About Output inpedance of SN74LVC04A

Satoshi

Guru 19485 points

Other Parts Discussed in Thread: SN74LV04A, SN74LVC04A

Please let me know about LVCMOS output inpedance(Zo) of SN74LV04A.

【Background and condition】

・SN74LVC04A using for clock driver(50MHz)

・Inpedance matching of this pattern is 40～50Ω

・Output side is connected 22Ω-danping for waveform shaping.

⇒Customer want to know these circuit is maching or not.

Best regards,

Satoshi

0 Emrys Maier over 7 years ago

Hi Satoshi-san,

A 50 ohm load on this part will exceed the part's drive capability (max of ~12mA at 3.8-V Voh)

My math:

Vo / Rload = Imax (maximum output current required)

5V / 50ohm = 100mA

If Voh were to dip to 3.8V (lowest value listed on datasheet),

3.8V / 50ohm = 76mA

Since the part can only output ~12mA max, I would recommend looking into a different solution.

Can you tell me more about your application?

0 Emrys Maier over 7 years ago in reply to Emrys Maier

Correction*

The output will have to source half of what I listed, but 50mA and 38mA are still much higher than what the device can handle.

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