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MAX9705 Datasheet(PDF) 9 Page - Maxim Integrated Products |
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MAX9705 Datasheet(HTML) 9 Page - Maxim Integrated Products |
9 / 18 page 2.3W, Ultra-Low-EMI, Filterless, Class D Audio Amplifier _______________________________________________________________________________________ 9 Detailed Description The MAX9705 ultra-low-EMI, filterless, Class D audio power amplifier features several improvements to switch- mode amplifier technology. The MAX9705 features output driver active emissions limiting circuitry to reduce EMI. Zero dead time technology maintains state-of-the-art effi- ciency and THD+N performance by allowing the output FETs to switch simultaneously without cross-conduction. A unique filterless modulation scheme, synchronizable switching frequency, and spread-spectrum mode create a compact, flexible, low-noise, efficient audio power amplifier while occupying minimal board space. The dif- ferential input architecture reduces common-mode noise pickup with or without the use of input-coupling capaci- tors. The MAX9705 can also be configured as a single- ended input amplifier without performance degradation. Thermal-overload and short-circuit protection prevent the MAX9705 from being damaged during a fault condition. The amplifier is disabled if the die temperature reaches +125°C. The die must cool by 10°C before normal opera- tion can continue. The output of the MAX9705 shuts down if the output current reaches approximately 2A. Each out- put FET has its own short-circuit protection. This protec- tion scheme allows the amplifier to survive shorts to either supply rail. After a thermal overload or short circuit, the device remains disabled for a minimum of 50µs before attempting to return to normal operation. The amplifier will shut down immediately and wait another 50µs before turn- ing on if the fault condition is still present. This operation will cause the output to pulse during a persistent fault. Comparators monitor the MAX9705 inputs and com- pare the complementary input voltages to the sawtooth waveform. The comparators trip when the input magni- tude of the sawtooth exceeds their corresponding input voltage. Both comparators reset at a fixed time after the rising edge of the second comparator trip point, gener- ating a minimum-width pulse tON(MIN) at the output of the second comparator (Figure 1). As the input voltage increases or decreases, the duration of the pulse at one output increases (the first comparator to trip), while the other output pulse duration remains at tON(MIN). This causes the net voltage across the speaker (VOUT+ - VOUT-) to change. Operating Modes Fixed-Frequency Modulation (FFM) Mode The FFM mode is selected by setting SYNC = GND for a 1.1MHz switching frequency. In FFM mode, the frequen- cy spectrum of the Class D output consists of the funda- mental switching frequency and its associated harmonics (see the Wideband Output Spectrum Fixed- Frequency Mode graph in the Typical Operating Characteristics). Pin Description PIN BUMP TDFN UCSP NAME FUNCTION 1A1 VDD Analog Power Supply 2 B1 IN+ Noninverting Audio Input 3 C1 IN- Inverting Audio Input 4 C2 GND Analog Ground 5B2 SHDN Active-Low Shutdown Input. Connect to VDD for normal operation. 6 A3 SYNC Frequency Select and External Clock Input. SYNC = GND: Fixed-frequency mode with fS = 1100kHz. SYNC = VDD: Spread-spectrum mode with fS = 1220kHz ±120kHz. SYNC = Clocked: Fixed-frequency mode with fS = external clock frequency. 7 B3 PGND Power Ground 8 A4 OUT+ Amplifier-Output Positive Phase 9 C4 OUT- Amplifier-Output Negative Phase 10 B4 PVDD H-Bridge Power Supply —— EP Exposed Pad. Internally connected to ground. Connect to a large ground plane to maximize thermal performance. Not intended as an electrical connection point (TDFN only). |
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Similar Description - MAX9705_09 |
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