wm8351 Wolfson Microelectronics plc, wm8351 Datasheet - Page 152

• Manufacturer Part Number: wm8351
• Description: Wolfson Audioplus? Stereo Codec With Power Management
• Manufacturer: Wolfson Microelectronics plc

WM8351
17.2 BATTERY POWERED OPERATION
17.3 WALL ADAPTOR (LINE) POWERED OPERATION
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HIVDD is an external connection which exists for the purposes of decoupling only. It represents the
highest available power supply connected to the WM8351. It should be noted that the preferred
supply (on the LINE pin) is not necessarily the same voltage as HIVDD - the Wall supply will always
be the preferred voltage when it is within the intended limits, even if it is not also the highest available
source.
The main battery connects directly to the BATT pin. When the battery is the preferred supply source,
this pin is an input. When battery charging is in operation, this pin is an output. (Note that the backup
VRTC battery is connected separately - see Section 17.5.)
The USB interface connects directly to the USB pin. In USB Master Mode (USB is less than LINE),
the WM8351 can supply power to external devices on this pin. In USB Slave Mode (USB is greater
than LINE), the WM8351 can use this pin as an input to power the device and/or to charge a battery
connected to the BATT pin. Note that, when USB is the preferred power supply, the Battery may also
be used if necessary to supplement the current drawn from the USB pin (ie. to source current into
LINE when required).
All loads connected to the WM8351 should normally be connected to the LINE pin. The inputs to the
DC-DC Converters and LDOs should be connected to the LINE pin. It is not recommended to
connect any load directly to the battery (BATT).
Note that the inputs to the LDOs may be connected to the outputs of the DC-DCs if desired.
The WM8351 selects battery power when the Battery voltage is higher than the Wall (LINE) and USB
supplies. In practical usage, this means the Battery is used when Wall (LINE) and USB are both
disconnected.
The battery can also be used to supplement the USB supply when required (ie. to source current into
LINE).
If the Wall (LINE) or USB supply becomes available during battery operation, then the selected
power source is adjusted accordingly.
Battery pack temperature sensing is enabled by default. The battery’s NTC resistor is monitored via
the AUX1 pin on the WM8351, as described in Section 17.7. Note that the absence of this NTC
connection will lead to a temperature failure condition being detected and battery charging will not be
possible.
Safe operation of the battery charger outside the designed operating temperatures is not guaranteed
when a battery NTC resistor is not used. The designed operating temperatures are noted in
Section 17.7.7.
The WM8351 selects Wall Adaptor power via the LINE pins whenever the Wall Adaptor supply is
within the normal operating limits of 4.0V to 5.5V. The Wall Adaptor is also selected as the power
source below 4.0V in the case where it is the highest available power source. The minimum LINE
voltage is a programmable threshold in the range 2.9V to 3.6V (see Section 18). The maximum
recommended operating voltage for LINE is 5.5V.
Note that USB power is not used when a suitable LINE supply is available, even if the USB supply is
higher than the Wall (LINE) supply.
If the Wall (LINE) supply becomes unsuitable and a USB is available, then the USB supply will be
selected as the preferred power source. Note that, when hot-swapping from Wall (LINE) to USB
supply, a usable Battery must be present on the BATT pin.
When the Wall (LINE) supply is selected and a Battery is connected, then trickle charging is enabled
by default, including when the WM8351 is in the OFF or HIBERNATE states. When the WM8351 is
in the ACTIVE state, then fast charging may be selected under software control.
PD, June 2009, Rev 4.1
Production Data
152