max9758etjt Maxim Integrated Products, Inc., max9758etjt Datasheet - Page 23

• Manufacturer Part Number: max9758etjt
• Description: 2.3w Stereo Speaker Amplifiers And Directdrive Headphone Amplifiers With Automatic Level Control
• Manufacturer: Maxim Integrated Products, Inc.

The value of the flying capacitor (C1) affects the load
regulation and output resistance of the charge pump. A
C1 value that is too small degrades the device’s ability to
provide sufficient current drive, which leads to a loss of
output voltage. Increasing the value of C1 improves load
regulation and reduces the charge-pump output resis-
tance to an extent. See the Output Power vs. Charge-
Pump Capacitance graph in the Typical Operating
Characteristics. Above 2.2µF, the on-resistance of the
switches and the ESR of C1 and C2 dominate.
The output capacitor value and ESR directly affect the
ripple at CPV
output ripple. Likewise, decreasing the ESR of C2
reduces both ripple and output resistance. Lower
capacitance values can be used in systems with low
maximum output power levels. See the Output Power
vs. Charge-Pump Capacitance graph in the Typical
Operating Characteristics.
The CPV
impedance of the power supply and reduces the impact
of the MAX9756/MAX9757/MAX9758’s charge-pump
switching transients. Bypass CPV
value as C1, and place it physically close to CPV
PGND (refer to the MAX9756/MAX9757/MAX9758
Evaluation Kit for a suggested layout).
An additional benefit of the MAX9756/MAX9757/
MAX9758 is the internally generated negative supply
voltage (CPV
MAX9757/MAX9758 to provide the negative supply for
the headphone amplifiers. It can also be used to power
other devices within a design. Current draw from
CPV
the operation of the headphone amplifier. A typical
application is a negative supply to adjust the contrast
of LCD modules.
Headphone Amplifiers with Automatic Level Control
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should be limited to 5mA; exceeding this affects
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2.3W Stereo Speaker Amplifiers and DirectDrive
bypass capacitor (C3) lowers the output
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. Increasing the value of C2 reduces
). CPV
______________________________________________________________________________________
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Powering Other Circuits
from a Negative Supply
is used by the MAX9756/
CPV
Output Capacitor (C2)
Flying Capacitor (C1)
DD
DD
Bypass Capacitor
with C3, the same
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and
When considering the use of CPV
note that the charge-pump voltage of CPV
proportional to CPV
Proper layout and grounding are essential for optimum
performance. Use large traces for the power-supply
inputs and amplifier outputs to minimize losses due to
parasitic trace resistance, as well as route heat away
from the device. Good grounding improves audio per-
formance, minimizes crosstalk between channels, and
prevents any switching noise from coupling into the
audio signal. Connect CPGND, PGND, and GND
together at a single point on the PC board. Route
CPGND and all traces that carry switching transients
away from GND, PGND, and the traces and compo-
nents in the audio signal path.
Connect all components associated with the charge
pump (C2 and C3) to the CPGND plane. Connect V
and CPV
pump capacitors (C1, C2, and C3) as close to the
device as possible. Bypass HPV
1µF capacitor to GND. Place the bypass capacitors as
close to the device as possible.
Use large, low-resistance output traces. As load imped-
ance decreases, the current drawn from the device out-
puts increase. At higher current, the resistance of the
output traces decrease the power delivered to the load.
For example, when compared to a 0Ω trace, a 100mΩ
trace reduces the power delivered to a 4Ω load from
2.1W to 2W. Large output, supply, and GND traces also
improve the power dissipation of the device. The
MAX9756/MAX9757/MAX9758 thin QFN package fea-
tures an exposed thermal pad on its underside. This pad
lowers the package’s thermal resistance by providing a
direct-heat conduction path from the die to the PC
board. Connect the exposed thermal pad to GND by
using a large pad and multiple vias to the GND plane.
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together at the device. Place the charge-
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and is not a regulated voltage.
Layout and Grounding
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and PV
in this manner,
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is roughly
with a
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