Wiki > Main > SansaCharging (compare)
Difference: SansaCharging (r18 vs. r17)
This page describes the results of experiments on getting charging to work properly on Sansa players running Rockbox.
In the Sansa c200 and e200, charging is controlled by the AS3514 integrated circuit. It offers adjustable charge current (50 to 400 mA) and adjustable maximum charge voltage (3.90V to 4.25V). Charging is mostly automatic, the software just needs to configure charge current and maximum charge voltage and enable the charger. The charger has built-in safeties for voltage-too-low and temperature-too-low conditions. At the end of charging (when the charge current has dropped to about 10% of the configured charge current), the charger indicates end-of-charge and the software should disable the charger.
The charge status can be monitored through a set of status bits that indicate whether the charger is connected, enabled, done charging and if battery temperature is too high. The presence of a charger can also be detected through a separate GPIO pin. Various voltages related to charging can be monitored through the built-in ADC of the AS3514.
When monitoring the charge process, the interesting ADC voltages seem to be BVDD (the main battery voltage), RTCSUP (voltage of RTC battery?), CHGIN (charger input voltage) and BATTEMP (readout of thermistor inside battery, value decreases for higher temperature). In the early stages of charging, there is no significant change in the voltages, with the following typical values (charging on my laptop with 200 mA to 4.1V):
These voltages are way too high to be realistic as the true battery voltage. The OF does not indicate how full the battery already is during charging, which suggests that it may not be possible at all.
The CHGIN voltage turns out to depend on the configured charge current: a higher charge current shows a lower voltage. Also the CHGIN voltage starts to increase near the end of a charge cycle (charging in constant-voltage mode) when the charge current is falling. When the charger finally indicates end-of-charge and the software turns off the charger, the CHGIN voltage jumps up a little further.
The battery voltage during charging can not be read from the BVDD voltage as expected, it is way too high (like 4.550V). As an alternative it seems that the RTCSUP voltage works. During charging it stays at realistic values and saturates at the configured maximum charging voltage near the end of the charge. When not charging, the RTCSUP voltage is very close to BVDD.
The SansaView uses an AS3517 chip, which seems to be very similar to the AS3514 w.r.t. charging.
The AMS Sansa targets use an AS3525, which is very similar to the AS3514 used in the c200 and e200.
The following table summarises the battery properties and charge settings of the Sansa targets:
Other pages of interest:
r18 - 04 Mar 2010 - 13:48:38 - BertrikSikkenRevision r18 - 04 Mar 2010 - 13:48 - BertrikSikken
Revision r17 - 17 Jan 2010 - 14:21 - BertrikSikken
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