LM4937RL/NOPB National Semiconductor, LM4937RL/NOPB Datasheet - Page 23

• Manufacturer Part Number: LM4937RL/NOPB
• Description: IC AUDIO SUBSYSTM 1.25W 36USMDXT
• Manufacturer: National Semiconductor
• Series: Boomer®r
• Type: Class ABr

Specifications of LM4937RL/NOPB

• Output Type: 1-Channel (Mono) with Mono and Stereo Headphones
• Max Output Power X Channels @ Load: 1.25W x 1 @ 8 Ohm; 80mW x 2 @ 32 Ohm
• Voltage - Supply: 2.7 V ~ 5.5 V
• Features: Depop, Differential Inputs, I²C, I²S, Mute, Shutdown, SPI, Volume Control
• Mounting Type: Surface Mount
• Package / Case: 36-MicroSMDxt
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM4937RLTR

Common Clock Settings for the DAC
The DAC can work in 4 modes, each with different oversampling rates, 125,128,64 & 32. In normal operation 125x oversampling
provides for the simplest clocking solution as it will work from 12.000MHz (common in most systems with Bluetooth or USB) at
48kHz exactly. The other modes are useful if data is being provided to the DAC from an uncontrollable isochronous source (such
as a CD player, DAB, or other external digital source) rather than being decoded from memory. In this case the PLL can be used
to derive a clock for the DAC from the I2S clock.
The DAC oversampling rate can be changed to allow simpler clocking strategies, this is controlled in the DAC SETUP register but
the oversampling rates are as follows:
The following table describes the clock required at the clock generator input for various clock sample rates in the different DAC
modes:
Methods for producing these clock frequencies are described in the PLL section.
The R divider can be used when the master clock is exactly 12.00 MHz in order to generate different sample rates. The Table
below shows different sample rates supported from 12.00MHz by using only the R divider and disabling the PLL. In this way we
can save power and the clock jitter will be low.
R_DIV
Fs (kHz)
11.025
11.025
11
22.05
22.05
176.4
9
7
5
4
44.1
44.1
88.2
192
12
12
16
16
24
24
32
32
48
48
96
8
8
Divide Value
DAC MODE
2.5
6
5
4
3
DAC Oversampling Ratio
00
01
10
11
125
128
125
128
125
128
125
128
125
128
125
128
125
128
125
128
125
128
64
64
32
32
DAC Clock Generator Input Frequency <MHz>
2.4
4.8
2
3
4
Required CLock at DAC Clock Generator Input (MHz)
23
Over sampling Ratio Used
125
128
64
32
2.75625
11.2896
11.2896
22.5792
2.8224
5.5125
5.6448
11.025
12.288
12.288
24.576
2.048
3.072
4.096
6.144
8.192
12
2
3
4
6
8
Sample Rate Supported <KHz>
19.2
9.6
12
16
8
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