Brown-out due to slow ramp-up time of Vdd?

[kaibecker]

Hi,

I have a question concerning the ramp-up time for Vdd in conjunction with the brown-out detection.

We are using an LPC1519 and the brown-out is configured to reset at 2,64V.

After a reset has occured, the reset source is checked. If the reset source was brown-out, an error is signaled on

the display.

That was tested and worked good.

Now we have new hardware revision. We used the same software, and suddenly the brown-out error was shown

on the display when connecting the device to the mains. We examind the Vdd with an oscilloscope. The voltage rises on both hardware versions without any dips or something. The only difference is the rise time or ramp-up time.

The old hardware had an adjustable voltage regulator and the Vdd went from 0V to ~3,22V in about 600µs.

The new hardware has an fixed voltage regulator. Vdd rises here from 0V to 3,3V in about 1,6ms.

I could not find anything in the datasheet or the user manual of the LPC1519, if this longer ramp-up time could cause

a brown-out reset or what maximum ramp-up time the LPC1519 needs.

Does anybody has similar experiences or can anyone confirm, that the slower ramp-up time for Vdd can cause

a brown-out reset?

If we would know, that this is the cause we could sleep better :-)

Kind regards

Kai

[xiangjun_rong]

Hi, Kai,

I suppose this is the procedure, at the low voltage which is less that the BOD threshold, the internal Reset is released, the code is running, your code enable the BOD, so the BOD interrupt is triggered.

I suggest you use a RC circuit to generate the Reset signal, you can use large resistor and large capacitor to enlarge the RC value so that you can enlarge the external /Reset signal deasserted time until the power supply voltage reaches up to 3.3V.

Hope it can help you

BR

XiangJun Rong