WM8352 datasheet(156/336 Pages) WOLFSON

156 / 336 page

WM8352

Production Data

PD, February 2011, Rev 4.4

156

17.5 EXTERNAL INTERRUPTS

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 103.

ADDRESS

BIT

LABEL

DESCRIPTION

R31 (1Fh)

Comparator

Interrupt Status

EXT_USB_FB_EINT

USB_FB changed interrupt.

(Rising and Falling Edge triggered)

Note: This bit is cleared once read.

EXT_WALL_FB_EINT

WALL_FB changed interrupt.

(Rising and Falling Edge triggered)

Note: This bit is cleared once read.

EXT_BATT_FB_EINT

BATT_FB changed interrupt.

(Rising and Falling Edge triggered)

Note: This bit is cleared once read.

R39 (27h)

Comparator

Interrupt Status

Mask

15:13

“IM_” + name of respective bit

in R31

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).

Table 103 External Interrupts

17.6 BACKUP POWER

A backup power source should be provided for the WM8352 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

μF 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

WM8352 Datasheet(PDF) 156 Page - Wolfson Microelectronics plc

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