Class-D audio amps and current limiting switches target portable, consumer apps

At Electronica in Munich, Germany, ON Semiconductor (Hall A5, Stand 225) is introducing four new devices designed to support portable and consumer electronics applications.

ON Semiconductor is offering a range of power management, protection, audio and video solutions for portable and consumer applications. With an emphasis on integration, low power and high efficiency in low profile, small footprint packages, ON Semiconductor is able to support the needs of both current and future generation portable and consumer products such as smart phones, personal media players, digital cameras, LCD televisions, set-top-box and DVD players.

The NCP2704 audio subsystem IC and the NCP2824 low noise Class D amplifier represent the latest audio offerings from ON Semiconductor. The two devices give designers high efficiency and space saving solutions for their portable power amplifier requirements.

The NCP2824 is a low Electro-Magnetic Interference (EMI) Class D amplifier with Auto Gain Control (AGC), and power limiter functions. The NCP2704 is a subsystem that integrates the same low noise Class D amplifier with a low power headphone amplifier which helps to extend battery life thus enabling longer audio playback time. Both devices deliver overall efficiency levels of approximately 90 percent and are designed to cover the audio power requirements of a wide variety of portable electronic devices such as cell phones, mobile Internet browsing devices and hands-free car kits.

A non-clipping function featured on both devices automatically reduces the amplifier's gain in order to limit the distortion when an excessive signal is applied to the input. This adjustment is enabled by the Automatic Gain Control (AGC) circuit that is built into the chip. The power limiter function limits the output power of the amplifier to protect speakers from damage caused by an excessive sound level. Both AGC functions are adjustable.

The NCP2824 employs a single-wire interface to simplify designs. The NCP2704 meanwhile, offers extensive control through an I²C protocol for adapting the AGC, signal multiplexing and the EMI reduction level to meet system requirements.

ON Semiconductor's new NCP380 and NCP382 are respectively single input / single output and single input / dual output, current limiting distribution switches designed for use in USB ports where heavy capacitive loads and short-circuits are likely to be encountered. Typical end applications include laptop/desktop computers, hubs, set top boxes, televisions and gaming products. The new devices limit output current to a desired level by switching into a constant-current mode when the output load exceeds the current-limit threshold or a short is present. The power switches' rise and fall times are controlled to minimise current ringing during switching. More critically, short detection times allow huge inrush currents to be limited.

The NCP382 incorporates two 80 mO MOSFETs, is available in either DFN8 3 mm x 3 mm or SOIC-8 packages and has a current limit threshold that is internally fixed at 500 milliamps (mA), 1000 mA or 1500 mA. The NCP380 meanwhile incorporates a single 70 mO MOSFET and is offered in a choice of UDFN6, TSOP-5, or TSOP-6 packages. Current limit threshold is again fixed at 500 mA, 1000 mA or 1500 mA or is user adjustable via an external resistor between 100 mA and 1.5 A.

The NCP380 and NCP382 have a 2.5 V to 5.5 V operating voltage range and include features such as soft-start, soft turn-off, thermal protection, and reverse voltage protection. Both devices are compliant with IEC61000-4-2 (level 4) and have a junction operating temperature range of -40 to +125 degrees C.

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