CD74HC123: functioning : by detecting the Negative pulse on 1st pin, It should generate high level pulse on 13th pin.

anandam boora

Part Number: CD74HC123

Hello,

we used CD74HC123E as mono stable by using input pin 1( -1A) and Output Pin 13( 1Q). Input negative pulses will receive by motion sensor and output goes on for 21 seconds. So this solution is used in our street light product and we sold almost morethan 25000 lights in to the market.But after 3 or 4 months the problem reported by customer is light blinking.So we rectified by replacing the IC, But as per our analysis on faulty IC the IC pins 16(VCC, 5VDC) and 15(1RxCx) shorted and shown 16Ohms to 22ohms instead of 680ohmd in continuity mode of Digital multimeter.The percentage of failure is 3%. But why it is happening in IC internally, we need to understand how can we avoid the problem? we need solution urgent pls.

With Regards,

Anandam boora

Intelizon Energy Pvt Ltd.

Road No. 3&5, Banjara hills, Hyderabad-34, India.

anandam.br@gmail.com; anandam.b@intelizon.com

+91-9346116230;

over 6 years ago

0 Dylan Hubbard over 6 years ago

TI__Mastermind 43380 points

Hi Anandam,

Could I get a schematic of the system so I can see how you have the device implemented into your system. Also could I obtain some scope shots of normal operation with the Input, Output, and VCC probed (if you have a current probe, having the ICC measured in that scope shot would be great as well). With those things I can further help debug this issue thanks.

0 anandam boora over 6 years ago in reply to Dylan Hubbard

Prodigy 120 points

Hi Dylan,

Attached is the Schematics, here the 1st pin of 74HC123E is -Ve input pulse and ouput on 13th pin is positive pulse to drive the transitor. Here the time intervel is fixed for 21seconds but shown only few msec pulse on output. Pls see the schematics and give the solution to avoid this problem in the field and it is not in all systems some 3% only that to 3months after installation.

with Regards

anandam Boora,

Intelizon Energy Pvt Ltd.

Road No. 3&5, Banjara Hills,

Hyderabad-500083.

anandam.br@gmail.com; anandam.b@intelizon.com

0 Dylan Hubbard over 6 years ago in reply to anandam boora

TI__Mastermind 43380 points

Hi Anandam,

I can't really read anything from that image, is there not a way to get a clearer schematic image? Also are you not able to get me scope shots?

0 anandam boora over 6 years ago in reply to Dylan Hubbard

Prodigy 120 points

0 Dylan Hubbard over 6 years ago in reply to anandam boora

TI__Mastermind 43380 points

Hi Anandam,

Thanks for those scope shots I can clearly see the issue you are having now. Any way I can get a clearer schematic, it is important for me to see how the device is implemented including the values of the passive components used.

0 anandam boora over 6 years ago in reply to Dylan Hubbard

Prodigy 120 points

0 Dylan Hubbard over 6 years ago in reply to anandam boora

TI__Mastermind 43380 points

Hi Anandam,

Thanks for that schematic I can see everything clearly. I didn't see issues with anything in the schematic except leaving the inputs floating for the second mono. Its never good to leave input floating for a CMOS device. I can't determine if that is the cause of this issue. One more scope shot that would help is to measure across C9 for a working device and a failing device during operation to see the charging/discharging of the capacitor. I also recommend going through your distributor to start a FA (failure analysis).

0 anandam boora over 6 years ago in reply to Dylan Hubbard

Prodigy 120 points

0 anandam boora over 6 years ago in reply to anandam boora

Prodigy 120 points

Any issue when soldering the IC, like temp and other things. pls give the details for part failure possibilities.

0 Dylan Hubbard over 6 years ago in reply to anandam boora

TI__Mastermind 43380 points

Hi Anandam,

I don't see any possible issues when it comes to soldering except for possible ESD strikes. Thanks for those scope shots they helped me confirm a few things: The capacitor is too big and the driver isn't able to discharge it all the way to 0V. Not only that, it means there is a lot of charge going through the device which is most likely stressing it. This with the addition of leaving the inputs floating could all be possibilities for failure.

There is a better way to get a 21 s pulse like this using a ring oscillator and a counter. Would you be open to the idea of that?

0 anandam boora over 6 years ago in reply to Dylan Hubbard

Prodigy 120 points

Pls suggest the cap and resisitor to get the 21S pulse and what pins need to pulled up what pins need to pulled down pls suggest on our existing circuitry. The Cd74HC123 part is suggested by Panasonic make application note of Motion sensors.

Regards

anandam boora

0 anandam boora over 6 years ago in reply to Dylan Hubbard

Prodigy 120 points

pls suggest us which values of cap and resisitor to be used for 21 Seconds pulse. And what inputs to be connected to VCC and what inputs to be connected to Gnd. pls suggest us.

0 Dylan Hubbard over 6 years ago in reply to anandam boora

TI__Mastermind 43380 points

Hi Anandam,

You have the right values for a 21 second pulse. You are just operating at its boundaries. You would want to reduce the cap size, but you will have to increase the resistor size. Having this too large could also cause some issues because there will be some leakage current causing a voltage drop. As for the inputs you can just ground them.

0 anandam boora over 6 years ago in reply to Dylan Hubbard

Prodigy 120 points

How to screen the ICs in incoming goods and how to test the IC functionality while assembly process and any special instructions required. Pls give the details.

0 Dylan Hubbard over 6 years ago in reply to anandam boora

TI__Mastermind 43380 points

Hi Anandam,

I don't quite fully understand what you are asking. There aren't any special instructions and a good way to test is to basically follow the steps that we took to debug this issue. If you are wanting to decrease that capacitor and increase the resistor, my recommendation is to make sure that the voltage is dropping too much from VCC due to the leakage current.

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CD74HC123: functioning : by detecting the Negative pulse on 1st pin, It should generate high level pulse on 13th pin.