Hi,
The device used is TPS7A4700RGWR.
I try to check on the datasheet but could not find clear specification (min/typ/max) on the start up time from EN pin meeting the rising threshold to regulator start output.
In addition, what is the specification (min/typ/max) on the rise time of the output, based on 3.3V output config, output capacitor 47uF + 0.1uF and 1uF at NR pin?
Please help to advice. Thanks!
Regards,
Teoh
Hi Teoh,
The typical startup delay until the output begins rising is about 5 ms as shown in Figure 1 of the TPS7A47xx User's Guide. Please keep in mind that this startup delay is not a tested parameter and as such min/typ/max specs will not always be included in the datasheet.
http://www.ti.com/lit/ug/slvu741a/slvu741a.pdf
Equation 5 of the datasheet can be used to calculate the soft-start rise time of the output voltage. Again, this refers to the typical startup time as this parameter is not tested for min/max specifications.
Assuming you are using ANY-OUT configuration to achieve 3.3 V output:
tss = 100,000 * 1 uF * ln[(3.3 V + 5)/5] = 50.7 ms
Note that this is similar to the startup shown above as the TPS7A47xx EVM is configured for 3.3 V output with Cnr = 1 uF and Cout = 50 uF.
If you are not using ANY-OUT configuration:
tss = 100,000 * 1 uF * ln[(1.4 V + 5)/5] = 24.7 ms
The approximate startup delay (5 ms typical) can be subtracted from these results to calculate the rise time of the output.
Thanks,
Gerard Copeland
