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PDF LM4916 Data sheet ( Hoja de datos )
| Número de pieza | LM4916 | |
| Descripción | 1.5V/ Mono 85mW BTL Output/ 14mW Stereo Headphone Audio Amplifier | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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July 2003
LM4916
1.5V, Mono 85mW BTL Output, 14mW Stereo Headphone
Audio Amplifier
General Description
The unity gain stable LM4916 is both a mono differential
output (for bridge-tied loads or BTL) audio power amplifier
and a Single Ended (SE) stereo headphone amplifier. Oper-
ating on a single 1.5V supply, the mono BTL mode delivers
85mW into an 8Ω load at 1% THD+N. In Single Ended stereo
headphone mode, the amplifier delivers 14mW per channel
into a 16Ω load at 1% THD+N.
With the LM4916 packaged in the MM and LLP packages,
the customer benefits include low profile and small size.
These packages minimize PCB area and maximizes output
power.
The LM4916 features circuitry that reduces output transients
("clicks" and "pops") during device turn-on and turn-off, an
externally controlled, low-power consumption, active-low
shutdown mode, and thermal shutdown. Boomer audio
power amplifiers are designed specifically to use few exter-
nal components and provide high quality output power in a
surface mount package.
Key Specifications
n Mono-BTL output power
n (RL = 8Ω, VDD = 1.5V, THD+N = 1%)
85mW (typ)
n Stereo Headphone output power
n (RL = 16Ω, VDD = 1.5V, THD+N = 1%) 14mW (typ)
n Micropower shutdown current
0.02µA (typ)
n Supply voltage operating range
0.9V < VDD < 2.5V
n PSRR 1kHz, VDD = 1.5V
66dB (typ)
Features
n Single-cell 0.9V to 2.5V battery operation
n BTL mode for mono speaker
n Single ended headphone operation with coupling
capacitors
n Unity-gain stable
n "Click and pop" suppression circuitry
n Active low micropower shutdown
n Low current, active-low mute mode
n Thermal shutdown protection circuitry
Applications
n Portable one-cell audio products
n Portable one-cell electronic devices
Typical Application
FIGURE 1. Block Diagram
20048701
Boomer® is a registered trademark of National Semiconductor Corporation.
© 2003 National Semiconductor Corporation DS200487
www.national.com
1 page  
Note 10: When operating on a power supply voltage of 0.9V, the LM4916 willl not function below 0˚C. At a power supply voltage of 1V or greater, the LM4916 will
operate down to -40˚C.
Note 11: Ripple on power supply line should not exceed 400mVpp.
Typical Performance Characteristics
THD+N vs Frequency
VDD = 1.5V, PO = 5mW, RL = 16Ω
BW < 80kHz, Single Ended Output
THD+N
vs Frequency
VDD = 1.5V, RL = 8Ω, PO = 25mW
BTL Output, AV = -1
200487C2
THD+N
vs Frequency
VDD = 1.2V, PO = 5mW
RL = 16Ω, Single Ended Output, AV = -1
200487D5
THD+N
vs Frequency
VDD = 1.2V, RL = 8Ω, PO = 25mW
BTL Output, AV = -1
200487D0
200487D6
5 www.national.com
5 Page 
Typical Performance Characteristics (Continued)
Mute Attenuation
vs Load Resistance
Shutdown Current
Distribution
200487F2
200487F7
Application Information
SINGLE ENDED (SE) CONFIGURATION EXPLANATION
As shown in Figure 2, the LM4916 has two operational
amplifiers internally, which have externally configurable gain.
The closed loop gain of the two configurable amplifiers is set
by selecting the ratio of Rf to Ri. Consequently, the gain for
each channel of the IC is
AVD = -(Rf / Ri)
When the LM4916 operates in Single Ended mode, coupling
capacitors are used on each output (VoA and VoB) and the
SE/BTL pin (Pin 8) is connected to ground. These output
coupling capacitors blocks the half supply voltage to which
the output amplifiers are typically biased and couples the
audio signal to the headphones or other single-ended (SE)
loads. The signal return to circuit ground is through the
headphone jack’s sleeve.
BRIDGED (BTL) CONFIGURATION EXPLANATION
As shown in Figure 3, the LM4916 has two internal opera-
tional amplifiers. The first amplifier’s gain is externally con-
figurable, while the second amplifier should be externally
fixed in a unity-gain, inverting configuration. The closed-loop
gain of the first amplifier is set by selecting the ratio of Rf to
Riwhile the second amplifier’s gain should be fixed by the
two external 20kΩ resistors. Figure 3 shows that the output
of amplifier one serves as the input to amplifier two which
results in both amplifiers producing signals identical in mag-
nitude, but out of phase by 180˚. Consequently, the differen-
tial gain for the IC is
AVD = 2 *(Rf / Ri).
By driving the load differentially through outputs Vo1 and
Vo2, an amplifier configuration commonly referred to as
"bridged mode" is established. Bridged mode operation is
different from the classical single-ended amplifier configura-
tion where one side of the load is connected to ground. A
bridge amplifier design has a few distinct advantages over
the single-ended configuration. It provides a differential drive
to the load, thus doubling output swing for a specified supply
voltage. Four times the output power is possible as com-
pared to a single-ended amplifier under the same conditions.
This increase in attainable output power assumes that the
amplifier is not current limited or clipped. In order to choose
an amplifier’s closed-loop gain without causing excessive
clipping, please refer to the Audio Power Amplifier Design
section.
A bridge configuration, such as the one used in LM4916,
also creates a second advantage over single-ended amplifi-
ers. Since the differential outputs, Vo1 and Vo2, are biased
at half-supply, no net DC voltage exists across the load. This
eliminates the need for an output coupling capacitor which is
required in a single supply, single-ended amplifier configura-
tion.
MODE SELECT DETAIL
The LM4916 can be configured in either Single Ended or
BTL mode (see Figure 2 and Figure 3). The default state of
the LM4916 at power up is single ended. During initial power
up or return from shutdown, the LM4916 must detect the
correct mode of operation by sensing the status of the
SE/BTL pin. When the bias voltage of the part ramps up to
60mV (as seen on the Bypass pin), an internal comparator
detects the status of SE/BTL; and at 10mV, latches that
value in place. Ramp up of the bias voltage will proceed at a
different rate from this point on depending upon operating
mode. BTL mode will ramp up about 11 times faster than
Single Ended mode. Shutdown is not a valid command
during this time period (TWU) and should not enabled to
ensure a proper power on reset (POR) signal. In addition,
the slew rate of VDD must be greater than 2.5V/ms to ensure
reliable POR. Recommended power up timing is shown in
Figure 5 along with proper usage of Shutdown and Mute.
The mode-select circuit is suspended during CB discharge
time. The circuit shown in Figure 4 presents an applications
solution to the problem of using different supply voltages
with different turn-on times in a system with the LM4916.
This circuit shows the LM4916 with a 25-50kΩ. Pull-up re-
sistor connected from the shutdown pin to VDD. The shut-
11 www.national.com
11 Page | ||
| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet LM4916.PDF ] | |
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