MAX9757ETJ+T Maxim Integrated Products, MAX9757ETJ+T Datasheet - Page 19

• Manufacturer Part Number: MAX9757ETJ+T
• Description: IC AMP AUDIO PWR 2.3W AB 32TQFN
• Manufacturer: Maxim Integrated Products
• Series: DirectDrive™r
• Type: Class ABr

Specifications of MAX9757ETJ+T

• Output Type: 2-Channel (Stereo) with Stereo Headphones
• Max Output Power X Channels @ Load: 2.3W x 2 @ 3 Ohm; 130mW x 2 @ 16 Ohm
• Voltage - Supply: 4.5 V ~ 5.5 V
• Features: Depop, Short-Circuit and Thermal Protection, Shutdown, Volume Control
• Mounting Type: Surface Mount
• Package / Case: 32-TQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Maxim’s DirectDrive architecture uses a charge pump to
create an internal negative supply voltage. This allows the
MAX9756/MAX9757/MAX9758 headphone amplifier out-
put to be biased at GND, almost doubling the dynamic
range while operating from a single supply. With no DC
component, there is no need for the large DC-blocking
capacitors. Instead of two large capacitors (220µF, typ),
the MAX9756/MAX9757/MAX9758 charge pump requires
only two small ceramic capacitors (1µF typ), conserving
board space, reducing cost, and improving the frequen-
cy response of the headphone amplifier. See the Output
Power vs. Charge-Pump Capacitance graph in the
Typical Operating Characteristics for details of the possi-
ble capacitor values.
In addition to the cost and size disadvantages, the DC-
blocking capacitors limit the low-frequency response of
the amplifier. The impedance of the headphone load to
the DC-blocking capacitor forms a highpass filter with
the -3dB point determined by:
where R
C
The highpass filter is required by conventional single-
ended, single-supply headphone amplifiers to block the
midrail DC component of the audio signal from the
headphones. Depending on the -3dB point, the filter can
attenuate low-frequency signals within the audio band.
Figure 10. Low-Frequency Attenuation of Common DC-
Blocking Capacitor Values
Headphone Amplifiers with Automatic Level Control
OUT
is the value of the DC-blocking capacitor.
L
2.3W Stereo Speaker Amplifiers and DirectDrive
-10.5
-12.0
-13.5
-15.0
is the impedance of the headphone and
-1.5
-3.0
-4.5
-6.0
-7.5
-9.0
0
10
f
−
______________________________________________________________________________________
3
LOW-FREQUENCY ROLLOFF
dB
100
FREQUENCY (Hz)
=
33μF
(R
100μF
L
Low-Frequency Response
2 π
220μF
= 16Ω)
1k
330μF
R C
DirectDrive
L OUT
1
10k
100k
Larger values of C
physically larger, more expensive capacitors. Figure 10
shows the relationship between the size of C
the resulting low-frequency attenuation. Note that the
-3dB point for a 16Ω headphone with a 100µF-blocking
capacitor is 100Hz, well within the audio band.
The MAX9756/MAX9757/MAX9758 feature a low-noise
inverting charge pump to generate the negative rail
necessary for DirectDrive headphone operation. The
switching frequency is well beyond the audio range,
and does not interfere with the audio signals. The
switch drivers feature a controlled switching speed that
minimizes noise generated by turn-on and turn-off tran-
sients. Limiting the switching speed of the charge
pump minimizes the di/dt noise caused by the parasitic
bond wire and trace inductance.
The headphone sense input (HPS) monitors the head-
phone jack and automatically configures the MAX9756/
MAX9757/MAX9758 based upon the voltage applied at
HPS. A voltage of less than 0.8V enables the speaker
amplifier. A voltage of greater than 2V disables the
speaker amplifiers and enables the headphone ampli-
fiers. For automatic headphone detection, connect HPS
to the control pin of a 3-wire headphone jack as shown
in Figure 11. With no headphone present, the output
impedance of the headphone amplifier pulls HPS low.
When a headphone plug is inserted into the jack, the
control pin is disconnected from the tip contact and
HPS is pulled to V
Figure 11. HPS Configuration
SHUTDOWN
CONTROL
Headphone Sense Input (HPS)
DD
HPS
HPR
MAX9756/
MAX9757/
HPL
MAX9758
OUT
14kΩ
with 35µA.
reduce the attenuation but are
35μA
14kΩ
V
DD
Charge Pump
OUT
and
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