TPA6132A2 Datasheet, PDF (14/22 Pages) Texas Instruments – 25-mW DIRECTPATH™ STEREO HEADPHONE AMPLIFIER WITH POP SUPPRESSION

TPA6132A2
SLOS597 – DECEMBER 2008 ........................................................................................................................................................................................... www.ti.com
RF AND POWER SUPPLY NOISE IMMUNITY
The TPA6132A2 employs a new differential amplifier architecture to achieve high power supply noise rejection
and RF noise rejection. RF and power supply noise are common in modern electronics. Although RF frequencies
are much higher than the 20 kHz audio band, signal modulation often falls in-band. This, in turn, modulates the
supply voltage, allowing a coupling path into the audio amplifier. A common example is the 217 Hz GSM
frame-rate buzz often heard from an active speaker when a cell phone is placed nearby during a phone call.
The TPA6132A2 has excellent rejection of power supply and RF noise, preventing audio signal degradation.
CONSTANT MAXIMUM OUTPUT POWER AND ACOUSTIC SHOCK PREVENTION
Typically the output power increases with increasing supply voltage on an unregulated headphone amplifier. The
TPA6132A2 maintains a constant output power independent of the supply voltage. Thus the design for
prevention of acoustic shock (hearing damage due to exposure to a loud sound) is simplified since the output
power will remain constant, independent of the supply voltage. This feature allows maximizing the audio signal at
the lowest supply voltage.
INPUT COUPLING CAPACITORS
Input coupling capacitors block any dc bias from the audio source and ensure maximum dynamic range. Input
coupling capacitors also minimize TPA6132A2 turn-on pop to an inaudible level.
The input capacitors are in series with TPA6132A2 internal input resistors, creating a high-pass filter. Equation 3
calculates the high-pass filter corner frequency. The input impedance, RIN, is dependent on device gain. Larger
input capacitors decrease the corner frequency. See the Operating Characteristics table for input impedance
values.
1
f _C = _{2p RINCIN}
(3)
For a given high-pass cutoff frequency, the minimum input coupling capacitor is found as:
1
C_IN = _{2p ¦ CRIN}
(4)
Example: Design for a 20 Hz corner frequency with a TPA6132A2 gain of +6 dB. The Operating Characteristics
table gives RIN as 13.2 kΩ. Equation 4 shows the input coupling capacitors must be at least 0.6 µF to achieve a
20 Hz high-pass corner frequency. Choose a 0.68 µF standard value capacitor for each TPA6132A2 input (X5R
material or better is required for best performance).
Input capacitors can be removed provided the TPA6132A2 inputs are driven differentially with less than ±1 V and
the common-mode voltage is within the input common-mode range of the amplifier. Without input capacitors
turn-on pop performance may be degraded and should be evaluated in the system.
CHARGE PUMP FLYING CAPACITOR AND HPVSS CAPACITOR
The TPA6132A2 uses a built-in charge pump to generate a negative voltage supply for the headphone
amplifiers. The charge pump flying capacitor connects between CPP and CPN. It transfers charge to generate
the negative supply voltage. The HPVSS capacitor must be at least equal in value to the flying capacitor to allow
maximum charge transfer. Use low equivalent-series-resistance (ESR) ceramic capacitors (X5R material or
better is required for best performance) to maximize charge pump efficiency. Typical values are 1 µF to 2.2 µF
for the HPVSS and flying capacitors. Although values down to 0.47 µF can be used, total harmonic distortion
(THD) will increase.
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