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initial startup delay for TPS2490
My name is vengat from Avnet , one of my customer is using TPS2490 Hot swap controller product in their design & they want to make a initial start up delay of 118 ms for TPS2490 device , how we can achieve the 118 ms delay in EN Pin or TPS2490/91 ? . Any calculation is required to put RC combination ? Any one has application can you shared with me ..i would really help me to move it forward .
TPS3808 has programmable delay function through external capacitor on Ct pin. Use the RESETx output to connect to TPS2490 EN pin. You'll need an intermediate voltage supply for the TPS3808.
I possible simple solution might use a TLV809xxx operating from a resistor divider and driving the EN pin.
Since the TLV809 supply current is quite small, you can reduce its effect with a much larger bias current in the divider; compensating for teh nominal supply current yields the next level of accuracy.
The TLV809 has a fairly wide reset time tolerance, however it in in the order of magnitude the customer wants. In addition, a lot of issues of input voltage droops, recovery time etc. can be solved using a part like this.
Thanks , i will suggest to my customer & would update u.
Above combination will support 300 ms delay with TPS2490 ? ( The output should come up after 300 ms after power on.).
Do you have any Reference schematic or in TINA Model ?
They want to achive 300 ms delay in TPS2490 but above combination of ( TPS3808 + TPS2490 for 300 ms delay )will not work because input power start from 9 V and they do not have any other input DC rail . it is possible to achive RC combination in EN Pin ? Do you have any calculation for 300 ms ?
TPS3808 could be powered from the 12V input using either 12V-> 3.3V LDO or simple resistor + zener diode as regulator. Alternatively, the simple R-C circuit tied to the EN pin could also be used.
R x C = 0.3s / (ln (1-Ven/Vin))
Ven is EN pin trip point (1.35V typical) and Vin is the input voltage turn on (9V). You probably want to adjust depending on Ven, Vin, R, and C tolerances too.
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