This page describes the results of experiments on getting charging to work properly on Sansa players running Rockbox.
AS3514 charger (c200 and e200)
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.
c200 charging and monitoring
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):
- BVDD: 4.610 V
- RTCSUP: 4.540 V
- CHGIN: 4.825 V
- BATTEMP: 0.868 V
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.
e200 charging and monitoring
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.
- when the charger cable becomes connected, the charger status shows some spurious status. The solution is to ignore the status while the charger still indicates it is unconnected.
- when the charger has never been turned off, it may fail to indicate end-of-charge (the hardware voltage/current limits are still effective, so this is probably not dangerous). The solution is to explicitly turn off the charger first before configuring it.
- the charger may indicate an end-of-charge directly after configuring it. The solution is to ignore the first charger status reading.
AS3517 charger (Sansa View)
uses an AS3517 chip, which seems to be very similar to the AS3514 w.r.t. charging.
AS3525 charger (AMS Sansas)
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:
|| charger HW
|| OF charge settings
|| battery capacity
|| ADC channel
|| I=300mA, V=4.25V
|| 530 mAh
|| BVDD indicates too high voltage during charge
|| I=300mA, V=4.25V
|| 750 mAh
|| BVDD indicates too high voltage during charge, RTCSUP seems OK
|| 730 mAh
|| I=100mA, V=4.20V
|| 350 mAh
|| I=?, V=4.20V
|| 730 mAh
|| Rockbox charges at 300 mA
|| I=200mA, V=?
|| 550 mAh
|| Rockbox charges at 200 mA, 4.20V
- "ADC channel" indicates what ADC channel represents the battery voltage best
Other pages of interest:
Copyright © by the contributing authors.