Handset LED charge pump goes three ways

A new high-efficiency low-noise constant-frequency charge pump for white LED applications meets the demanding cost/performance standards of today's mass market consumer cellphones.

Meeting the demanding cost/performance standards of today's mass market consumer cellphones, leading developer of innovative power management solutions AnalogicTech has introduced a high-efficiency low-noise constant-frequency charge pump for white LED applications.

The three-channel trimode charge pump provides the right balance of functionality and silicon overhead to meet the commercial and functional standards that these highly competitive consumer applications require.

Integrating a 1x load switch, 1.5x fractional and 2x doubling charge pump, the AAT3142 is optimised for the unique backlight power requirements of high-volume consumer cellphones with small, efficient colour displays.

Trimode devices increase efficiency by stepping up voltage only when necessary.

As 80% of the discharge cycle of a lithium-ion/polymer battery is spent above the 3.5V threshold needed to drive white LEDs, constant use of a charge pump would waste energy.

By integrating a 1x load switch, trimode devices like the AAT3142 allow the battery voltage to pass through to the output when sufficient voltage is available.

The 1.5x and 2x charge pump modes are only activated when the battery power is low, allowing these devices to offer efficiency competitive to typical inductive boost convertors.

The AAT3142 produces 32 constant current levels up to 30mA for each output from a 2.7 to 5.5V input.

The device uses AnalogicTech's S2Cwire (Simple Serial Control) serial digital input to enable, disable, and set current for each LED.

To reduce parts count and system footprint in compact portable devices, the AAT3142 uses a 1MHz switching frequency which enables the use of highly compact, 1uF external capacitors: two charge pump flying capacitors, one input capacitor, and one charge pump output capacitor.

An integrated thermal management system protects the device if a short-circuit condition occurs at the output pin.

Soft-start circuitry prevents excessive inrush current during startup.

A low current shutdown feature reduces quiescent current to less than 1uA.

Specified over the -40 to +85C temperature range, the AAT3142 is available immediately in a Pb-free, 12-pin TSOPJW package.

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