SN74LV14A: About Interface

soichiro kikuchi

Prodigy 250 points

Part Number: SN74LV14A
Other Parts Discussed in Thread: SN74LV86A, SN74HCS244

Tool/software:

Are both of the two combinations shown in the diagram above OK?

3 months ago

0 Clemens Ladisch 3 months ago

Guru 316960 points

Yes.

(The input leakage current of CMOS inputs is extremely small, so those V_OL/V_OH limits do not matter; the actual output voltages will be near GND/V_CC.)

0 soichiro kikuchi 3 months ago in reply to Clemens Ladisch

Prodigy 250 points

Even so, the Vcc of the LV14A should not be 5V, right?(Although it may work with real ability)

Even if the Hi level is almost 5V, the HCS244 cannot be received, right?

0 Malcolm Lyn 3 months ago in reply to soichiro kikuchi

TI__Mastermind 26140 points

Input pins on the LV14A are overvoltage tolerant, so they can receive 5V inputs from the HCS244 with no issue.

0 soichiro kikuchi 3 months ago in reply to Malcolm Lyn

Prodigy 250 points

Sorry, my question is this combination.

Vcc can be 3.3V or 5V, but only one of them. (Because the board is common)

0 Clemens Ladisch 3 months ago in reply to soichiro kikuchi

Guru 316960 points

HCS inputs are not overvoltage tolerant, so the connection from the SN74LV86A will not work.

0 soichiro kikuchi 3 months ago in reply to Clemens Ladisch

Prodigy 250 points

It means that the input voltage is less than Vcc.

0 Malcolm Lyn 3 months ago in reply to soichiro kikuchi

TI__Mastermind 26140 points

If both devices are 5V VCC, this application is fine. If a device's recommended operating conditions state 0 to VCC, the input voltage to that device must not exceed VCC or you risk damaging the device.

0 soichiro kikuchi 3 months ago in reply to Malcolm Lyn

Prodigy 250 points

If the VOH of the SN74LS86 is 2.4V and the VT+ of the SN74HCS244 is 3.15V, is the SN74HCS244 not recognized as hi?

When VCC is 5V, is the maximum value of VT+ 3.5V?

+1 Clemens Ladisch 3 months ago in reply to soichiro kikuchi

Guru 316960 points

Correct. You would need a pull-up resistor for this to work.

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SN74LV14A: About Interface