LPC812 power consumption

[lpcware]

Content originally posted in LPCWare by Stefbert on Wed Mar 25 12:41:04 MST 2015
Hello,

I try to reproduce the messurement of the needed current of an LPC812 with the LPCXpresso LPC800 eval board. For that reason I cut all connections between the programming interface and the controller and connect only the signals SWDIOX, SWCLKX, GND and 3V3. An ampere meter is connect in the suppy wire.

Inside the datasheet of the device I found the following informations:
Conditions: Tamb = 25 °C; active mode entered executing code while(1){} from flash; all
peripherals disabled in the SYSAHBCLKCTRL register (SYSAHBCLKCTRL =0x1F); all peripheral
clocks disabled; internal pull-up resistors disabled; BOD disabled; low-current mode.
1 MHz - 6 MHz: IRC enabled; PLL disabled.
12 MHz: IRC enabled; PLL disabled.
24 MHz: IRC enabled; PLL enabled.
30 MHz: IRC disabled; SYSOSC enabled; PLL enabled.
Fig 14. Active mode: Typical supply current IDD versus supply voltage VDD

The figure shows the following currents:
24MHz approx. 2,1mA
12MHz approx. 1mA
6MHz approx.  700µA
2MHz approx.  500µA

My expectation is that I can reproduce this values. So I write a simple programm to verify this. The results I got are much higher than the given values.

So my question(s):
a) Did I missunderstand the datasheet an it is not possible to run the controller by 12MHz in active mode with a current near to 1mA ?
b) Can someone explain how to use the "low-current mode" ?

Thanks and best regards
Stef 

[lpcware]

Content originally posted in LPCWare by Stefbert on Thu Mar 26 12:35:15 MST 2015
Hi nerd herd,

I use an LPCXpresso LPC812 Rev A board. As descriped, I cutted the connection close to J4, mount pins and connect online power supply and debug-wires to the LPC. The pins normaly driving the LED are not powering the LED. My problem is that the current is not a little bit higher, its up to factor 3 higher, means that I measure a current of close to 3mA@12MHz, or 2mA@4MHz. This seams to make sence ... it is just a factor of 3 to high ...

Thanks and best regards from Germany
Stef

[lpcware]

Content originally posted in LPCWare by nerd herd on Thu Mar 26 10:55:09 MST 2015
Hi Stefbert,

You are right that the application note refers to low power mode current as opposed to the the active mode current. The reason I referred you to the AN is that the code and documentation should talk a little bit more about how to reduce overall power consumption (such as setting all unused pins as GPIOs as output high to reduce leakage current, turning off all peripheral clocks in SYSAHBCLKCTRL, turning off analog blocks in PDRUNCFG, etc.).

Regardless, what board are you using? Is it an eval board or a custom?

[lpcware]

Content originally posted in LPCWare by Stefbert on Wed Mar 25 23:20:30 MST 2015
Good morning,

I read inside the AN11561 and found some things that fits to the datasheet. AN11561: In "Sleep Mode" the needed current is approx. 700µA. The value is close to the value inside the diagram  (Fig. 16) in the datasheet. So the suggestion should bei right that datasheet figure 14 shows the processor in active mode, which means that no further low-power-function like sleep mode will be used.

So again my question do I unterstand something completly wrong ?

Thanks and  best regards
Stef

[lpcware]

Content originally posted in LPCWare by Stefbert on Wed Mar 25 14:14:57 MST 2015
Hello nerd herd,

thanks for your reply. It seems that I have a different expactation of the word "activ mode". I just thought it means that the cpu is still running ... hence be activ. The power modes descripes technics to enter low power modes, where the cpu stops working and will be wake up from interrupts. So is the real problem that I missunderstand the word "activ mode" in a wrong meaning ?

Thanks and best regards
Stef

[lpcware]

Content originally posted in LPCWare by nerd herd on Wed Mar 25 12:56:46 MST 2015
Hi Stefbert,

It is likely that you may not be fully turning everything off. Have you tried using the software in the low power application note?

http://www.lpcware.com/content/nxpfile/lpc800-low-power-modes-and-wake-times