Part Number: TLC77
I am using TLC7701IPW device in our current program. We have connected 22uF, X7R capacitor to CT pin to provide 462ms delay as per the formula 2.1 x 10000*Ct. But I have tested at Ambient this circuit on 5 boards, I got delay around 690ms which is not supposed to be. Even if I consider 20% of capacitance tolerance (X7R is 10%) also, delay much not exceed 554ms. Please advise whether is there anything else needs to be considered for delay calculation. Immediate response is great appreciated.
Hi RANGA SWAMY K,
We are investigating this issue. I believe the max delay allowed for this device is 2.1ms typical (4.2ms MAX) which corresponds to a delay capacitor = 0.1uF. This is because of the time it takes to charge and discharge the capacitor. The charge current is 50uA and the charge voltage is 1.1V. If you put a larger capacitor, the capacitor doesn't have the time to discharge completely so the delay is longer than expected (and not accurate).
If you need a delay of 462ms, I will recommend using one of our newer devices such as TPS3808 with programmable delay between 1.25ms to 10s or TPS3890 with programmable delay between 40us to 30s. Would either of these devices work for your application?
In reply to Michael DeSando1:
In reply to RANGA SWAMY K:
I finally got the bench testing done and using 22uF, I saw a delay of 610ms. I then switched to the value capacitor used in the datasheet (100nF) and saw a delay of 2.9ms (which is within the min/max range of 1.1ms and 4.2ms). I spoke to the designers and they said there is no max value capacitor limitation. This leads me to believe that the wide range of the delay to begin with plus the tolerance of the capacitor can produce a valid delay higher than the typical calculated delay from the equation. The equation only gives a typical estimation but can't give a min/max tolerance for the actual delay.
I recommend changing the capacitor value to match the delay you want (and verifying the delay is the desired value) or you can switch to one of our higher accuracy devices. We have a lot of newer devices with much better threshold and delay accuracy.
Please refer to the "Programmable Delay" section in the Supervisor and Reset IC reference guide:
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