wm8350 Wolfson Microelectronics plc, wm8350 Datasheet - Page 158

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

WM8350
17.5 EXTERNAL INTERRUPTS
17.6 BACKUP POWER
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The power supply control circuit has a first-level interrupt, EXT_INT (see Section 24). This comprises
three second-level interrupts which indicate if the USB, Wall or Battery supplies have been
connected or disconnected. Internal feedback signals USB_FB, WALL_FB and BATT_FB are used
to indicate when the associated supplies are present. Note that these interrupt events occur on both
the rising and falling edges of the trigger events. They can be masked by setting the applicable mask
bits as defined in Table 102.
R31 (1Fh)
Comparator
Interrupt Status
R39 (27h)
Comparator
Interrupt Status
Mask
Table 102 External Interrupts
A backup power source should be provided for the WM8350 on the VRTC pin. This can be a small
rechargeable battery or a high-capacitance capacitor (supercap). The purpose of this component is
to power the always-on functions such as the on-chip crystal oscillator, RTC and ALARM control
registers and UVLO comparator. As these circuit blocks store settings required for start-up, it is
desirable that they continue to operate even when no other power source is available.
The VRTC battery (or capacitor) maintains its charge from the Wall (LINE), USB or BATT sources.
The connection is illustrated in Figure 75. The series resistor limits the VRTC charge current. The
1μF capacitor is recommended also for stability; if this capacitor is too small or is not present, the
VRTC output may oscillate and cause a system reset.
Figure 75 Backup Power
Note that, if the main battery is not present or is heavily discharged, and the WM8350 enters
BACKUP mode from Wall or USB power, then leakage may occur between VRTC and LINE. This will
cause the Backup Power source to be drained more quickly, and reduce the time for which the
WM8350 can maintain the RTC.
The leakage occurs via the switched-VRTC connection (SWVRTC) and the AUX1 pin; a resistor is
normally connected between these pins as part of the battery temperature detection circuit, as
ADDRESS
BATT
LINE
USB
Primary
power source
Secondary
power source
Third
power source
15:13
BIT
15
14
13
Regulator
EXT_USB_FB_EINT
EXT_WALL_FB_EINT
EXT_BATT_FB_EINT
“IM_” + name of respective bit
in R31
VRTC
WM8350
LABEL
Always-on
circuitry
VRTC
1 F
USB_FB changed interrupt.
(Rising and Falling Edge triggered)
Note: This bit is cleared once read.
WALL_FB changed interrupt.
(Rising and Falling Edge triggered)
Note: This bit is cleared once read.
BATT_FB changed interrupt.
(Rising and Falling Edge triggered)
Note: This bit is cleared once read.
Interrupt mask.
0 = Do not mask interrupt.
1 = Mask interrupt.
Each bit in R39 enables or masks the
corresponding bit in R31. The default
value for these bits is 0 (unmasked).
GND
DESCRIPTION
PD, June 2009, Rev 4.1
1k - 2.2k
Small battery
or super-cap
Production Data
158