max9702etit Maxim Integrated Products, Inc., max9702etit Datasheet - Page 20

• Manufacturer Part Number: max9702etit
• Description: Max9702 1.8w, Filterless, Stereo, Class D Audio Power Amplifier And Directdrive Stereo Headphone Amplifier
• Manufacturer: Maxim Integrated Products, Inc.

The MAX9702 features a low-noise charge pump. The
switching frequency of the charge pump is 1/2 the
switching frequency of the Class D amplifier. When
SYNC is driven externally, the charge pump switches at
1/2 f
es with a spread-spectrum pattern. The nominal switch-
ing frequency is well beyond the audio range, and thus
does not interfere with the audio signals, resulting in an
SNR of 97dB. The switch drivers feature a controlled
switching speed that minimizes noise generated by
turn-on and turn-off transients. By limiting the switching
speed of the charge pump, the di/dt noise caused by
the parasitic bond wire and trace inductance is mini-
mized. Although not typically required, additional high-
frequency noise attenuation can be achieved by
increasing the size of C2 (see Typical Application
Circuit). The charge pump is active in both speaker and
headphone modes.
The MAX9702 features an input multiplexer/mixer that
allows three different audio sources to be selected and
mixed. Command register bits 5 and 6 select the input
channel (see Table 6), and the audio signal is output to
the active amplifier. When the mono path is selected
(bit 6 = 0, bit 5 = 1), the mono input is present on both
the outputs (with a gain according to Tables 4 and 5).
When the stereo path is selected, the left and right
inputs are present on the outputs (with a gain accord-
ing to Tables 4 and 5). When in mixer mode, the mono
input is added to each of the stereo inputs and present
at the output (with a gain according to Tables 4 and 5).
The mono and stereo signals are attenuated by 6dB
prior to mixing to maintain dynamic range. In mute,
none of input signals is present at output.
The headphone sense input (HPS) monitors the head-
phone jack, and automatically configures the MAX9702
based on the voltage applied at HPS. A voltage of less
than 0.8V sets the MAX9702 to speaker mode. A volt-
age of greater than 2V disables the bridge amplifiers
and enables the headphone amplifiers.
For automatic headphone detection, connect HPS to
the control pin of a 3-wire headphone jack as shown in
Figure 8. With no headphone present, the output
impedance of the headphone amplifier pulls HPS to
less than 0.8V. When a headphone plug is inserted into
the jack, the control pin is disconnected from the tip
1.8W, Filterless, Stereo, Class D Audio Power
Amplifier and DirectDrive Stereo Headphone Amplifier
20
SYNC
______________________________________________________________________________________
. When SYNC = V
Headphone Sense Input (HPS)
DD
, the charge pump switch-
Input Multiplexer/Mixer
Charge Pump
contact and HPS is pulled to V
600kΩ pullup resistor. When driving HPS from an exter-
nal logic source, drive HPS low when the MAX9702 is
shut down. Place a 10kΩ resistor in series with HPS and
the headphone jack to ensure ±8kV ESD protection.
The MAX9702 features comprehensive click-and-pop
suppression that eliminates audible transients on start-
up and shutdown. While in shutdown, the H-bridge is
in a high-impedance state. During startup or power-up,
the input amplifiers are muted and an internal loop sets
the modulator bias voltages to the correct levels, pre-
venting clicks and pops when the H-bridge is subse-
quently enabled.
The MAX9702 features current limiting and thermal pro-
tection to protect the device from short circuits and
overcurrent conditions. The headphone amplifier puls-
es in the event of an overcurrent condition. The speaker
amplifiers’ current-limiting protection clamps the output
current without shutting down the outputs. This can
result in a distorted output.
The MAX9702 has thermal protection that disables the
device into shutdown at +120°C until the temperature
decreases to +110°C.
Figure 8. HPS Configuration
SHDN
SDA
SCL
Current-Limit and Thermal Protection
SHUTDOWN
CONTROL
MAX9702
Click-and-Pop Suppression
HPS
HPL
HPR
10kΩ
100kΩ
10kΩ
V
DD
DD
through the internal