• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 22 subscribers
  • Views 526 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

SN74HC02: Comparing SN74HC02PWR and SN74HC02PWRE4

Tri Nguyen
Prodigy 10 points
Part Number: SN74HC02
Other Parts Discussed in Thread: SN74LVC1GX04, SN74HCU04

In the past we have ordered SN74HC02PWRE4, and designed a clock circuit with it. Recently it appears we have been ordering SN74HC02PWR and it may be causing issue with our circuit. We are guessing it's a impedance mismatch. We are attempting to create a circuit that produces a 4Mhz signal, with the recent part SN74HC02PWR it has failed to do so only producing about 68Khz.  I have looked at both spec sheets and could not find a difference in characteristics.

I was wondering if there is a difference between these two parts. 

Below is a section of circuitry that we are trying to make.

U88 is the component in question. It is receiving a 5V VCC the circuit powers a clock signal to 6 other devices, they are not causing this error.

below are some captures

This is the expected waveform at Pin 11/12 using SN74HC02PWRE4

  • Frequency is 4 MHz
  • Pk-Pk is about 4.8V

This is the waveform at Pin 11/12 using SN74HC02PWR 

  • Frequency is 38.37 kHz.
  • Pk-Pk is about 1.04V

Below is the output Pin 13 using SN74HC02PWRE4

  • Frequency is 4 MHz
  • Pk-Pk is about 8.4V
  • Rise time is 3.8ns

Below is the output pin 13 using SN74HC02PWR 

  • Frequency is 67.16 kHz.
  • Pk-Pk is about 8.48V
  • Rise time is 3.67ns

When changing the resistor R184 from 1M to 100k ohms, this fixes the issues, but I cannot proceed with the changes unit I determine what may have caused this. Changing a resistor might suggest in changes in impedance within the SN74HC02PWR .

Hope to hear from you soon.

  • 0
    TI__Mastermind 38085 points

    Hi Tri,

    Due to a US holiday, our team will get back to you tomorrow. 

  • 0
    TI__Mastermind 26140 points

    Hi Tri,

    There is no difference in electrical characteristics between the two parts. 

    Have you measured the pin impedance to ground to confirm if there is an impedance mismatch or not? I suspect the impedance of both pins will still be within the same order of magnitude as the other device. 

    It's also possible having R185 in series with R184 instead of in parallel is interfering with the output of the crystal oscillator.

    Best,

    Malcolm

  • 0
    Guru 316920 points

    There is no difference between devices with and without -E4; see [FAQ] Why does a logic device's part number have an E4/G4 suffix?

    However, TI has begun switching to a new design (see PCN#20200629000.1), which has some hysteresis at the inputs. This makes no difference in the characteristics guaranteed by the datasheet, and improves behaviour for digital signals, but makes it impossible to use it as an analog amplifier. In a Pierce oscillator, you must use unbuffered inverters, e.g., SN74HCU04 or better SN74LVC1GX04.