ON Semiconductor has introduced the NCS8353 stereo audio amplifier, a Class D device with efficiency levels of more than 87%, that eliminates the need for the inclusion of a heatsink in the system design, claims the company.
Aimed at the flat panel TV market the amplifier can be powered from the existing 24V backlight rail in the TV system and can deliver a continuous output power of up to 20W/channel into an 8Ω BTL (bridge tied load). The PWM technique utilised within the Class-D architecture permits filter-less operation in certain circumstances by using the speakers themselves as an LC filter.
Four selectable gain ranges are supported such as 20, 26, 32, and 36dB. An integrated digital power limiter can be set, using two external bits, to deliver a specific output of 10, 12, 15, or 20W. This protects the TV speakers from high amplitude input spikes, says the company. A shutdown function reduces the quiescent current drawn by the amplifier to 100µA, while the mute feature ensures that audio is not present at the output during audio source switching.
In order to permit uninterruptable audio operation at low output powers, the internal temperature should rise above the junction threshold of 150°C, the internal gain of the device is slowly reduced, claims the company. The combination of gain reduction and internal power dissipation results in a stable maximum junction temperature of approximately 140°C. The output stage will shut down if the junction temperature rises above 160°C. The power stage is re-enabled once the amplifier junction temperature cools to below 130°C.
If a short circuit event is detected, the output stage of the amplifier is completely disabled and an internal counter is activated. After a 100ms period the output stage will attempt to reactivate, with the cycle continuing until the short is removed. The amplifier is available in a 5x5mm, lead-free, 32pin QFN package.
