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MAX97220A Datasheet(PDF) 12 Page - Maxim Integrated Products |
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MAX97220A Datasheet(HTML) 12 Page - Maxim Integrated Products |
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12 / 19 page  12 Maxim Integrated Differential Input DirectDrive Line Drivers/Headphone Amplifiers MAX97220A–MAX97220E Detailed Description The MAX97220_ is a fully differential input line driver/ headphone amplifier for set-top boxes, LCD TV, and home theater applications where audio fidelity is of pri- mary importance. Power consumption of the amplifier is reduced while maintaining high SNR and THD+N per- formance. The MAX97220A/MAX97220B/MAX97220E require external input and feedback resistors to set amplifier gain. The MAX97220C/MAX97220D feature internal input and feedback resistors for a set gain of +6dB. Output swings of 3VRMS with a 5V supply and 2VRMS with a 3.3V supply are perfect for line driver applications. High fidelity is maintained through the differential input connection. An output noise voltage of 7FVRMS allows for 112dB SNR when powered from 5V and 109dB SNR when powered from 3.3V. The IC has better than 90dB THD+N across the entire audio bandwidth. The MAX97220_ operates from a single supply ranging from 2.5V to 5.5V. An on-chip charge pump inverts the positive supply (PVDD), creating an equal magnitude negative supply (PVSS). The headphone amplifiers operate from bipolar supplies with their outputs biased about PGND (Figure 1). The benefit of this PGND bias is that the amplifier outputs do not have a DC component, typically PVDD/2. The large DC-blocking capacitors required with conventional headphone amplifiers are unnecessary, thus conserving board space, reducing system cost, and improving frequency response. Output power of 125mW into 32I is achievable from a 5V sup- ply. The device features an undervoltage lockout that prevents operation from an insufficient power supply and click-and-pop suppression that eliminates audible transients on startup and shutdown. Differential Input The IC can be configured as differential or pseudo- differential input amplifiers (Figures 2 and 3), making it compatible with all codecs. A differential input offers improved noise immunity over a single-ended input. In devices such as cellular phones, high-frequency signals from the RF transmitter can couple into the amplifier’s input traces. The signals appear at the amplifier’s inputs as common-mode noise. A differential input amplifier amplifies the difference of the two inputs while signals common to both inputs are cancelled. Configured dif- ferentially, the gain of the MAX97220A/MAX97220B/ MAX97220E is set by: AV = RF/RIN The common-mode rejection ratio (CMRR) is limited by the external resistor matching, and if used, input capaci- tor matching at low frequencies. For example, the worst- case variation of 1% tolerant resistors results in 40dB CMRR, while 0.1% resistors result in 60dB CMRR. For best matching, use resistor arrays. Figure 1. Conventional Driver Output Waveform vs. MAX97220_ Output Waveform Figure 2. Differential Input Configuration VOUT PVDD PVDD/2 PGND PGND VOUT +PVDD -PVDD DirectDrive BIASING SCHEME CONVENTIONAL DRIVER-BIASING SCHEME OUT RF1* RIN1* IN- IN+ RIN2 RIN1 = RIN2, RF1 = RF2 *RIN1 AND RF1 ARE INTERNAL FOR MAX97220C/MAX97220D RF2 |
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