MAX9720 Maxim, MAX9720 Datasheet - Page 16

• Manufacturer Part Number: MAX9720
• Description: 50mW / DirectDrive / Stereo Headphone Amplifier with SmartSense and Shutdown
• Manufacturer: Maxim

Use capacitors with an ESR less than 100mΩ for opti-
mum performance. Low-ESR ceramic capacitors mini-
mize the output resistance of the charge pump. For
best performance over the extended temperature
range, select capacitors with an X7R dielectric. Table 2
lists suggested manufacturers.
The value of the flying capacitor (C1) affects the charge
pump’s load regulation and output impedance. 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. In most applications, 1µF for both C1
and C2 provides adequate performance. Increasing
the value of C1 improves load regulation and reduces
the charge-pump output resistance to an extent. See
the Output Power vs. Charge Pump Capacitance and
Load Resistance graph in the Typical Operating
Characteristics. Above 2.2µF, the on-resistance of the
switches and the ESR of C1 and C2 dominate.
The hold capacitor value and ESR directly affect the
ripple on PV
put ripple. Likewise, decreasing the ESR of C2 reduces
both ripple and output impedance. Lower capacitance
values can be used in systems with low maximum out-
put power levels. See the Output Power vs. Charge-
Pump Capacitance and Load Resistance graph in the
Typical Operating Characteristics.
The power-supply bypass capacitor (C3) lowers the
output impedance of the power supply and reduces the
impact of the MAX9720’s charge-pump switching tran-
sients. Bypass V
place it physically close to the device.
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
Table 2. Suggested Capacitor Manufacturers
16
Taiyo Yuden
TDK
______________________________________________________________________________________
SUPPLIER
SS
. Increasing the value of C2 reduces out-
DD
Charge-Pump Capacitor Selection
with C3, the same value as C1, and
Power-Supply Bypass Capacitor
800-348-2498
847-803-6100
PHONE
Flying Capacitor (C1)
Hold Capacitor (C2)
847-925-0899
847-390-4405
FAX
The TIME capacitor (C
time. The debounce time is the delay between HPS
exceeding 0.8 x V
SmartSense routine. The delay ensures that any exces-
sive contact bounce caused by the insertion of a head-
phone plug into the jack does not cause HPS to
register an invalid state (Figure 9). The value of the
C
C
200nF to 600nF range are recommended.
The addition of a digital potentiometer provides simple,
digital volume control. Figure 10 shows the MAX9720
with the MAX5408 dual log taper digital potentiometer
used as an input attenuator. Connect the high terminal
of the MAX5408 to the audio input, the low terminal to
GND, and the wiper to C
position passes the audio signal unattenuated. Setting
the wiper to the lowest position fully attenuates the input.
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. Bypassing of both the positive and negative
supplies is accomplished by the charge-pump capaci-
tors, C2 and C3 (see Typical Application Circuit). Place
capacitors C1 and C3 as close to the device as possi-
ble. Place capacitor C2 as close to PV
Route PGND and all traces that carry switching tran-
sients away from SGND, traces, and components in the
audio signal path.
TIME
TIME
www.t-yuden.com
www.component.tdk.com
in nF equals the nominal delay time in ms, i.e.,
= 10nF = t
DELAY
DD
TIME
IN
= 10ms. C
Adding Volume Control
and the execution of the
SS
. Setting the wiper to the top
WEBSITE
Layout and Grounding
) sets the HPS debounce
and SV
TIME
SS
TIME Capacitor
SS
together at the
values in the
as possible.