LM4867MTE National Semiconductor, LM4867MTE Datasheet - Page 17

• Manufacturer Part Number: LM4867MTE
• Manufacturer: National Semiconductor

Specifications of LM4867MTE

• Operational Class: Class-AB
• Audio Amplifier Output Configuration: 2-Channel Stereo
• Output Power (typ): 3W
• 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
• Unity Gain Bandwidth Product (typ): 3.5MHz
• 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: Not Compliant

Application Information
headphones are connected to the jack shown in Figure 8,
and internal pull−up forces V
HP−IN inputs. This changes the comparator’s output state
and enables the headphone function: it turns off Amp2B,
switches Amp2A’s input signal from an audio signal to the
V
connected loads. Amp1A and Amp1B drive the headphones.
Figure 8 also shows the suggested headphone jack electri-
cal 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 sleeve
provides the return to Amp2A. A headphone jack with one
control pin contact is sufficient to drive the HP−IN pin when
connecting headphones.
A switch can replace the headphone jack contact pin. When
a switch shorts the HP−IN pin to V
speakers are muted and Amp1A and Amp2A drive a pair of
headphones. When a switch shorts the HP−IN pin to GND,
the LM4867 operates in bridge mode. If headphone drive is
not needed, short the HP−IN pin to the −OUTB pin.
SINGLE-ENDED OUTPUT POWER PERFORMANCE
AND MEASUREMENT CONSIDERATIONS
The LM4867 delivers clean, low distortion SE output power
into loads that are greater than 10Ω. As an example, output
power for 16Ω and 32Ω loads are shown in the Typical
Performance Characteristic curves. For loads less than
10Ω, the LM4876 can typically supply 180mW of low distor-
tion power. However, when higher dissipation is desired in
loads less than 10Ω, a dramatic increase in THD+N may
occur. This is normal operation and does not indicate that
proper functionality has ceased. When a jump from moder-
ate to excessively high distortion is seen, simply reducing
the output voltage swing will restore the clean, low distortion
SE operation.
The dramatic jump in distortion for loads less than 10Ω
occurs when current limiting circuitry activates. During SE
operation, AMP2A (refer to Figure 4) drives the headphone
DD
FIGURE 7. The PCDN042 provides additional ESD protection beyond the 8000V shown in the Absolute Maximum
/2 voltage present on pin 14, and mutes the bridge-
DD
on the internal comparator’s
DD
, bridge−connected
(Continued)
Ratings for the AMP2A output
17
Figure 7 shows an optional resistor connected between the
amplifier output that drives the headphone jack sleeve and
ground. This resistor provides a ground path that supressed
power supply hum. This hum may occur in applications such
as notebook computers in a shutdown condition and con-
nected to an external powered speaker. The resistor’s 100Ω
value is a suggested starting point. Its final value must be
determined based on the tradeoff between the amount of
noise suppression that may be needed and minimizing the
additional current drawn by the resistor (25mA for a 100Ω
resistor and a 5V supply).
ESD PROTECTION
As stated in the Absolute Maximum Ratings, pin 28 on the
MT and MH packages have a maximum ESD susceptibility
rating of 8000V. For higher ESD voltages, the addition of a
PCDN042 dual transil (from California Micro Devices), as
shown in Figure 7, will provide additional protection.
sleeve. An on-board circuit monitors this amplifier’s output
current. The sudden increase in THD+N is caused by the
current limit circuitry forcing AMP2A into a high−impedance
output mode. When this occurs, the output waveform has
discontinuities that produce large amounts of distortion. It
has been observed that as the output power is steadily
increased, the distortion may jump from 5% to greater than
35%. Indeed, 10% THD+N may not actually be achievable.
USING THE SINGLE−ENDED OUTPUT FOR LINE
LEVEL APPLICATIONS
Some samples of the LM4867 may exhibit small amplitude,
high frequency oscillation when the SE output is connected
to a line-level input. This oscillation can be eliminated by
connecting a 5%, 300Ω resistor between Amp2A’s output pin
and each amplifier, AMP1A and AMP1B, output.
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