SN74LVC1G175-EP: Output Q does not reach high level, when CLK changes from L to H

Bui Hoang

Prodigy 20 points

Part Number: SN74LVC1G175-EP

Tool/software:

Hello support team,

I am using D flip flop with part number: CLVC1G175MDCKREP.

My problem: The Q output doesn't go high.
Description: On the circuit I am soldering R244 = 20K, C383 = 22uF, D27 not fitted. The #CLR signal reaches a high level, after about 4.3 seconds CLK changes from Low to High. However, the Q pin still remains low.
I have soldered a push button in parallel with C383, if I press it then Q goes high.

Please let me know the problem and solution.

Thanks for supporting me,
Regards!

over 1 year ago

0 Clemens Ladisch over 1 year ago

Guru 321620 points

Please also show the A input of U40, and the Q output.

0 Bui Hoang over 1 year ago in reply to Clemens Ladisch

Prodigy 20 points

Hi Sir,

Please see attached photo below.

I have measured on U42 - A input and U41 - CLK input. After CLK goes high for about 3ms, U42 - A input has a pulse of about 30us, causing U41- #CLR to pull down to a low level of 30us.

I think this is the main reason.
I made 1 filter by, R245 = 182k and 1 capacitor in parallel = 30pF.

However, it has not been resolved.

I hope to receive a solution from you soon.

Thanks!

0 Clemens Ladisch over 1 year ago in reply to Bui Hoang

Guru 321620 points

So the problem is that U43 outputs a high pulse when it should not? Why? Where does the input signal of U43 come from? Is it noisy?

0 Bui Hoang over 1 year ago in reply to Clemens Ladisch

Prodigy 20 points

Hi,

Input signal of U43 from 1 SOC. I plugged the measuring stick in there and did not detect any abnormalities. I think, that pulse is 1 interference. Do you have a solution to this problem?

0 Clemens Ladisch over 1 year ago in reply to Bui Hoang

Guru 321620 points

That pulse does not look like noise, so I guess the problem happens at U43's input. Please show an oscilloscope trace of both the B input and the A output of U43.