LM4936MH National Semiconductor, LM4936MH Datasheet - Page 20

• Manufacturer Part Number: LM4936MH
• Description: IC,Audio Amplifier,DUAL,TSSOP,28PIN,PLASTIC
• Manufacturer: National Semiconductor

Specifications of LM4936MH

• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

www.national.com
Application Information
DOCKING STATION INTERFACE
Applications such as notebook computers can take advan-
tage of a docking station to connect to external devices such
as monitors or audio/visual equipment that sends or receives
line level signals. The LM4936 has two outputs, Right Dock
and Left Dock, which connect to outputs of the internal input
amplifiers that drive the volume control inputs. These input
amplifiers can drive loads of
ers) with a rail-to-rail signal. Since the output signal present
on the RIGHT DOCK and LEFT DOCK pins is biased to
V
with the load when using these outputs. Typical values for
the output coupling capacitors are 0.33µF to 1.0µF. If polar-
ized coupling capacitors are used, connect their "+" termi-
nals to the respective output pin, see Figure 2.
Since the DOCK outputs precede the internal volume con-
trol, the signal amplitude will be equal to the input signal’s
magnitude and cannot be adjusted. However, the input am-
plifier’s closed-loop gain can be adjusted using external
resistors. These 20kΩ (R
ure 2 and they set each input amplifier’s gain to -1. Use
Equation 8 to determine the input and feedback resistor
values for a desired gain.
Adjusting the input amplifier’s gain sets the minimum gain for
that channel. Although the single ended output of the Bridge
Output Amplifiers can be used to drive line level outputs, it is
recommended that the R & L Dock Outputs simpler signal
path be used for better performance.
BEEP DETECT FUNCTION
Computers and notebooks produce a system “beep“ signal
that drives a small speaker. The speaker’s auditory output
signifies that the system requires user attention or input. To
accommodate this system alert signal, the LM4936’s beep
input pin is a mono input that accepts the beep signal.
Internal level detection circuitry at this input monitors the
beep signal’s magnitude. When a signal level greater than
V
amplifiers are enabled. The beep signal is amplified and
applied to the load connected 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 (R
as 200kΩ values 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 amplifi-
ers. The LM4936’s shutdown mode must be deactivated
before a system alert signal is applied to BEEP IN pin.
DD
DD
/2, coupling capacitors should be connected in series
/2 is detected on the BEEP IN pin, the bridge output
- A
VR
= R
DOCK1
C
0.01µF
0.22µF
0.47µF
/R
0.1µF
1.0µF
B
IN1
DOCK1
and - A
>
1kΩ (such as powered speak-
, R
T
DOCK2
200ms
ON
VL
20ms
44ms
94ms
2ms
= R
) are shown in Fig-
DOCK2
(Continued)
BEEP
) are shown
/R
IN2
(8)
20
MICRO-POWER SHUTDOWN
Shutdown mode is activated when a digital 0 is loaded into
the Shutdown bit, B0. When active, the LM4936’s micro-
power shutdown feature turns off the amplifier’s bias circuitry
reducing supply current to a typical 0.7µA. Loading a digital
1 into B0 disables shutdown mode. When the LM4936 has
power applied, all register bits will have a default value of 0.
Because of this, the LM4936 will be in shutdown mode when
power is applied.
MODE FUNCTION
The LM4936’s Mode function has two states controlled by bit
B2. A digital 0 in bit B2 disables the volume control and
forces the LM4936 to function as a fixed gain amplifier. The
gain selection is determined by the GAIN SEL bit (B3) While
in the fixed gain mode the volume setting has no effect on
the output. When a digital 1 is loaded into B2 the output level
is determined by the volume control bits. See Table 4 for
volume settings.
MUTE FUNCTION
The LM4936 mutes the amplifier and DOCK outputs when a
digital 1 is loaded in bit B1. Even while muted, the LM4936
will amplify a system alert (beep) signal whose magnitude
satisfies the BEEP DETECT circuitry. Loading a digital 0 into
B1 returns the LM4936 to normal operation.
HP SENSE FUNCTION ( Headphone In )
Applying a voltage between the V
graph found in the Typical Performance Characteristics and
V
digital 1 into the HP Control bit (B4) will change the output
mode. The ’+’ outputs will change to be in phase with the ’-’
outputs instead of 180 degrees out of phase. This action
mutes a bridged-connected load since the differential volt-
age across the load is now close to 0V. The HP SENSE pin
over rides the HP Control bit. See Table 2 for more info.
Quiescent current consumption is reduced when the IC is in
this single-ended mode.
Figure 3 shows the implementation of the LM4936’s head-
phone control function. With no headphones connected to
the headphone jack, the R1-R2 voltage divider sets the
DD
to the LM4936’s HP SENSE control pin or loading a
FIGURE 3. Headphone Sensing Circuit
IH
threshold shown in the
20117805