Datasheet

LM49350, LM49350RLEVAL
SNAS359D –SEPTEMBER 2008–REVISED JUNE 2012 www.ti.com
CHARGE PUMP FLYING CAPACITOR (C6)
The flying capacitor (C6) affects the load regulation and output impedance of the charge pump. A C6 value that
is too low results in a loss of current drive, leading to a loss of amplifier headroom. A higher valued C6 improves
load regulation and lowers charge pump output impedance to an extent. Above 2.2μF, the R
DS(ON)
of the charge
pump switches and the ESR of C6 and C5 dominate the output impedance. A lower value capacitor can be used
in systems with low maximum output power requirements. Please refer to the demonstration board schematic
shown in Schematic Diagram.
CHARGE PUMP FLYING CAPACITOR (C5)
The value and ESR of the hold capacitor (C5) directly affects the ripple on CPV
SS
. Increasing the value of C5
reduces output ripple. Decreasing the ESR of C5 reduces both output ripple and charge pump output impedance.
A lower value capacitor can be used in systems with low maximum output power requirements. Please refer to
the demonstration board schematic shown in Schematic Diagram.
Table 21. AUX_OUTPUT (0x13h)
Bits Field Description
0 DACR_AUX The right DAC output is added to the AUX output.
1 DACL_AUX The left DAC output is added to the AUX output.
2 MICR_AUX The right MIC input is added to the AUX output. Setting this bit enables the MIC BIAS output.
3 MICL_AUX The left MIC input is added to the AUX output. Setting this bit enables the MIC BIAS output.
4 AUXR_AUX The right AUX input is added to the AUX output.
5 AUXL_AUX The left AUX input is added to the AUX output.
AUXILIARY OUTPUT AMPLIFIER
The LM49350’s auxiliary output (AUXOUT) amplifier provides differential drive capability to loads that are
connected across its outputs. This results in output signals at the AUX_OUT+ and AUX_OUT- pins that are 180
degrees out of phase with respect to each other. This effectively doubles the maximum possible output swing for
a specific supply voltage when compared to single-ended output configurations. The differential output
configuration also allows the load to be isolated from ground since both the AUX_OUT+ and AUX_OUT- pins are
biased at the same DC potential. This eliminates the need for any large and expensive DC blocking capacitors at
the AUXOUT amplifier outputs. The load can then be directly connected to the positive and negative outputs of
the AUXOUT amplifier which then isolates it from any ground noise, thereby improving signal to noise ratio
(SNR) and power supply rejection ratio (PSRR).
The AUXOUT amplifier has two modes of operation. The primary mode of operation is high current drive mode
(Earpiece Mode) where the AUXOUT amplifier can be used to differentially drive a mono earpiece speaker. The
secondary mode of operation is low current drive mode where the AUXOUT amplifier operates in a power saving
mode (AUX_LINE_OUT Mode) to provide a differential output that is used as a mono differential line level input
to a standalone mono differential input class D amplifier (LM4675) for stereo loudspeaker applications.
Table 22. OUTPUT_OPTIONS (0x14h)
Bits Field Description
0 EPMODE If set the HPR output is driven with the negative input of the HPL output stage.
If set, both HPL and HPR are attenuated by 6dB. This is useful when adding stereo signals
1 HP_NEG_6dB
that need more headroom due to being highly correlated.
If set the class D output is attenuated by 6dB. This is useful when adding stereo signals that
2 LS_NEG_6dB
need more headroom due to being highly correlated.
If set the AUX output is attenuated by 6dB. This is useful when adding stereo signals that
3 AUX_NEG_6dB
need more headroom due to being highly correlated.
4 CP_FORCE If set, a -LS_VDD rail will be created on HP_VSS, even if the HP output stage is not required.
42 Submit Documentation Feedback Copyright © 2008–2012, Texas Instruments Incorporated
Product Folder Links: LM49350 LM49350RLEVAL