®
LY8661
Rev. 1.8
Dual 2.0W/CH Stereo Audio Amplifier include Headphone Function
APPLICATION INFORMATION
The LY8661’s QFN package provides a low thermal resistance between the die and the PCB to which the part
is mounted and soldered. This allows rapid heat transfer from the die to the surrounding PCB copper traces,
ground plane and, finally, surrounding air. The result is a low voltage audio power amplifier that produces
2.0W at 10% THD with a 4ꢀ load. This high power is achieved through careful consideration of necessary
thermal design. Failing to optimize thermal design may compromise the LY8661’s high power performance
and activate unwanted, though necessary, thermal shutdown protection.
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 LY8661’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 LY8661’s power supply pin and ground as short as possible.
MICRO-POWER SHUTDOWN
The voltage applied to the SHUTDOWN pin controls the LY8661’s shutdown function. Activate micro-power
shutdown by applying GND to the SHUTDOWN pin. When active, the LY8661’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 GND as possible to the SHUTDOWN pin. A
voltage that is more than GND 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 Ground. Connect the switch between the SHUTDOWN pin VDD. Select
normal amplifier operation by closing the switch. Opening the switch sets the SHUTDOWN pin to ground
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
Headphone Jack
Sense Pin
Operational Output
Mode
Shutdown Pin
Logic High
Logic High
Logic Low
Low (HP not Plugged in)
High (HP Plugged in)
High or Low Don’t care
BTL
Single-Ended
Micro-Power Shutdown
HEADPHONE SENSE AND HEADPHONE LOGIC IN FUNCTIONS
Applying a logic level to the LY8661’s HP Sense 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 2 shows the implementation of the LY8661’s headphone control function. With no headphones
connected to the headphone jack, the R5-R6 voltage divider sets the voltage applied to the HP Sense pin (pin
14) at approximately 50mV. This 50mV enables Amp A (+out) and Amp B (+out) placing the LY8661 in
bridged mode operation.
While the LY8661 operates in bridged mode, the DC potential across the load is essentially 0V. 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 R7
to pull the HP Sense pin up to VDD.
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
10
FAX: 886-3-6668836
