®
LY8663
Dual 2.0W/CH Stereo Audio Amplifier include Headphone Function with
Active-high shutdown mode
Rev. 1.7
APPLICATION INFORMATION
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is critical for low noise performance and high power
supply rejection. Applications that employ a 5V regulator typically use a 10 μF in parallel with a 0.1 μF filter
capacitor to stabilize the regulator’s output, reduce noise on the supply line, and improve the supply’s
transient response. However, their presence does not eliminate the need for a local 1.0 μF tantalum bypass
capacitance connected between the LY8663’s supply pins and ground. Do not substitute a ceramic capacitor
for the tantalum. Doing so may cause oscillation. Keep the length of leads and traces that connect capacitors
between the LY8663’s power supply pin and ground as short as possible.
MICRO-POWER SHUTDOWN
The voltage applied to the SHUTDOWN pin controls the LY8663’s shutdown function. Activate micro-power
shutdown by applying VDD to the SHUTDOWN pin. When active, the LY8663’s micro-power shutdown
feature turns off the amplifier’s bias circuitry, reducing the supply current. The low 0.1 μA typical shutdown
current is achieved by applying a voltage that is as near as VDD as possible to the SHUTDOWN pin. A
voltage that is less than VDD may increase the shutdown current.
Table 1 shows the logic signal levels that activate and deactivate micro-power shutdown and headphone
amplifier operation.
There are a few ways to control the micro-power shutdown. These include using a single-pole, single-throw
switch, a microprocessor or a microcontroller. When using a switch, connect an external 20k resistor between
the SHUTDOWN pin and VDD. Connect the switch between the SHUTDOWN pin and GND. Select normal
amplifier operation by closing the switch. Opening the switch sets the SHUTDOWN pin to VDD through the
20k resistor, which activates the micro-power shutdown. The switch and resistor guarantee that the
SHUTDOWN pin will not float. This prevents unwanted state changes. In a system with a microprocessor or a
microcontroller, use a digital output to apply the control voltage to the SHUTDOWN pin. Driving the
SHUTDOWN pin with active circuitry eliminates the pull up resistor.
TABLE 1. Logic Level Truth Table
Operational Output
Shutdown Pin
HP-IN Pin
Mode
Logic Low
Logic Low
Logic High
Low (HP not Plugged in)
High (HP Plugged in)
High or Low Don’t care
BTL
Single-Ended
Micro-Power Shutdown
HP-IN FUNCTIONS
Applying a voltage between 4V and VDD level to the LY8663’s HP-IN headphone control pin turns off Amp. A
(+out) and Amp. B (+out) muting a bridged-connected load. Quiescent current consumption is reduced when
the IC is in this single-ended mode.
Figure 3 shows the implementation of the LY8663’s headphone control function. With no headphones
connected to the headphone jack, the R3,R8 voltage divider sets the voltage applied to the HP-IN pin (pin 20)
at approximately 50mV. This 50mV enables Amp A (+out) and Amp B (+out) placing the LY8663 in bridged
mode operation.
While the LY8663 operates in bridged mode, the DC potential across the load is essentially 0V. The HP-IN
threshold is set at 4V. Therefore, even in an ideal situation, the output swing cannot cause a false single
-ended trigger. Connecting headphones to the headphone jack disconnects the headphone jack contact pin
from −OUTA and allows R8 to pull the HP-IN pin up to VDD.
This enables the headphone function, turns off Amp A (+out) and Amp B (+out) and mutes the bridged
speaker. The amplifier then drives the headphones, whose impedance is in parallel with resistors R3 and R4.
These resistors have negligible effect on the LY8663’s output drive capability since the typical impedance of
headphones is 32ꢀ.
Figure 3 also shows the suggested headphone jack electrical connections. The jack is designed to mate with
a three wire plug. The plug’s tip and ring should each carry one of the two stereo output signals, whereas the
Lyontek Inc. reserves the rights to change the specifications and products without notice.
5F, No. 2, lndustry E . Rd. IX, Science-Based Industrial Park, Hsinchu 300, Taiwan
TEL: 886-3-6668838
8
FAX: 886-3-6668836
