SN74LV4T125: Schematic of SN74LV4T125

beesetty rajesh

Part Number: SN74LV4T125
Other Parts Discussed in Thread: SN74LVC3G17, ULN2003A, TPL7407LA, CD4504B, CD40109B, UCC27517

Hello TI,

I have an applications where 3.3V to 5V and 5V to 3.3V is required

I selected SN74LV4T125 for both the cases.

Kindly let me know if any mistakes I did in the schematics.

over 3 years ago

0 Clemens Ladisch over 3 years ago

Guru 244220 points

This looks OK.

It is common to also use smaller decoupling capacitors (typcially 100 nF).

For level shifiting from 5 V down to 3.3 V, you could replace U27 with a buffer with overvoltage-tolerant inputs, e.g., SN74LVC3G17, which has a smaller package.

If you replace the ULN2003A (U16) with a TPL7407LA, you do not need to shift the 3.3 V signals to a higher voltage and can drop U24.

0 beesetty rajesh over 3 years ago in reply to Clemens Ladisch

Expert 1055 points

Thank you for your reply and invaluable suggestion.I'll go for TPL7407LA.

I am also looking for an IC to shift voltage levels from 3.3V logic to 15V logic to generate PWM pulses of 10kHz frequency. Minimum propogation delay is desired. I tried to search in the TI's level shift logic page but couldn't get! Kindly suggest any IC if any.

waiting for your reply.

0 Clemens Ladisch over 3 years ago in reply to beesetty rajesh

Guru 244220 points

The only logic family going above 5 V is CD4000. Check out the CD40109B or CD4504B.

0 beesetty rajesh over 3 years ago in reply to Clemens Ladisch

Expert 1055 points

I'd like to have a confirmation from you regarding the OE pins which are grouped and connected to the ground.

0 beesetty rajesh over 3 years ago in reply to Clemens Ladisch

Expert 1055 points

Hello Ladisch,

I'd like to know what could go wrong if I choose SN74LV4T125.

0 Clemens Ladisch over 3 years ago in reply to beesetty rajesh

Guru 244220 points

With the OE pins connected to ground, the four buffers will be always active. (Even during power up, when the input might not yet be valid.) The behaviour is the same as with a buffer without OE, e.g., the SN74LVC3G17.

0 beesetty rajesh over 3 years ago in reply to Clemens Ladisch

Expert 1055 points

Hi Clemens,

As you recommended CD40109B or CD4504B for 3.3V to 15V transition, But the datasheets says that its typical input voltage is 5V. Kindly confirm the IC.

0 Clemens Ladisch over 3 years ago in reply to beesetty rajesh

Guru 244220 points

The CD40109B allows voltages down to 3 V in the recommended operating conditions on page 1. I assumed that the CD4504B also supports this, like most other devices in the CD4000 family, but that appears not to be the case.

You could also use an entirely different device, e.g., a gate driver with TTL input like the UCC27517.

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SN74LV4T125: Schematic of SN74LV4T125