MAX98090BEWJ+T Maxim Integrated, MAX98090BEWJ+T Datasheet - Page 139

• Manufacturer Part Number: MAX98090BEWJ+T
• Description: Interface - CODECs 5V 130mW Stereo Headphone Amp
• Manufacturer: Maxim Integrated

MAX98090
DirectDrive Headphone Output Amplifier
Traditional single-supply headphone amplifiers have out-
puts biased at a nominal DC voltage (typically at either
half the high-side supply, or at a bandgap referenced
common mode level). As a result, large coupling capaci-
tors are needed to block this DC bias and AC-couple
the audio output to the headphone load. Without these
capacitors, a significant DC current would flow through
the ground referenced headphone load. The result is both
unnecessary power dissipation, and potential damage to
both the headphone load and amplifier.
Maxim’s second-generation DirectDrive architecture
solves this problem by using a charge pump to create
an internal negative supply voltage. This increases the
overall output signal swing while at the same time, allow-
ing the headphone outputs to be biased at GND even
while operating from a single supply (Figure 39). Without
a DC bias component, there is no need for the large
AC-coupling capacitors. Instead of two large (typically
220µF) capacitors, the charge pump only requires three
small ceramic capacitors. This conserves board space,
Table 74. Charge-Pump Operating Ranges
Figure 39. Conventional vs. DirectDrive Headphone Output Bias
www.maximintegrated.com
RANGE
1
2
3
V
V
HPVDD
HPVDD
GND
2
OUTPUT LEVEL
(% of V
HEADPHONE
CONVENTIONAL HEADPHONE BIAS
10 to 25
< 10
> 25
HPVDD
)
V
HP_OUT
FREQUENCY
(kHz)
~660
~500
~82
reduces cost, and improves the frequency response of
the headphone amplifier.
Class H Amplifier Charge Pump
A Class H amplifier has the same output architecture as
a Class AB amplifier. However, in a Class H amplifier the
power supplies are modulated by the output signal. The
integrated headphone charge pump generates both the
positive and negative power supply for the headphone
output amplifier. To maximize efficiency, both the charge
pump’s switching frequency and output voltage level and
format change based on the headphone output signal level.
The charge pump has three different operating ranges
each with a different switching frequency. The two lower
power ranges use a three-level switching scheme to gen-
erate half supply rails at ±V
range uses a standard two-level switching scheme to
generate full supply rails at ±V
quency and voltage levels of each range are optimized to
maintain high efficiency while meeting the different output
power requirements (Table 74).
+V
-V
Ultra-Low Power Stereo Audio Codec
HPVDD
HPVDD
GND
CHARGE PUMP CONFIGURATION
V
CPVDD/CPVSS
±V
±V
±V
DIRECTDRIVE HEADPHONE BIAS
HPVDD
HPVDD
HPVDD
/2
/2
HPVDD
HPVDD
/2 while the high power
V
Maxim Integrated │ 139
HP_OUT
. The switching fre-
WAVEFORM
Range 1
Range 2
Range 3