wm8350 Wolfson Microelectronics plc, wm8350 Datasheet - Page 159

• Manufacturer Part Number: wm8350
• Description: Wolfson Audioplus? Stereo Codec With Power Management
• Manufacturer: Wolfson Microelectronics plc

Production Data
17.7 BATTERY CHARGER
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illustrated in Section 17.7.1. The leakage does not occur if the WM8350 enters BACKUP mode from
Battery power, because the switched-VRTC output is not enabled in this case.
If no main battery is present in the system, then the SWVRTC pin should be left floating; this will
prevent any leakage in BACKUP mode.
If the application supports the connection of a main battery, then it is important to select a battery
pack where the NTC resistance is around 100kΩ at 25ºC. This will limit the leakage current to a
maximum of 23μA in BACKUP mode. Battery packs with lower NTC resistance are not
recommended as the leakage current in BACKUP will be higher.
If no backup battery is present in the system, then the leakage current is of no importance, as the
BACKUP state is not supported.
17.7.1
The WM8350 incorporates a battery charger which is designed for single-cell lithium batteries. The
battery charger can operate from either the Wall (LINE) or USB power sources. Trickle charging at
50mA is enabled by default. The battery charger configuration and termination can run without any
intervention required by the host processor.
The battery charger voltage and currents are programmable. Trickle charging at either 50mA or
100mA is supported; fast charging from 50mA up to 750mA is possible under certain conditions.
Note that charging from the USB power is subject to the 100mA or 500mA overall limit on the USB
source (see Section 17.4).
Battery pack temperature sensing is enabled by default. The connection to the battery’s NTC resistor
is made using the SWVRTC pin and the AUX1 pin, as illustrated in Figure 76. The SWVRTC pin is a
reference source controlled by the WM8350. The AUX1 pin (also an input to the AUXADC) is used as
the input to the temperature sensing circuit. Note that the absence of the NTC connection will lead to
a temperature failure condition being detected and battery charging will not be possible.
Typical connections for the WM8350 battery charger are illustrated in Figure 76. The resistor value
between SWVRTC and AUX1 should be selected to match the NTC. A typical value is 100kΩ.
Figure 76 Typical Connections for WM8350 Battery Charger
GENERAL DESCRIPTION
PD, June 2009, Rev 4.1
WM8350
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