WM8352 datasheet(148/336 Pages) WOLFSON

148 / 336 page

WM8352

Production Data

PD, February 2011, Rev 4.4

148

16.2.2

PROGRAMMING THE SINK CURRENT

The sink currents for ISINKA and ISINKB can be independently programmed by writing to the

CS1_ISEL and CS2_ISEL register bits. The current steps are logarithmic to match the logarithmic

light sensitivity characteristic of the human eye. The step size is 1.5dB (i.e. the current doubles every

four steps).

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R172 (ACh)

Current Sink

Driver A

5:0

CS1_ISEL

00 0000

ISINKA current = 4.05μA × 2CSn_ISEL/4

where CS1_ISEL is an unsigned binary

number

Minimum: 00 0000 = 4.05μA,

Maximum: 11 1111 = 220mA

(from circuit simulation)

CS1_ISEL = 13.3 × log (desired current /

4.05μA)

R174 (AEh)

Current Sink

Driver B

5:0

CS2_ISEL

00 0000

ISINKB current = 4.05μA × 2CSn_ISEL/4

where CS2_ISEL is an unsigned binary

number

Minimum: 00 0000 = 4.05μA,

Maximum: 11 1111 = 220mA

(from circuit simulation)

CS2_ISEL = 13.3 × log (desired current /

4.05μA)

Table 97 Controlling the Sink Current for ISINKA and ISINKB

Note that currents above 40mA are not supported continuously; these settings are intended for flash

mode only.

16.2.3

FLASH MODE

Each current sink can either sink current continuously (LED mode) or in short bursts (flash mode).

The operating mode is selected by the CSn_FLASH_MODE bits, as described in Table 98.

In LED mode, the current sink is controlled by setting CSn_DRIVE. For as long as this bit is

asserted, the LED is enabled continuously.

In Flash mode, the current sink may be set to automatically flash every 4 seconds by setting

CSn_FLASH_RATE = 1, or may be triggered normally by setting CSn_FLASH_RATE = 0.

When normal triggering is selected in Flash mode, the trigger control can be either a GPIO Flash

input (see Section 20) or a register control. Setting CSn_TRIGSRC = 1 selects GPIO as the trigger.

The flash will be edge triggered by the selected GPIO input. Setting CSn_TRIGSRC = 0 selects the

this bit will be reset at the end of the flash.

In all flash modes, the duration of each flash is set by CSn_FLASH_DUR. The status of each current

sink may be read from the CSn_DRIVE bits.

In all modes, the current sink must also be enabled via the applicable CSn_ENA bit (see Table 96).

Note that some photo-flash applications may require a reservoir capacitor to store sufficient charge

for the flash.

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