Clarification of LPC82x power-up ramp wait time erratum

[duaneallen]

A new errata document has been published for the LPC82x (ES_LPC82x Rev 1.3). Section 3.5 VDD.1 of that document states:

Introduction:
On the LPC82x, the VDD supply voltage range is from 1.8 V to 3.6 V. The LPC82x
datasheet specifies a power-up ramp condition for the user application. Before ramping
up, the minimum wait time (twait) of the power supply on the VDD pin (200 mV or below) is
12 us.
Problem:
The device might not always start-up if the minimum wait time (twait) is 12 us. The required
minimum time (twait) specification is 2 ms.

It is unclear as to what this actually means, and what if any measures need to be taken to ensure proper startup of the microcontroller; reviewing the part's datasheet did not contribute anything that aided in understanding of the wait time requirement. Could someone provide a clearer and more detailed explanation of this, please?

Thanks!

[EngHuiPeng]

Hello Victor

Following is a question from customer(Schneider) : 

If the Vcc of MCU drops to a level >200mV (e.g: 201MV, 250mV, ….) before touching <=200mV, is the condition in the Errata apply? (ie. apply to Vdd >1.8V)

Appreciate your advice. 

Regards,

Audrey

[victorjimenez]

Hello, 

In the page 51 of the datasheet Figure 31 shows the graphic of the Power-up ramp. The wait time (twait) specifies the time the power supply must be at levels below 200mV. In the datasheet says that this time has to be at least 12us before the ramping. However, the errata says that the device won't start always if you only wait 12us, in order to avoid that is better wait 2ms before the ramping. 

These power up conditions must be met when you do a power-on reset. You can check this by connecting a oscilloscope to VDD and make a power-on reset on the LPC, this way you should see the same response as in Figure 31 as shown in the attach image

This could only affect you if you are making continuous power on resets.

Hope it helps!

Victor.

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