ST AN2622 Application note
AN2622
Application note
TS4909 low power stereo headphone amplifier
evaluation board user guidelines
Introduction
This application note concerns the DEMOTS4909 evaluation board, designed to evaluate
the TS4909 low power stereo headphone amplifier with capacitor-less output.
In this document, you will find:
■ a brief description of the TS4909 audio amplifier
■ a description of the evaluation board and all of its components
■ the layout of the evaluation board
About the TS4909
The TS4909 is a stereo audio amplifier designed to drive headphones in portable
applications.
The integrated phantom ground is a circuit topology that eliminates the heavy output
coupling capacitors. This is of primary importance in portable applications where space
constraints are v e ry high. A single-end ed conf igu r at ion is a lso available , o ffering ev en lower
power consumption because the phantom ground can be switched off.
Specially designed for applications requiring low power supplies, the TS4909 is capable of
delivering 52mW of continuous average power into a 32Ω load with less than 1% THD+N
from a 3V power supply. Pop & click noise during switch-on and switch-off phases is
eliminated thanks to integrated circuitry.
Ke y features of the TS4909 include:
■ No output coupling capacitors necessary
■ Pop & click noise reduction circuitry
■ Operating from V
■ Standby mode active low
■ Output power:
= 2.2V to 5.5V
CC
– 158mW @5V, into 16Ω with 1% THD+N max (1kHz)
– 52mW @3.0V into 32Ω with 1% THD+N max (1kHz)
■ Ultra low current consumption: 2.0mA typ.@3V
■ Ultra low standby consumption: 10nA typ.
■ High signal-to-noise ratio 105dB typ. @5V
■ High crosstalk immunity: 110dB (F=1kHz)
■ PSRR: 72dB (F=1kHz), inputs grounded
■ Low t
■ Available in lead-free DFN10 3x3mm
: 50ms in PHG mode, 100ms in SE mode
WU
For complete information about the TS4909, refer to the datasheet.
September 2007 Rev 1 1/5
www.st.com
Description of the evaluation board AN2622
1 Description of the evaluation board
The DEMOTS4909 evaluation board is designed for the TS4909 low power stereo
headphone amplifier with capacitor-less output.
The gain (A
) is set at 1 V/V for both channels and can be adapted if necessary with a
V
modification of R1 or R2 values for the Left channel, and R3 or R4 values for the Right
channel.
Table 1. Gain per channel
Channel Gain (V/V)
Left
Right
A
A
R2
------- -–=
V
R1
R4
------- -–=
V
R3
C1 with R1 (and C3 with R3) create an input high-pass filter with a cut-off frequency of
24.1Hz. C8 with a 16Ω load (and C9 with a 32Ω load) create an output high-pass filter with a
cut-off frequency of 45.2Hz (22.6Hz). For information on ho w t o ch ang e t he value of the cutoff frequency, refer to the datasheet.
The C2 and C4 component locations are empty in order to add a low-pass filter if required.
Table 2. Evaluation board connectors
Connector Description
Connector for setting PHG or SE configuration of the TS4909:
`
– the pins 1 and 2 are shorted, output stage is in SE mode
123
`
– the pins 2 and 3 are shorted, output stage is in PHG mode
P1
123
The connector pins are connected:
– 1 to V
CC
– 2 to SE/PHG control
– 3 to GND
P2 Pow er connector (VCC and GND). Power supply voltage from 2.2V to 5.5V.
Output signal connector. The connector pins are:
– 1&2: SE output 1 (GND and active signal)
P3
– 3&4: PHG output 1 (PHG refere nc e voltage output and active signal)
– 5&6: PHG output 2(active signal and PHG reference voltage output)
– 7&8: SE output 2 (active signal and GND)
Standby control connector:
`
– the pins 1 and 2 are shorted, the TS4909 is in operation mode
123
`
– the pins 2 and 3 are shorted, the TS4909 is in standby mode
P4
123
The connector pins are connected:
– 1 to V
CC
– 2 to standby control
– 3 to GND
P5
Input signal connector (GND and active input signal). Pins 1 and 2 for input 1 and pins
3 and 4 for input 2.
2/5
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