LM4867MTEX/NOPB National Semiconductor, LM4867MTEX/NOPB Datasheet - Page 16

• Manufacturer Part Number: LM4867MTEX/NOPB
• Description: IC AMP AUDIO PWR 3W AB 20TSSOP
• Manufacturer: National Semiconductor
• Series: Boomer®r
• Type: Class ABr

Specifications of LM4867MTEX/NOPB

• Output Type: 2-Channel (Stereo) with Stereo Headphones
• Max Output Power X Channels @ Load: 3W x 2 @ 3 Ohm; 208mW x 2 @ 16 Ohm
• Voltage - Supply: 2 V ~ 5.5 V
• Features: Depop, Input Multiplexer, Shutdown, Thermal Protection
• Mounting Type: Surface Mount
• Package / Case: 20-TSSOP Exposed Pad, 20-eTSSOP, 20-HTSSOP
• Operational Class: Class-AB
• Audio Amplifier Output Configuration: 2-Channel Stereo
• Audio Amplifier Function: Headphone/Speaker
• Total Harmonic Distortion: 0.30%%
• Single Supply Voltage (typ): 3/5V
• Dual Supply Voltage (typ): Not RequiredV
• Power Supply Requirement: Single
• Rail/rail I/o Type: No
• Power Supply Rejection Ratio: 67dB
• Single Supply Voltage (min): 2V
• Single Supply Voltage (max): 5.5V
• Dual Supply Voltage (min): Not RequiredV
• Dual Supply Voltage (max): Not RequiredV
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 20
• Package Type: TSSOP EP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM4867MTEX

www.national.com
Application Information
Equation (6) gives the maximum junction temperature
T
maximum junction temperature by reducing the power sup-
ply voltage or increasing the load resistance. Further allow-
ance should be made for increased ambient temperatures.
The above examples assume that a device is a surface
mount part operating around the maximum power dissipation
point. Since internal power dissipation is a function of output
power, higher ambient temperatures are allowed as output
power or duty cycle decreases.
If the result of Equation (2) is greater than that of Equation
(3), then decrease the supply voltage, increase the load
impedance, or reduce the ambient temperature. If these
measures are insufficient, a heat sink can be added to
reduce θ
copper area around the package, with connections to the
ground pin(s), supply pin and amplifier output pins. External,
solder attached SMT heatsinks such as the Thermalloy
7106D can also improve power dissipation. When adding a
heat sink, the θ
junction−to−case
case−to−sink
sink−to−ambient thermal impedance.) Refer to the Typical
Performance Characteristics curves for power dissipation
information at lower output power levels.
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 10µF in parallel with a 0.1µF filter capacitors to stabi-
lize 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 1.0µF
tantalum bypass capacitance connected between the
LM4867’s supply pins and ground. Do not substitute a ce-
ramic capacitor for the tantalum. Doing so may cause oscil-
lation. Keep the length of leads and traces that connect
capacitors between the LM4867’s power supply pin and
HEADPHONE (SINGLE-ENDED) AMPLIFIER
OPERATION
An internal pull−up circuit is connected to the HP−IN (pin 20)
headphone amplifier control pin. When this pin is left uncon-
nected, V
and switches Amp2A’s input signal from an audio signal to
JMAX
. If the result violates the LM4867’s 150˚C, reduce the
JA
DD
. The heat sink can be created using additional
is applied to the HP−IN. This turns off Amp2B
JA
thermal
SHUTDOWN
is the sum of θ
Logic High
Logic Low
Logic Low
Logic Low
Logic Low
T
thermal
JMAX
PIN
impedance,
= P
DMAX
impedance,
JC
, θ
θ
CS
JA
= −OUTB signal
= −OUTB signal
≠ −OUTB signal
≠ −OUTB signal
, and θ
+ T
and
(Continued)
HP-IN
A
PIN
θ
X
SA
CS
θ
SA
. (θ
Truth Table for Logic Inputs
JC
is
is
is the
the
the
(6)
MUX CHANNEL
INPUT SELECT
16
Logic High
Logic High
Logic Low
Logic Low
ground as short as possible. Connecting a 1µF capacitor,
C
internal bias voltage’s stability and improves the amplifier’s
PSRR. The PSRR improvements increase as the bypass pin
capacitor value increases. Too large, however, increases
turn−on time and can compromise the amplifier’s click and
pop performance. The selection of bypass capacitor values,
especially C
click and pop performance (as explained in the section,
Proper Selection of External Components), system cost,
and size constraints.
MICRO−POWER SHUTDOWN
The voltage applied to the SHUTDOWN pin controls the
LM4867’s shutdown function. Activate micro−power shut-
down by applying V
the LM4867’s micro−power shutdown feature turns off the
amplifier’s bias circuitry, reducing the supply current. The
logic threshold is typically V
shutdown current is achieved by applying a voltage that is as
near as V
that is less than V
Table 1 shows the logic signal levels that activate and deac-
tivate micro−power shutdown and headphone amplifier op-
eration. To ensure that the output signal remains
transient−free, do not cycle the shutdown function
faster than 1Hz.
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 100kΩ pull−up resistor between the
SHUTDOWN pin and V
SHUTDOWN pin and ground. Select normal amplifier opera-
tion by closing the switch. Opening the switch connects the
SHUTDOWN pin to V
vating micro−power shutdown. The switch and resistor guar-
antee 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.
the V
bridge-connected loads. Quiescent current consumption is
reduced when the IC is in this single−ended mode.
Figure 8 shows the implementation of the LM4867’s head-
phone control function. An internal comparator with a nomi-
nal 400mV offset monitors the signal present at the −OUTB
output. It compares this signal against the signal applied to
the HP−IN pin. When these signals are equal, as is the case
when a BTL is connected to the amplifier, the comparator
forces the LM4867 to maintain bridged−amplifier operation.
When the HP−IN pin is externally floated, such as when
X
B
, between the BYPASS pin and ground improves the
DD
/2 voltage present on pin 14. The result is muted
DD
B
as possible to the SHUTDOWN pin. A voltage
, depends on desired PSRR requirements,
OPERATIONAL MODE (MUX
Single-ended amplifiers (1)
Single-ended amplifiers (2)
DD
Micro−power shutdown
DD
Bridged amplifiers (1)
Bridged amplifiers (2)
INPUTCHANNEL #)
DD
to the SHUTDOWN pin. When active,
may increase the shutdown current.
DD
through the pull−up resistor, acti-
. Connect the switch between the
DD
/2. The low 0.7µA typical