ST AN2621 Application note
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 |
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Channel |
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Gain (V/V) |
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Channel 1 |
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AV |
= |
R12 |
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–---------- |
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R11 |
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Channel 2 |
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AV |
= |
R22 |
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–---------- |
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R21 |
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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 |
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Standby control connector: |
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– |
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pins 1 and 2 are shorted, TS488 operation mode, TS489 standby mode |
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1 |
2 |
3 |
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– |
1 |
2 |
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3 |
pins 2 and 3 are shorted, TS488 standby mode, TS489 operation mode |
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P2 |
The connector pins are as follows: |
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–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: When you apply the power supply through P1, do not invert the polarity because it would destroy the amplifier at U1.
2/5
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