WM8352 datasheet(147/336 Pages) WOLFSON

147 / 336 page

Production Data

WM8352

PD, February 2011, Rev 4.4

147

16 CURRENT SINKS (LED DRIVERS)

16.1 GENERAL DESCRIPTION

The WM8352 includes five pins for driving different types of LEDs.

The pins ISINKA and ISINKB provide programmable constant-current sinks designed to drive strings

of serially connected LEDs, including white LEDs used in display backlights or in camera flash

applications. Using ISINKA and ISINKB in conjunction with DC-DC Converters 2 or 5 provides a

particularly power-efficient way to drive such LED strings. The ground connection associated with

these two Current Sinks is the SINKGND pin.

ISINKC, ISINKD and ISINKE are regular open-drain outputs. They are alternate functions of the

GPIO10, GPIO11 and GPIO12 pins respectively. These GPIOs are provided on the LINE power

domain; the associated ground connection is the GND pin.

16.2 CONSTANT-CURRENT SINKS

ISINKA and ISINKB are dedicated LED driver pins equipped with programmable constant current

sinks. They are designed to drive strings of serially connected white LEDs such as those used in

display backlights or photo-flash applications. Powering LEDs in this way is particularly power

efficient because no series resistor is required. DC-DC converters 2 or 5, operating as a current-

controlled voltage source, are ideal power sources for LED strings. These converters can generate

voltages higher than BATT or LINE, which can overcome the combined forward voltages of long LED

strings (e.g. a string of 7 white LEDs with a forward voltage of 4V requires at least 28V).

16.2.1

ENABLING THE SINK CURRENT

In Active mode, ISINKA and ISINKB can be enabled in software using the register fields defined in

Table 96. If required, the Current Sink functions may also be controlled by the Hibernate bit.

Note that these control bits do not exist for ISINKC, ISINKD or ISINKE.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R14 (0Eh)

Power mgmt

(7)

CS1_ENA

Current Sink 1 enable (ISINKA pin)

0 = disabled

1 = enabled

R172 (ACh)

Current Sink

Driver A

CS1_HIB_MO

Current Sink 1 behaviour in Hibernate

mode

0 = disable current sink in Hibernate

1 = leave current sink as in Active

R14 (0Eh)

Power mgmt

(7)

CS2_ENA

Current Sink 2 enable (ISINKB pin)

0 = disabled

1 = enabled

R174 (AEh)

Current Sink

Driver B

CS2_HIB_MO

Current Sink 2 behaviour in Hibernate

mode

0 = disable current sink in Hibernate

1 = leave current sink as in Active

Note: CS1_ENA and CS2_ENA can be accessed through R14 or through R172/R174. Reading from

or writing to either register location has the same effect.

Table 96 Enabling ISINKA and ISINKB

When ISINKA or ISINKB is used in conjunction with DC-DC Converter 2 or 5, the ISINK should

always be switched on before the DC-DC Converter is switched on. Conversely, the DC-DC

Converter should always be switched off before the ISINK is switched off. If high voltages are used,

additional external components may also be needed to protect the WM8352.

WM8352 Datasheet(PDF) 147 Page - Wolfson Microelectronics plc

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