max9722beue Maxim Integrated Products, Inc., max9722beue Datasheet - Page 15

• Manufacturer Part Number: max9722beue
• Description: 5v, Differential Input, Directdrive, 130mw Stereo Headphone Amplifiers With Shutdown Products
• Manufacturer: Maxim Integrated Products, Inc.

to the capacitive nature of the piezoelectric speaker, as
frequency increases, the speaker impedance decreas-
es, resulting in a larger current draw from the amplifier.
Furthermore, the capacitive nature of the speaker can
cause the MAX9722 to become unstable. In these
tests, the MAX9722 exhibited instabilities when driving
the WM-R57A. A simple inductor/resistor network in
series with the speaker isolates the speaker’s capaci-
tance from the amplifier, and ensures the device output
sees a resistive load of about 10Ω at high frequency
maintaining stability. Although the MAX9722 was not
stable with the WM-R57A, a different speaker with dif-
ferent characteristics may result in stable operation,
and elimination of the isolation components.
Proper layout and grounding are essential for optimum
performance. Connect PGND and SGND together at a
single point on the PC board. Connect all components
associated with the charge pump (C2 and C3) to the
PGND plane. Connect PV
device. Connect PV
Bypassing of both supplies is accomplished by charge-
pump capacitors C2 and C3 (see the Typical Application
Circuit ). Place capacitors C2 and C3 as close to the
device as possible. Route PGND and all traces that carry
switching transients away from SGND and the traces
and components in the audio signal path. Refer to the
MAX9722 evaluation kit for layout guidelines.
Figure 12. MAX9722 THD+N vs. Frequency
Stereo Headphone Amplifiers with Shutdown
0.0001
0.001
0.01
0.1
10
1
10
TOTAL HARMONIC DISTORTION PLUS
V
A
V
OUTPUTS DRIVING
PIEZOELECTRIC SPEAKER
5V, Differential Input, DirectDrive, 130mW
DD
V
OUT(P-P)
= -1V/V
= 5V
______________________________________________________________________________________
SS
NOISE vs. FREQUENCY
100
= 2V
and SV
FREQUENCY (Hz)
DD
Layout and Grounding
1k
and SV
SS
together at the device.
10k
DD
together at the
100k
Figure 13. MAX9722 Capacitive-Load Stability Waveform:
(a) Falling Edge, (b) Rising Edge
Figure 14. Isolation Network Improves Stability
AUDIO
INPUT
1µF 10kΩ
A
B
INR
10kΩ
MAX9722A
4µs/div
2µs/div
OUTR
OUTL
INL
10kΩ
10kΩ
100µH
10Ω
500mV/div
500mV/div
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