Re: LPC2188 current?



I asked about current consumption specs for the LPC2888.

Robertus wrote:
I am not sure whether you are using the latest datasheet or the Users
Manual.
You can find the data sheet on the NXP website or here:
http://www.lpc2000.com/

The specification is there on page 28.

Thanks for pointing me at newer data on that site.

I downloaded both the datasheet and user manual from the NXP web site
a few days ago. The data sheet (LPC2880_LPC2888_2.pdf) is Rev. 02
dated 21 November 2006. The spec on page 26 is <tbd>.

It seems odd that lpc2000.com, which if I understand correctly is not
officially affiliated with NXP, has newer datasheets and user manuals
than the official NXP site!

In "stop mode", for which they give a typical Ibat spec of 17.7uA,
is the RAM kept alive? And can the GPIO interrupts wake it up from
that state?

What I'm concerned with is power dissipation in two specific states:

1) The product is "on", with something being displayed on an LCD module,
but with the CPU not running while waiting for the user to press any
button on a keypad.

2) The product is "off". Only a specific "ON" button needs to turn
it on.

Figure 10 shows a "start" switch connected to the START pin to turn
on the DC-DC converter. But when the power source is a single
alkaline cell, doesn't the DC-DC converter need to be on to keep the
internal SRAM alive? If so, I need a typical power spec for the
DC-DC converter(s) on but the CPU and all IO devices (other than GPIO)
halted. The closest thing I see to a spec for that is Idd with
32kHz active (which I don't need), 12MHz stopped, and DC-DC converter
supplying 1.8V. That spec is 200 uA, from which I assume that the
corresponding Ibat would be more than 400 uA at 0.9V (low end of
battery range). 400 uA drain in a powered off state is far too much
for a portable consumer device, and probably too much for the "on but
idle" state as well.

Or will the RAM be kept alive by the DCDC_Vbat pin, in which case the
17.7 uA typ Ibat spec is all I need to worry about? Except that if
I want to use that for the idle state, I need to contrive for any
button of the keypad to trip the START pin. Ugh. That would suggest
using a second low-power microcontroller just to handle the keypad.

Thanks!
Eric
.



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