參數(shù)資料
型號(hào)： LM4835MDC
廠商： NATIONAL SEMICONDUCTOR CORP
元件分類： 音頻控制
英文描述： 2 CHANNEL(S), VOLUME CONTROL CIRCUIT, UUC
封裝： DIE
文件頁(yè)數(shù)： 6/26頁(yè)
文件大?。?/td> 858K
代理商： LM4835MDC
Application Information (Continued)
nected to the output amplifiers. A valid beep signal will be
applied to the load even when MUTE is active. Use the input
resistors connected between the BEEP IN pin and the stereo
input pins to accommodate different beep signal amplitudes.
These resistors are shown as 200k
devices in Figure 2.
Use higher value resistors to reduce the gain applied to the
beep signal. The resistors must be used to pass the beep
signal to the stereo inputs. The BEEP IN pin is used only to
detect the beep signal’s magnitude: it does not pass the
signal to the output amplifiers. The LM4835’s shutdown
mode must be deactivated before a system alert signal is
applied to BEEP IN pin.
MICRO-POWER SHUTDOWN
The voltage applied to the SHUTDOWN pin controls the
LM4835’s shutdown function. Activate micro-power shut-
down by applying V
DD to the SHUTDOWN pin. When active,
the LM4835’s micro-power shutdown feature turns off the
amplifier’s bias circuitry, reducing the supply current. The
logic threshold is typically V
DD/2. The low 0.7 A typical
shutdown current is achieved by applying a voltage that is as
near as V
DD as possible to the SHUTDOWN pin. A voltage
that is less than V
DD may increase the shutdown current.
Table 1 shows the logic signal levels that activate and deac-
tivate micro-power shutdown and headphone amplifier op-
eration.
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 10k
pull-up resistor between the
SHUTDOWN pin and V
DD. Connect the switch between the
SHUTDOWN pin and ground. Select normal amplifier opera-
tion by closing the switch. Opening the switch connects the
SHUTDOWN pin to V
DD through the pull-up resistor, activat-
ing micro-power shutdown. The switch and resistor guaran-
tee 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 for SHUTDOWN, HP-IN, and MUX Operation
SHUTDOWN
PIN
HP-IN PIN
MUX CHANNEL
SELECT PIN
OPERATIONAL MODE
(MUX INPUT CHANNEL #)
Logic Low
Bridged Amplifiers (1)
Logic Low
Logic High
Bridged Amplifiers (2)
Logic Low
Logic High
Logic Low
Single-Ended Amplifiers (1)
Logic Low
Logic High
Single-Ended Amplifiers (2)
Logic High
X
Micro-Power Shutdown
MODE FUNCTION
The LM4835’s MODE function has two states controlled by
the voltage applied to the MODE pin (pin 4). Mode 0, se-
lected by applying 0V to the MODE pin, forces the LM4835
to effectively function as a ’line-out,’ unity-gain amplifier.
Mode 1, which uses the internal DC controlled volume con-
trol, is selected by applying V
DD to the MODE pin. This mode
sets the amplifier’s gain according to the DC voltage applied
to the DC VOL CONTROL pin. Prevent unanticipated gain
behavior by connecting the MODE pin to V
DD or ground. Do
not let pin 4 float.
MUTE FUNCTION
The LM4835 mutes the amplifier and DOCK outputs when
V
DD is applied to pin 5, the MUTE pin. Even while muted, the
LM4835 will amplify a system alert (beep) signal whose
magnitude satisfies the BEEP DETECT circuitry. Applying
0V to the MUTE pin returns the LM4835 to normal, unmated
operation. Prevent unanticipated mute behavior by connect-
ing the MUTE pin to V
DD or ground. Do not let pin 5 float.
HP-IN FUNCTION
Applying a voltage between 4V and V
DD to the LM4835’s
HP-IN headphone control pin turns off Amp2A and Amp2B,
muting a bridged-connected load. Quiescent current con-
sumption is reduced when the IC is in this single-ended
mode.
DS100139-4
FIGURE 4. Headphone Sensing Circuit
LM4835
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