WM8281ECSSLASHR datasheet(313/392 Pages) CIRRUS

313 / 392 page

WM8281

Rev 4.0

313

THERMAL SHUTDOWN AND SHORT CIRCUIT PROTECTION

The WM8281 incorporates thermal protection functions, and also provides short-circuit detection on

the Class D speaker and headphone output paths, as described below.

The temperature sensor detects when the device temperature is within normal limits or if the device is

approaching a hazardous temperature condition.

The temperature sensor is an input to the Interrupt control circuit and can be used to trigger an

Interrupt

event

see

“Interrupts”.

two-stage

indication

provided,

via

the

SPK_OVERHEAT_WARN_EINTn and SPK_OVERHEAT_EINTn interrupts.

If the upper temperature threshold (SPK_OVERHEAT_EINTn) is exceeded, then the Class D speaker

outputs will automatically be disabled in order to protect the device. When the speaker driver

shutdown is complete, a further interrupt, SPK_SHUTDOWN_EINTn, will be asserted.

The short circuit detection function for the Class D speaker outputs is triggered when the respective

output drivers are enabled (using the register bits described in Table 61). If a short circuit is detected

at this time, then the enable will be unsuccessful, and the respective output driver will not be enabled.

The Class D speaker short circuit detection provides inputs to the Interrupt control circuit and can be

used to trigger an Interrupt event - see

“Interrupts”.

If the Class D speaker short circuit condition is detected, then the respective driver(s) will

automatically be disabled in order to protect the device. When the speaker driver shutdown is

complete, a further interrupt, SPK_SHUTDOWN_EINTn, will be asserted.

To enable the Class D speaker outputs following a short circuit detection, the host processor must

disable and re-enable the output driver(s) twice over (ie. disable, enable, disable, enable). Note that

the short circuit status bits will always be cleared when the drivers are disabled.

The short circuit detection function for the headphone output paths operates continuously whilst the

respective output driver is enabled. If a short circuit is detected on any headphone output, then

current limiting is applied, in order to protect the output driver. Note that the respective output driver

will continue to operate, but the output is current-limited.

The short circuit detection function for the headphone outputs is designed to operate under a range of

typical load conditions. However, it is not compatible with highly reactive loads (either inductive or

capacitive), as found on some multi-driver headphones, due to phase shifting that arises under these

conditions. The headphone short circuit detection function must be disabled if these load conditions

may be applicable.

The short circuit detection function for the headphone output paths is enabled by default, but can be

disabled using the register bits described in Table 127. The output path performance (THD, THD+N)

is improved when the short circuit function is disabled.

Note that, when writing to the HPn_SC_ENA bits, care is required not to change the value of other

bits in the same register, which may have changed from the default

setting. Accordingly, a ‘read-

modify-

write’ sequence is required to implement this.

The headphone output short circuit detection provides inputs to the Interrupt control circuit and can be

used to trigger an Interrupt event - see

“Interrupts”. Note that two short circuit indications are

implemented for each headphone output channel (relating to detection in the positive and negative

output voltage regions respectively); if either of these indications is asserted, then a short circuit

condition exists in the respective output path.

WM8281ECS/R Datenblatt(PDF) 313 Page - Cirrus Logic

WM8281ECS/R Datenblatt(HTML) 313 Page - Cirrus Logic

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datenblatt Download

Link URL