[Gta04-owner] Battery life on GTA04 ?

Dr. H. Nikolaus Schaller hns at goldelico.com
Fri May 20 14:00:25 CEST 2011

Hi Niklas,

Am 20.05.2011 um 06:54 schrieb tango at riseup.net:

> Hallo,
> nowadays one of the really annoying and limiting Freerunner issues is
> the battery. I hardly manage an average working day with some NeronGPS
> routing on QTMoko, happy to reach the charger before it starts running
> on low (battery is 6 month old).
> What about battery/energy saving on GTA4 ? Are the new components even
> more thirsty ? Are there new spare batteries planned with more
> capacity ?

Let me try to answer as good as possible, since some aspects have 
not been studied intensively enough.

The battery is the same as for the Freerunner, i.e. the FIC HF08x with 3.7V
and 1200mAh. The reason is that the new GTA04 board must fit
into the GTA02 case which defines the battery. There may be compatible
batteries with more capacity.

Next is about compontents being more thirsty. Generally, the highers
demand is an active GSM/UMTS transmitter. This may draw up to approx.
2 Amperes. But only in bursts and heavily depending on the power
control that is negotiated between the mobile and the base station.

So the typical power demand is much lower.

Another thirsty component is the WLAN module. This is specified for
max. 240mA @ 3.3V.

From experiments we also know that the SoC can draw a lot of power,
if all components are enabled. If we disable the DSP and the 3G accelerator,
and reduce the CPU clock we have measured that the operating current
has a variance between 90 and 450 mA. The DM3730 is better in general
power demand, but can be operated at 800 MHz which may need
the maximum current. Well, it may even be possible to overclock
the chip :)

Another major power demand comes from the LCD backlight. This
is operated by a step-up converter to provide 23 mA @ 13.5 V i.e.
310 mW. This is directly driven by the nominal battery voltage of
3.7V, i.e. assuming 90% efficiency this means the backlight draws
95 mA. So we may come to 300 mA (4h) without WLAN, 400 mA (3h)
with WLAN, 600 mA (2h) with UMTS being permanently active.

This is if all components are in active operation.

Power management functions that largely depend on the kernel using
them can reduce this by shutting down parts of the SoC until they are
really needed.

Now, what about standby? All components can be sent to standby mode
or have an active current below 1 mA. In this state, the CPU is off and just
refreshing some internal memory, the backlight is completely off, some
LEDs are pulsing for 10ms every 5 seconds. And, the UMTS modem is
passively waiting for receiving an incoming call to wake up the CPU.

This means the system can stay active and we expect that it draws below
10 mA. This would translate into 120 hours until the battery is down. 

But what we don't know yet, is the real active standby current required
by the UMTS modem.

So the main factor driving the standby time is the sleep mode of the
UMTS/GSM modem. On the Freerunner there was a hardware bug
(#1024) that prevented the modem to enter this low power standby mode.
After it was fixed, 130 hours have been reported. So I would expect the
GTA04 be in the same range.

We hope to find out these facts through the early adopter boards that
are currently starting to be produced.

-- Nikolaus

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