MAX9787 Maxim Integrated Products, MAX9787 Datasheet - Page 12

• Manufacturer Part Number: MAX9787
• Description: 2.2W Stereo Audio Power Amplifier
• Manufacturer: Maxim Integrated Products

The CPV
impedance of the power supply and reduces the
impact of the MAX9787’s charge-pump switching tran-
sients. Bypass CPV
and place it physically close to the CPV
(refer to the MAX9750 Evaluation Kit for a suggested
layout).
An additional benefit of the MAX9787 is the internally
generated negative supply voltage (CPV
vides the negative supply for the amplifiers. It can also
be used to power other devices within a design.
Current draw from CPV
exceeding this affects the operation of the amplifier. A
typical application is a negative supply to adjust the
contrast of LCD modules.
When considering the use of CPV
note that the charge-pump voltage of CPV
proportional to PV
charge-pump output impedance plot appears in the
Typical Operating Characteristics.
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 head away
from the device. Good grounding improves audio per-
formance, minimizes crosstalk between channels, and
prevents any switching noise from coupling into the
2.2W Stereo Audio Power Amplifier
with Analog Volume Control
12
______________________________________________________________________________________
DD
bypass capacitor (C3) lowers the output
DD
DD
and is not a regulated voltage. The
with C3, the same value as C1,
Powering Other Circuits
SS
from a Negative Supply
Layout and Grounding
should be limited to 5mA;
CPV
DD
SS
Bypass Capacitor
in this manner,
SS
DD
). CPV
SS
and PGND
is roughly
SS
pro-
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 PV
tor 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 MAX9787 thin QFN features and exposed thermal
pad on its underside. This pad lowers the package’s
thermal resistance by providing a direct heat conduc-
tion 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.
TRANSISTOR COUNT: 9591
PROCESS: BiCMOS
SS
together at the device. Place the charge-
Chip Information
DD
with a 0.1µF capaci-
SS