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SN74LVC3G04: SN74LVC3G14DCUR Icc to high with Vcc=5V and Input-Level=3,3V

Bernd Hafen
Prodigy 50 points
Part Number: SN74LVC3G04
Other Parts Discussed in Thread: SN74LVC3G14,

Hello,

I want use SN74LVC3G14 as a Level shifter. (Vcc=5V)

-          When I stet the Input to a 5V Level everything is Ok (Icc = 55uA)

-          But when I set the Inputs to 3,3V-Level the IC needs about 11mA per Channel, why?

Test:

(3-Ports = 0V, 0-Ports = 3,3V -> ~0,055mA)
(2-Ports = 0V, 1-Port = 3,3V -> ~11mA)
(1-Ports = 0V, 2-Ports = 3,3V -> ~22mA)
(0-Ports = 0V, 3-Ports = 3,3V -> ~33mA)

-         (extra) current flow into Vcc, not into the Inputs

-         there is no output resistor, current I(out)=0mA

-          The pinning on PCB is OK, because with 5V Inputs everything works correct!

-         I also tested it with „74HC3G14“ (Nexperia) on the same PCB this one works perfekt!

-          I also tested it with SN74LVC3G04 and it’s also the same problem as with SN74LVC3G14!

-          I testet it on different PCBs and it’s the same problem!

Other Test

-          Vcc = 3,3V = Input-Level=3,3V -> Icc = ~0,055mA undependet on any Input-Level, works perfekt

-          Vcc = 4,5V > Input-Level=3,3V -> Icc = ~1mA per Input_Channel High!

Markin Code ist "14CZ" (SN74LVC3G14DCUR VSSOP)

  • 0
    Guru 276400 points

    The "Recommended Operating Conditions" table says that the input voltage for a high level must be above 3.5 V.

    Anyway, if the input voltage is not near VCC, both input transistors turn partially on and short VCC to ground; see figures 7 and 8 of LVC Characterization Information (SCBA011):

    (This graph is for VCC =3.3 V; there is no documentation for 5 V, but you have already observed how that behaves.)

    This behaviour occurs for all CMOS families.

    To do level shifting, either use a family that has TTL-compatible inputs (e.g., AHCT, where the effect is smaller), or use an actual level shifting device.

    What drive strength and frequency do you need? Are inverters really necessary?