TPA6133A2_17 Datasheet, PDF (14/26 Pages) Texas Instruments – 138-mW DirectPath Stereo Headphone Amplifier

TPA6133A2
SLOS821B – JUNE 2013 – REVISED SEPTEMBER 2014
Typical Application (continued)
9.2.1 Design Requirements
For this design example, use the following as the input parameters.
DESIGN PARAMTER
Input voltage
Minimum current limit
Maximum current limit
Table 2. Design Parameters
EXAMPLE VALUE
2.5 V – 5.5 V
4 mA
6 mA
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9.2.2 Detailed Design Procedure
9.2.2.1 Input-Blocking Capacitors
DC input-blocking capacitors block the dc portion of the audio source, and allow the inputs to properly bias.
Maximum performance is achieved when the inputs of the TPA6133A2 are properly biased. Performance issues
such as pop are optimized with proper input capacitors.
The dc input-blocking capacitors may be removed provided the inputs are connected differentially and within the
input common mode range of the amplifier, the audio signal does not exceed ±3 V, and pop performance is
sufficient.
C_IN is a theoretical capacitor used for mathematical calculations only. Its value is the series combination of the dc
input-blocking capacitors, C_{(DCINPUT-BLOCKING)}. Use Equation 3 to determine the value of C_{(DCINPUT-BLOCKING)}. For
example, if C_IN is equal to 0.22 μF, then C_{(DCINPUT-BLOCKING)} is equal to about 0.47 μF.
C_IN =
1
2
C_{(DCINPUT-BLOCKING)}
(3)
The two C_{(DCINPUT-BLOCKING)} capacitors form a high-pass filter with the input impedance of the TPA6133A2. Use
Equation 3 to calculate C_IN, then calculate the cutoff frequency using C_IN and the differential input impedance of
the TPA6133A2, R_IN, using Equation 4. Note that the differential input impedance changes with gain. The
frequency and/or capacitance can be determined when one of the two values are given.
fc_IN
+
2p
1
R_IN
C_IN
or
C_IN
+
2p
1
fc_IN
R_IN
(4)
If a high pass filter with a -3 dB point of no more than 20 Hz is desired over all gain settings, the minimum
impedance would be used in the above equation. The capacitor value by the above equation would be 0.215 μF.
However, this is C_IN, and the desired value is for C_{(DCINPUT-BLOCKING)}. Multiplying C_IN by 2 yields 0.43 μF, which is
close to the standard capacitor value of 0.47 μF. Place 0.47 μF capacitors at each input terminal of the
TPA6133A2 to complete the filter.
9.2.2.2 Charge Pump Flying Capacitor and CPVSS Capacitor
The charge pump flying capacitor serves to transfer charge during the generation of the negative supply voltage.
The CP_VSS capacitor must be at least equal to the flying capacitor in order to allow maximum charge transfer.
Low ESR capacitors are an ideal selection, and a value of 1 µF is typical.
9.2.2.3 Decoupling Capacitors
The TPA6133A2 is a DirectPath™ headphone amplifier that requires adequate power supply decoupling to
ensure that the noise and total harmonic distortion (THD) are low. Use good low equivalent-series-resistance
(ESR) ceramic capacitors, typically 1.0 µF. Find the smallest package possible, and place as close as possible to
the device V_DD lead. Placing the decoupling capacitors close to the TPA6133A2 is important for the performance
of the amplifier. Use a 10 μF or greater capacitor near the TPA6133A2 to filter lower frequency noise signals.
The high PSRR of the TPA6133A2 will make the 10 μF capacitor unnecessary in most applications.
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