overshoot problem of EPM7128S

[Jian Ju]

Hi,

I have a project where one of the output signals is a short pulse with a
width of 100ns and repeat frequency of 1MHz. The main clock in my design is
20MHz. After I download the program to the chip (EPM7128SLC-7) severe
overshoots (over 2V @VCC=5V)can be observed. Does anybody know an answer to
this problem? Thank you.

--
Regards,
Jian

 

[Krzysztof Szczepanski]

Uzytkownik "Jian Ju" <jianju.ee@polyu.edu.hk> napisal w wiadomosci
news:1069903547.946685@hkpu01...

Hi,

I have a project where one of the output signals is a short pulse with a
width of 100ns and repeat frequency of 1MHz. The main clock in my design
is
20MHz. After I download the program to the chip (EPM7128SLC-7) severe
overshoots (over 2V @VCC=5V)can be observed. Does anybody know an answer
to
this problem?

A serial inductance at the power path can do the overshoots or a switching
power supply generates pulses of voltage at times where large current
changes are observed (shortcut to ground or VCC at output pin).

Regards,
krzysiek

 

[Ben Twijnstra]

Hi Jian,

I have a project where one of the output signals is a short pulse with a
width of 100ns and repeat frequency of 1MHz. The main clock in my design
is
20MHz. After I download the program to the chip (EPM7128SLC-7) severe
overshoots (over 2V @VCC=5V)can be observed. Does anybody know an answer
to
this problem? Thank you.

This could be due to ground bounce or a badly matching trace impedance. I
suggest that you turn on the 'Slow Slew rate' for this pin. It will make the
level transitions of the pin slower by about 1ns (it's a bit asymmetrical)
so that the device doesn't 'pull as hard' on the line.

If that doesn't help, get back to us.

Best regards,


Ben