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 elimina tes pop & click noise. It is a dual
audio power amplifier capa ble o f driving, in single-ended m ode, eit her a 16Ω or a 32Ω stereo
headset.
It delivers up to 31mW per channel (into 16 Ω loads) of continuous average power with 0.1%
THD+N in the audio bandwidth from a 2.5V power supp ly.
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.
Ke y features of the TS488/9 include:
■ Pop & click noise protection circuitry
■ Operating range from V
■ Standby mode active low (TS488) or high (TS489)
■ Output power:
= 2.2V to 5.5V
CC
– 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
1 Description of the evaluation board
The DEMOTS488/9 is an evaluation board designed for the TS488/9 pop-free 120mW
stereo headphone amplifier.
AN2621
The gain (A
) is set at 1 V/V for both channels and can be adapted if necessary with a
V
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
Channel 2
A
A
R12
---------- -–=
V
R11
R22
---------- -–=
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 loa d (or C23 with a 32 Ω load) create an output high-pass filter with a cu t-of f
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
P2
P10
P20
Pow er connector (V
Standby control connector:
`
– pins 1 and 2 are shorted, TS488 operation mode, TS489 standby mode
123
`
– pins 2 and 3 are shorted, TS488 standby mode, TS489 operation mode
123
The connector pins are as follows:
–1: V
CC
– 2: Standby control
–3: GND
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
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
and GND). Power supply voltage from 2.2V to 5.5V
CC
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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