NE58633_3 © NXP B.V. 2010. All rights reserved.
Product data sheet Rev. 03 — 19 January 2010 15 of 27
NXP Semiconductors
NE58633
Noise reduction class-D headphone driver amplifier
10.2 Power supply decoupling
The power supply pins B_IN, PVDDL and PVDDR are decoupled with 1 μF capacitors
directly from the pins to ground.
10.3 Speaker output filtering considerations
The ferrite beads form a low-pass filter with a shunt capacitor to reduce radio
frequency > 1 MHz. Choose a ferrite bead with high-impedance at high frequencies and
low-impedance at low frequencies. A typical ferrite bead is 600 Ω at 100 MHz. A shunt
capacitor is added after the ferrite bead to complete the low-pass filter. The low frequency
impedance is not as important as in power amplifiers because headphone speakers are
stabilized with a series impedance of about 18 Ω on each output. The series resistors, R
s
,
may be decreased to increase the power delivered to the speaker load. Figure 7
and
Figure 8
show the THD+N versus P
o
performance for R
s
=0Ω and R
s
=18Ω.
10.4 Boost converter and layout considerations
10.4.1 Boost converter operation
The boost converter operates in asynchronous mode as shown in Figure 15. As V
BAT
drops, the boost converter efficiency decreases (see Figure 3
and Figure 6). The boost
converter is capable of driving 2.65 mA external load (see Figure 5
).
If the NE58633 is operated without the boost converter, pins B_IN, PVDDL and PVDDR
may be powered directly from a 3 V power supply source such as 2 AAA alkaline
batteries. The VBAT pin is not used.
(1) Positive or negative output of the class-D driver with V
BAT
at 1.5 V.
(2) Pin BS (V
BS
= V
bst
).
Remark: This is a normal pulse. It does not change with V
BAT
but remains at the level of the boosted voltage.
(3) Current at pin B_IN (I
bst(load)O
) measures approximately 40 mA peak, but averaged DC current is a few milliamperes per the
specification.
Fig 15. Switching waveform at the BS pin
002aad95
(1)
(2)
(3)
2 Gs/s
