TPA6132A2
SLOS597–DECEMBER 2008........................................................................................................................................................................................... www.ti.com
GAIN CONTROL
The TPA6132A2 has four gain settings which are controlled with pins G0 and G1. The following table gives an
overview of the gain function.
G0 VOLTAGE
≤ 0.5 V
G1 VOLTAGE
≤ 0.5 V
AMPLIFIER GAIN
–6 dB
0 dB
3 dB
6 dB
≥ 1.3 V
≤ 0.5 V
≤ 0.5 V
≥ 1.3 V
≥ 1.3 V
≥ 1.3 V
Table 1. Windows Vista™ Premium Mobile Mode Specifications
Windows Premium Mobile Vista
Device Type
Requirement
TPA6132A2 Typical Performance
Specifications
THD+N
≤ –65 dB FS [20 Hz, 20 kHz]
–75 dB FS[20 Hz, 20 kHz]
–100 dB FS A-Weight
Analog Speaker Line Jack
(RL = 10 kΩ, FS = 0.707
Vrms)
Dynamic Range with Signal
Present
≤ –80 dB FS A-Weight
Line Output Crosstalk
THD+N
≤ –60 dB [20 Hz, 20 kHz]
–90 dB [20 Hz, 20 kHz]
≤ –45 dB FS [20 Hz, 20 kHz]
–65 dB FS [20 Hz, 20 kHz]
Analog Headphone Out Jack
(RL = 32Ω, FS = 0.300
Vrms)
Dynamic Range with Signal
Present
≤ –80 dB FS A-Weight
–94 dB FS A-Weight
Headphone Output Crosstalk
≤ –60 dB [20 Hz, 20 kHz]
–90 dB [20 Hz, 20 kHz]
HEADPHONE AMPLIFIERS
Single-supply headphone amplifiers typically require dc-blocking capacitors to remove dc bias from their output
voltage. The top drawing in Figure 25 illustrates this connection. If dc bias is not removed, large dc current will
flow through the headphones which wastes power, clip the output signal, and potentially damage the
headphones.
These dc-blocking capacitors are often large in value and size. Headphone speakers have a typical resistance
between 16 Ω and 32 Ω. This combination creates a high-pass filter with a cutoff frequency as shown in
Equation 1, where RL is the load impedance, CO is the dc-block capacitor, and fC is the cutoff frequency.
1
f
=
c
2pR C
L
O
(1)
For a given high-pass cutoff frequency and load impedance, the required dc-blocking capacitor is found as:
1
CO
=
2p ¦C RL
(2)
Reducing fC improves low frequency fidelity and requires a larger dc-blocking capacitor. To achieve a 20 Hz
cutoff with 16 Ω headphones, CO must be at least 500 µF. Large capacitor values require large packages,
consuming PCB area, increasing height, and increasing cost of assembly. During start-up or shutdown the
dc-blocking capacitor has to be charged or discharged. This causes an audible pop on start-up and power-down.
Large dc-blocking capacitors also reduce audio output signal fidelity.
Two different headphone amplifier architectures are available to eliminate the need for dc-blocking capacitors.
The Capless amplifier architecture is similar provides a reference voltage to the headphone connector shield pin
as shown in the middle drawing of Figure 25. The audio output signals are centered around this reference
voltage, which is typically half of the supply voltage to allow symmetrical output voltage swing.
When using a Capless amplifier do not connect the headphone jack shield to any ground reference or large
currents will result. This makes Capless amplifiers ineffective for plugging non-headphone accessories into the
headphone connector. Capless amplifiers are useful only with floating GND headphones.
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Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s) :TPA6132A2
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