AN2621 Application note TS488/9 low power stereo headphone amplifier evaluation board user guidelines Introduction This application note concerns the evaluation board DEMOTS488/9, designed to evaluate the TS488 or TS489 pop-free 120mW stereo headphone amplifier. In this document, you will find: ■ a brief description of the TS488/9 low power stereo audio amplifier ■ a description of the evaluation board and all of its components ■ the layout of the evaluation board About the TS488, TS489 The TS488/9 is an enhancement of TS486/487 that eliminates pop & click noise. It is a dual audio power amplifier capable of driving, in single-ended mode, either a 16Ω or a 32Ω stereo headset. It delivers up to 31mW per channel (into 16Ω loads) of continuous average power with 0.1% THD+N in the audio bandwidth from a 2.5V power supply. An externally-controlled standby mode reduces the supply current to 10nA (typical). The TS488/9 is unity gain stable and is configured by external gain-setting resistors. Key features of the TS488/9 include: ■ Pop & click noise protection circuitry ■ Operating range from VCC = 2.2V to 5.5V ■ Standby mode active low (TS488) or high (TS489) ■ Output power: – 120mW @5V, into 16Ω with 0.1% THD+N max (1kHz) – 55mW @3.3V, into 16Ω with 0.1% THD+N max (1kHz) ■ Low current consumption: 2.7mA max @5V ■ Ultra low standby current consumption: 10nA typical ■ High signal-to-noise ratio ■ High crosstalk immunity: 102dB (F = 1kHz) ■ PSRR: 70dB typ. (F = 1kHz), inputs grounded @5V ■ Unity-gain stable ■ Short-circuit protection circuitry ■ Available in lead-free MiniSO-8 and DFN8 2mm x 2mm For complete information about the TS488/9, refer to the datasheet. September 2007 Rev 1 1/5 www.st.com AN2621 1 Description of the evaluation board The DEMOTS488/9 is an evaluation board designed for the TS488/9 pop-free 120mW stereo headphone amplifier. The gain (AV) is set at 1 V/V for both channels and can be adapted if necessary with a modification of R11 or R12 values for channel 1, and of R21 or R22 values for channel 2. Table 1. Gain per channel Channel Gain (V/V) Channel 1 A V = – R12 ----------R11 Channel 2 R22 A V = – ----------R21 C11 with R11 (or C21 with R21) create an input high-pass filter with a cut-off frequency of 24.1Hz. C13 with a 16Ω load (or C23 with a 32Ω load) create an output high-pass filter with a cut-off frequency of 45.2Hz (22.6Hz). For information on how to change the value of the cut-off frequency, refer to the datasheet. The C12 and C22 component locations are left empty in order to add a low-pass filter if required. Table 2. Evaluation board connectors Connector Description P1 Power connector (VCC and GND). Power supply voltage from 2.2V to 5.5V P2 Standby control connector: – 1 2 3 pins 1 and 2 are shorted, TS488 operation mode, TS489 standby mode – 1 2 3 pins 2 and 3 are shorted, TS488 standby mode, TS489 operation mode The connector pins are as follows: – 1: VCC – 2: Standby control – 3: GND P10 Input signal connector (GND and active input signal). The pin 1 and 2 for the input 1 and the pin 3 and 4 for the input 2 P20 Output signal connector (GND and active output signal). The pin 1 and 2 for the output 1 and the pin 3 and 4 for the output 2 ` ` Caution: 2/5 When you apply the power supply through P1, do not invert the polarity because it would destroy the amplifier at U1. AN2621 Figure 1. Schematic diagram C12 P1 VCC 1 2 R12 20k Vcc Jumper J1 VCC C1 1uF VCC P2 C2 100nF 1 2 3 Vcc 8 U1 330nF 20k 2 C11 P10 R11 VOUT1 5 Input1 1 2 3 4 220uF VIN1 C3 3 Input2 R13 1k 1 OUT1 P20 C13 STDB 1 2 3 4 TS488=STDB BPS BIAS TS489=STDB 1uF 220uF Input 330nF 20k 6 VIN2 C23 GND R21 Output OUT2 7 R23 1k 4 C21 VOUT2 R22 20k C22 Table 3. Component list for the evaluation board Designation Quantity Description C11, C21 2 330nF/16V, ceramic capacitors, 0805 C12, C22 0 Not assembled, 0603 C2 1 100nF/16V, ceramic capacitors, 0805 C1, C3 2 1μF/50V, electrolytic capacitor, 1206 C13, C23 2 220μF/10V, electrolytic capacitor P1 1 2-pin header 2.54mm pitch P2 1 3-pin header 2.54mm pitch P10, P20 2 4-pin header 2.54mm pitch J1 1 Jumper, 2.54mm pitch U1 1 TS488 or TS489 3/5 AN2621 2 Evaluation board layout The following schematics show the layers and the top view of the evaluation board. Figure 2. PCB top layer Figure 4. Top view of evaluation board 3 Revision history Table 4. Document revision history 4/5 Date Revision 25-Sep-2007 1 Figure 3. PCB bottom layer Changes Initial release. AN2621 Please Read Carefully: Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries (“ST”) reserve the right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any time, without notice. All ST products are sold pursuant to ST’s terms and conditions of sale. Purchasers are solely responsible for the choice, selection and use of the ST products and services described herein, and ST assumes no liability whatsoever relating to the choice, selection or use of the ST products and services described herein. No license, express or implied, by estoppel or otherwise, to any intellectual property rights is granted under this document. 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