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SN74LVC1G04: SN74LVC1G04

Part Number: SN74LVC1G04
Other Parts Discussed in Thread: SN74LVC1G14, TLV3201

It is nice to know TI's experts here. I am thinking the application of SN74LVC1G04.I have some questions.

(1)What's differences between the SN74LVC1G14 and the SN74LVC1G04?

(2)In the datasheet of SN74LVC1G04,I see the discription" Ioff Supports Live-Insertion, Partial-Power-Down Mode, and Back-Drive Protection".

I wonder in which condition Ioff functions?When a SN74LVC1G04 is power by 3.3V, Ioff will function?

(3)One of my freiends used SN74LVC1G04 as a waveform transfomatin,for example transforming a  sine waveform to a Square waveform.

A typical circuit is as Picture1.

                   Picture1. Application Circuit of the SN74LVC1G04

The input signal of the SN74LVC1G04 is a 10MHz Sine waform with a  DC bias as Picture 2.

                                   Picture 2.  Input signal of  SN74LVC1G04 (after a 1nF Cap)

Original Input signal is a 10M sine waform with a  DC bias as Picture 3.

                                           Picture 3.  Souce of Input signal of  SN74LVC1G04 (before a 1nF Cap)

Actually,he made the NC pin(Pin1) and the input pin(Pin2)  of the SN74LVC1G04 short on PCBA.Then,he adjusted the amplitude of DC bias of

the sine waveform to 1.52V(not 1.65V). Then some of the products failed in customer's site.Some SN74LVC1G04 ocassionally outputed 0V

(not a 10M Square waveform) when the input was normal( as a 10MHz Sine waform with DC bias) .Or several  SN74LVC1G04 outputed abnomal

Square waveform whose duty ratio was out of the range(45%~55%).

We don't know why the failure occured in the fied.Hope TI's expets give some advice,Thans very much! 

  • Difference bw SN74LVC1G04 and SN74LVC1G14 is the Schmitt trigger function of SN74LVC1G14. The 1G04 function is a basic inverter without ST.

    The LVC1G04 has recommended spec limits on the input transition rates of a signal as given in the ROC. With that said, the LVC1G04 cannot handle slow rising edges like the sine waves. The LVC1G14 with its Schmitt trigger property includes defined hysteresis allowing slow rising edges and can handle sine wave to square wave.

    The DC bias also must be ensured such that the signal crosses the Vt+max and Vt-min values to ensure a output transition.

  • 1. The '14 has a Schmitt-trigger input.

    2. The Ioff feature allows voltage at the I/O pins when the device is powered down. So it works only when VCC is 0 V.

    3. The sine wave is not a valid logic signal, and might prevent the device from working, or even damage it. See [FAQ] How does a slow or floating input affect a CMOS device? You need to use a device with a Schmitt-trigger input to prevent damage, but that does not guarantee that the switching threshold is exactly in the middle. To be able to better control the switching threshold, you have to use a high-speed comparator (e.g., TLV3201).

  • Thanks for your reply.

    I cheked the datasheet of  SN74LVC1G04, in my opinion we can use SN74LVC1G04 as a comparator at a frequence of 10MHz.

    However,we should pay more attention to the applicaton of SN74LVC1G04 when we use it as a waveform transformor.

    Several questions disturbed me.

    (1)If the NC pin and the Input pin of the SN74LVC1G04  are parallelled with a 10MHz sine waveform(as Pic1 showed),did SN74LVC1G04 function nomal?

    Is there any issue about this application(for example,signal reflection)? 

    (2)As for SN74LVC1G04, what's the limitation of rising or falling speed of the input signal?Or how do I know the slowing rising speed of the Input signal?

    (3)How to judge a SN74LVC1G04 nomal or malfunction on a PCBA?

    (4)What's more,could you tell me the differences between SN74LVC1GU04 and SN74LVC1G04.

    Actually I saw a mature product which used the SN74LVC1G04 as a waveform transformor. The Input signal of  SN74LVC1G04 is a 10MHz sine waveform(as Pic1 showed),and the output signal is a 10MHz square waveform(as Pic2 showed).

                                                          Pic1 Input signal of N74LVC1G04 in a mature product

                                                                  Pic2 Onput waveform of N74LVC1G04 in a mature product

                                                         Pic3 Onput waveform of N74LVC1G04 in a returned product

  • NC pin is not connected to the die or to the internal circuit.

    LVC1G04 as I have mentioned doesnt have schmitt trigger inputs to tolerate slow edges ( sine waves).

    From the recommended operating conditions of the datasheet page, the input transition rate is 10ns/V for 3.3Vcc. You have > 50ns in this case.

    From the scopeshot you have sent, the low is ~1.2V and the high is ~2V.

    From the ROC table of the datasheet, the Vih is 2V min and Vil is 0.8V max ; which means that the device must have inputs lower than 0.8V to be recognized as logic low and above 2V to be valid high level. The device may work sometimes but it is not guaranteed to work always as the specs are being violated.

    The signal has to cross both the logic thresholds to be considered valid / recognized by the device.

    LVC1GU04 - U stands for unbuffered inputs.

    Refer to the app note on the buffered vs unbuffered inputs