TPS3890: TPS3890 Delay Time

Hirotsugu Kobayashi,

We have not tested longer delays than 30s. There are two items to note when using a larger capacitor than 26uF.

1. When using larger capacitors, assuming a 10% tolerance, there will be a lot more variation from nominal value to acutal value which could produce more error.

2. When the /RESET is asserted, the capacitor must discharge. When the device is no longer in undervoltage condition, the capacitor begins to charge up to the reference voltage to produce the reset delay. By adding larger capacitance, its possible that the capacitor is not able to discharge completely when the RESET first activates to logic low which means that when the device is no longer sensing undevoltage condition, the capacitor will begin charging a capacitor that has not been completely discharged which will produce a short reset delay than detected. The additional capacitance will add slight delay to the high-to-low output propagation delay as well.

If you test thoroughly and understand the effects of adding additional capacitance, you can use larger than 26uF for delay capacitor. I hope this answers your question. In summary, you can use larger capacitor but will produce shorter delays if the device triggers a reset then no longer senses an undervoltage condition before the capacitor can discharge.

-Michael