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Maximum capacitance EP5368QI and EP5388QI

I wonder why the maximum allowed capacitance on the EP5388QI (800 mA) is much lower than for the EP5368QI (600 mA) devices. The specifications regarding the dV/dt in VID mode are similar and even taking into account the much higher current limit for the latter, doesn't explain why it is so much lower.

We have been using the EP5368QI since 2011. Recently we're seeing products failing to startup due to apparent over-current problems, so we're in the process of changing to the EP5388QI.

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Hello Arjen, We updated EP5388QI datasheet to reflect the effect of the OCP limit to avoid the excessive output capacitance that will trigger the OCP during the startup. Regarding EP5368QI; we already in process to update the datasheet to follow the same concept like EP5388QI. So you can use the same equation with EP5368QI to calculate the allowed output capacitance. Regards, Mostafa
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In that case, what Imax current should I use for the OCP in the equation? For the EP5388QI the typical OCP limit is 1000 mA, while for the (lower rated) EP5368QI it is 2 A. That's fairly counter-intuitive: a more or less similar device with a lower output current rating has a higher PFET OCP level. Are these devices internally really that different?

 

I'm asking, because we're currently in the process of swapping out an EP5368QI for an EP5388QI due to over-current problems we're running into. The same circuit has worked flawlessly since 2011, but starting about a year ago, we're seeing unacceptable numbers of modules failing at -40°C, mostly in applications where it has to supply in the order of 500 mA @ 1.8 V (we use VID voltage setting in that application). Has something changed here?

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Hello Arjen,

Both EP5368 and EP5388 will have the same max capacitance where they are internally are almost the same.

Regards,

Mostafa

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This doesn't answer my question at all. According to the datasheets, the maximum allowed capacitance is vastly different. Now you're telling me it is the same. In that case, which one is the correct one?

 

Given the amount of problems we're seeing, I'd assume that the maximum capacitance of 700 uF in the specifications of the EP5368QI is too high. At temperatures below -30°C we've seen boards failing to startup with as little as 75 uF. We've dropped the amount of capacitance to 50 uF which seems to do the job, but this is way below the expected value.

 

If we change to the EP5388QI in this application, what can we expect?

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Hello Arjen,

I am so sorry if this doesn't answer you, but as i mentioned in my first response that EP5368's datasheet is under update process and it will have the same equation as EP5388.

COUT_MAX = 0.7 * (ILIMIT - IOUT) * tSS / VOUT

COUT_MAX = maximum allowable output capacitance

ILIMIT = minimum current limit = 0.8A

IOUT = output current at startup

VOUT = output voltage

0.7 = margin factor

tSS(VFB) = min soft-start time

= 0.784ms for External feedback setting

tSS(VID) = VOUT [V] / 2.025 [V/ms] for VID setting

 

So if you replace EP5368 with EP5388, you will have the same capacitance limit 50uF.

 

I will push Enpirion Team to release that update ASAP.

 

Regards,

Mostafa

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