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参数资料
| 型号： | LM4919MM/NOPB |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 音频／视频放大 |
| 英文描述： | 0.014 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO10 |
| 封装： | MSOP-10 |
| 文件页数： | 2/15页 |
| 文件大小： | 568K |
| 代理商： | LM4919MM/NOPB |
Application Information
SINGLE ENDED (SE) CONFIGURATION EXPLANATION
As shown in Figure 2, the LM4919 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
A
VD = -(Rf /Ri)
When the LM4919 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 LM4919 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 R
f to
R
iwhile the second amplifier’s gain should be fixed by the
two external 20k
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
A
VD = 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 LM4919,
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 LM4919 can be configured in either Single Ended or
BTL mode (see Figure 2 and Figure 3). The default state of
the LM4919 at power up is single ended. During initial power
up or return from shutdown, the LM4919 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 (T
WU) and should not enabled to
ensure a proper power on reset (POR) signal. In addition,
the slew rate of V
DD 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 C
B 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 LM4919.
This circuit shows the LM4919 with a 25-50k
. Pull-up re-
sistor connected from the shutdown pin to V
DD. The shut-
down pin of the LM4919 is also being driven by an open
drain output of an external microcontroller on a separate
supply. This circuit ensures that shutdown is disabled when
powering up the LM4919 by either allowing shutdown to be
high before the LM4919 powers on (the microcontroller pow-
ers up first) or allows shutdown to ramp up with V
DD (the
LM4919 powers up first). This will ensure the LM4919 pow-
ers up properly and enters the correct mode of operation.
Please note that the SE/BTL pin (Pin 8) should be tied to
GND for Single Ended mode, and to V
DD for BTL mode.
LM4919
www.national.com
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| LM491-SC36 | 功能描述:基本/快动开关 Foot Switch RoHS:否 制造商:Omron Electronics 触点形式:SPDT 执行器:Lever 电流额定值:5 A 电压额定值 AC:250 V 电压额定值 DC:30 V 功率额定值: 工作力:120 g IP 等级:IP 67 NEMA 额定值: 端接类型:Wire 安装:Panel |
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