LM48822TLEVAL National Semiconductor, LM48822TLEVAL Datasheet - Page 10

• Manufacturer Part Number: LM48822TLEVAL
• Description: BOARD EVAL FOR LM48822TL
• Manufacturer: National Semiconductor
• Series: Boomer®r

Specifications of LM48822TLEVAL

• Amplifier Type: Class AB
• Output Type: Headphones, 2-Channel (Stereo)
• Max Output Power X Channels @ Load: 40mW x 2 @ 32 Ohm
• Voltage - Supply: 2.4 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Board Type: Fully Populated
• Utilized Ic / Part: LM48822
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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GENERAL AMPLIFIER FUNCTION
The LM48822 headphone amplifier feature National’s ground
referenced architecture that eliminates the large DC-blocking
capacitors required at the outputs of traditional headphone
amplifiers. A low-noise inverting charge pump creates a neg-
ative supply (CPV
The headphone amplifiers operate from these bipolar sup-
plies, with the amplifier outputs biased about GND, instead of
a nominal DC voltage (typically V
fiers. Because there is no DC component to the headphone
output signals, the large DC-blocking capacitors (typically
220μF) are not necessary, conserving board space and sys-
tem cost, while improving frequency response.
GENERAL AMPLIFIER EXPLANATION
The LM48822 features a differential input stage, which offers
improved noise rejection compared to a single-ended input
amplifier. Because a differential input amplifier amplifies the
difference between the two input signals, any component
common to both signals is cancelled. An additional benefit of
the differential input structure is the possible elimination of the
DC input blocking capacitors. Since the DC component is
common to both inputs, and thus cancelled by the amplifier,
the LM48822 can be used without input coupling capacitors
when configured with a differential input signal.
Device
Address
Register
Address
0
1
Bit
B6
B5
B4
B3
B2
B1
B0
Register
Name
MODE
CONTROL
VOLUME
CONTROL
B7
1
SS
) from the positive supply voltage (V
MUTE_RIGHT
MUTE_LEFT
CP_ONLY
SD_BIAS
UNUSED
B6
Name
1
SDR
SDL
B7
0
1
DD
/2), like traditional ampli-
B5
0
SHDN
SDL
B6
TABLE 3. Mode Control Register
TABLE 2. I
TABLE 1. Device Address
B4
Value
0
0
1
0
1
0
1
0
0
1
0
1
0
1
SD_BIAS
DD
VOL5
2
).
C Control Registers
B5
10
B3
0
Left channel enabled
Left channel disabled
Bias enabled
Bias disabled
Normal operation
Charge-pump only mode. Amplifiers and Bias disabled.
Set B3 to 0
Left channel Normal Operation
Left channel Mute
Right channel enabled
Right channel disabled. Right channel audio inputs summed
with left channel audio inputs and routed to OUTL
Right channel Normal Operation
Right channel Mute
CHARGE PUMP ONLY MODE
In applications where the headphone jack is used as both an
output and input port, signals such as a microphone input can
appear on the headphone amplifier output. Traditional charge
pump headphone amplifiers can clamp or distort the signals
that appear on their output. Without the charge pump active,
generating the negative voltage supply, the internal protection
diodes of the amplifier clamp the incoming signal, distorting
the negative half cycle, see Figure 5. The LM48822 charge
pump only mode eliminates this problem. In charge pump only
mode, the amplifiers are disabled, while the charge pump re-
mains active. The disabled amplifier outputs present a high
impedance (1MΩ) load to the incoming signal. The charge
pump maintains the negative rail, allowing the incoming signal
to swing between V
the device.
Set bit B4 (CP_ONLY) of the MODE CONTROL register to 1
for charge pump only mode. Setting CP_ONLY = 1 disables
both the left and right channels, regardless of the status of the
shutdown control bits. Set CP_ONLY = 0 for normal opera-
tion.
CP_ONLY
VOL4
B4
B2
0
VOL3
B3
0
DD
and V
Description
B1
0
SS
MUTE_
VOL2
LEFT
B2
without any interference from
VOL1
SDR
B1
B0 (R/W)
0
MUTE_
RIGHT
VOL0
B0