MAX9853 Maxim Integrated Products, MAX9853 Datasheet - Page 36

• Manufacturer Part Number: MAX9853
• Description: (MAX9851 / MAX9853) Stereo Audio CODECs
• Manufacturer: Maxim Integrated Products

Stereo Audio CODECs with Microphone, DirectDrive
Headphones, Speaker Amplifiers, or Line Outputs
Set HRMODE to 100 (register 0x18, bits B2–B0) to
enable standard stereo headphone mode. Set
HRMODE to 110 to configure balanced mono operation
and 101 for single-ended mono operation. When oper-
ating in balanced mode, the right headphone amplifier
is reconfigured as a slave amplifier to create a bridge-
tied load output. In single-ended mono mode, only the
left headphone amplifier is used. Both mono modes
output the sum of the left- and right-channel audio.
Set HRMODE to 111 to disable the headphone amplifi-
er and enable the mono receiver amplifier. The receiver
amplifier outputs a sum of the left and right headphone
signals to provide 100mW to a telephone earpiece
speaker.
The headphone/receiver amplifiers have programmable
gain controlled by HRVOLL and HRVOLR (registers
0x14 and 0x15). The independent gain control offers a
range of +5.5dB to -74dB.
36
Figure 5. Traditional Amplifier Output vs. MAX9851/MAX9853
DirectDrive Output
CONVENTIONAL AMPLIFIER BIASING SCHEME
DirectDrive AMPLIFIER BIASING SCHEME
______________________________________________________________________________________
V
GND
+V
SGND
-V
V
DD
DD
DD
DD
/ 2
Set SPMODE to 11 (register 0x18, bits B4 and B3) to
enable the stereo speaker amplifier of the MAX9851.
SPMODE can be optionally set to enable just the left or
the right speaker. CPCLK (register 0x1A, bit B0) must
be set to 1 to ensure proper Class D amplifier opera-
tion. The Class D amplifier oscillator is derived from
MCLK. MCLK must be enabled for proper Class D
amplifier operation.
The on-board filterless, low-EMI, Class D audio power
amplifier offers Class AB performance with Class D effi-
ciency. The amplifiers are powered directly from the
battery (PV
put. A typical output power of up to 2W per channel
allows powering of internal speakers without the need
for a separate power amplifier IC. The Class D amplifier
has been optimized for efficiency and greatly reduced
EMI. The output gain is adjustable between +13.1dB
and -66.4dB. The gain of the speaker amplifier is con-
trolled with SPVOLL and SPVOLR (registers 0x16 and
0x17, bits B0–B5).
Rather than using a traditional Class AB speaker amplifi-
er, the MAX9851 uses a high-efficiency Class D audio
amplifier to provide speaker outputs. The MAX9851 uses
Maxim’s unique, patented modulation scheme that elimi-
nates the LC filter required by standard Class D ampli-
fiers, improving efficiency, reducing component count,
and conserving board space and system cost.
Conventional Class D amplifiers output a 50% duty-cycle
square wave when no signal is present. With no filter, the
square wave appears across the load as a DC voltage,
resulting in finite load current, increasing power con-
sumption. When no signal is present at the input of the
MAX9851, the outputs switch in-phase at a low duty
cycle. Because the MAX9851 drives the speaker differ-
entially, the two outputs cancel, resulting in no net volt-
age across the speaker, minimizing power consumption.
Proprietary active emissions limiting (AEL) output stage
circuitry allows the amplifier to operate at switching fre-
quencies above 1MHz while still providing at least
20dB margin below FCC-radiated emissions limits. Set
CPCLK = 1 (register 0x1A, bit B0) to configure the
Class D amplifier to operate with a 1.1MHz MCLK
derived switching frequency. The MAX9851 does not
require an output filter, instead relying on the inherent
DD
) for maximum efficiency and power out-
Class D Speaker Amplifiers
Filterless Operation
(MAX9851 Only)
Efficiency