, 2015 at 10:58
  • \$\begingroup\$ could you kindly explain please ? \$\endgroup\$
    – Board-Man
    Oct 21, 2015 at 10:59

3 Answers 3

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"Why can the same be not done using a voltage dividor or..."

Because a voltage divider consisting of 2 resistors:

  • can only interface between a higher voltage to a lower voltage, for example: 3.3 V to 1.8 V
  • the divider forms a resistive load, when a signal is 1 a current flows. This is unacceptable for low power applications.
  • it only works properly at the input/output voltage ratio it is designed for so a divider for 3.3 V to 1.8 V might not work for 3.3 V to 2.2 V
  • The impedance level of the output signal increases because it comes through a resistor, not from a low impedance output. This is problematic for high frequency signals.

Proper levelshifters don't suffer from these disadvantages.

So in general: no, a resistive divider cannot replace a proper levelshifter. Maybe in some applications it can but be prepared for all the disadvantages listed above. Is is worth that ? I would say no and just use a levelshifter.

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  • \$\begingroup\$ True. To be more precise, an other similar divider can be made for 3.3 to 2.2 Volts too, but resistor values have to be changed. \$\endgroup\$
    – Szundi
    Mar 15, 2022 at 7:01
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This is my favorite simple levels shifter circuit. It's bidirectional and everything. enter image description here

The only real downside is a semi decent driver is required, a weak one won't cut it.

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  • \$\begingroup\$ The thing is that he wants passives, not just discretes. So what this question really needs as an answer is a tuturial on signal integrity. \$\endgroup\$ Oct 21, 2015 at 11:08
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    \$\begingroup\$ @RespawnedFluff Bidirectional level shifting is not possible with only passive components. To directly replace the txb0108 at least one discrete is required. \$\endgroup\$
    – vini_i
    Oct 21, 2015 at 11:13
  • \$\begingroup\$ Alas it's unclear from the question if he even wants bidirectional... \$\endgroup\$ Oct 21, 2015 at 11:20
  • \$\begingroup\$ yes I get your point. But suppose I need to merely step down a voltage then, can I not do it using a voltage divider ? \$\endgroup\$
    – Board-Man
    Oct 21, 2015 at 11:21
  • \$\begingroup\$ Not bidirectional. Just uni directional. \$\endgroup\$
    – Board-Man
    Oct 21, 2015 at 11:21
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Eh, unidrectional high-to-low can be done with resistors and diodes https://www.maximintegrated.com/en/app-notes/index.mvp/id/3007

enter image description here

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