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Semtech has announced what it claims is the industry’s first smart current sink LED backlighting platform with on-chip digital lighting effects for high-end handheld displays.

This platform incorporates Semtech’s patent-pending smart Automatic Dropout Prevention (ADP) technology to enable a new generation of high-quality current sink drivers that can replace boost converters and charge pumps in high-end handhelds, while providing high-quality display backlighting.

The SC667 and SC668 current sinks with ADP technology reduce the total parts count and extend battery life compared with boost converters or charge pumps, offering high illumination quality.

Additionally, on-chip digital lighting effects provide the flexibility to incorporate fade, breathe and blink effects without changing the firmware.

White LEDs used in backlighting applications typically have a forward voltage up to 3.6V.

When the battery voltage declines in portable devices, the supply voltage must be boosted to ensure that the white LEDs have sufficient voltage to illuminate the display.

Charge pump or inductive boost converter devices have typically been used to provide this voltage boost function.

In an effort to maintain constant output power, these circuits increase current draw as the battery voltage declines, shortening battery life.

‘Semtech’s ADP technology ensures that the LEDs dim in uniform and imperceptible steps as the battery voltage declines,’ said said Athar Zaidi, director of marketing in Semtech’s Power Management Group.

Semtech’s smart ADP topology automatically and simultaneously monitors each current sink to avoid dropout as the system loads turn on and off.

Each time a current sink with ADP approaches dropout, the digital logic reduces the current setting for all of the backlight LEDs in small increments that are imperceptible to the human eye.

This process continues until all current sinks have sufficient headroom to regulate their current at the reduced setting.

When this point is reached, the ADP circuitry locks the current setting, eliminating any display flicker.

The SC667 and SC668 are the first current sinks to incorporate ADP technology.

These devices also integrate a number of functions to enable high-end features on portables, including an ambient light sensing/control circuit that sets backlight brightness based on surrounding lighting conditions.

A PWM dimming interface that incorporates a digital low-pass filter is also included, providing the capability to perform content-adaptive brightness control (versus ‘always-on’ illumination).

The SC668 provides eight current sinks, while the SC667 features seven current sinks plus an interrupt request indicator signal to tell the host processor when an ambient light threshold has been crossed.

Both devices include an on-chip digital lighting-effects engine to control LED fade-in/fade-out, breathe, blink, auto-dim full and auto-dim partial; an I 2C interface to program and control the LEDs; and four programmable, 200mA low-noise LDO regulators to manage the power for multiple embedded peripherals.

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