Datasheet
MAX9850
where:
f
ICLK
= ICLK frequency. f
ICLK
must be at least 176 x
f
LRCLK
for proper DAC operation.
f
LRCLK
= LRCLK frequency.
N
MSB,LSB
= decimal value of MSB(14:8) and LSB(7:0)
(register 0x8, bits B6–B0 and register 0x9, bits B7–B0).
Round the results of the equation to the nearest integer
value.
For example:
f
LRCLK
= 44.1kHz, f
ICLK
= 12.288MHz.
1) Solve for N
MSB,LSB
, 15052.8.
2) Round result to nearest integer value. 15053.
3) Convert to hex, 0x3CD.
4) Program MSB(14:8) with the MSB 0x3A and program
LSB(7:0) with the LSB 0xCD).
Table 7 provides examples of using master noninteger
mode with various MCLK frequencies to generate useful
LRCLK frequencies.
Charge Pump
The DirectDrive line and headphone outputs of the
MAX9850 require a charge pump to create the internal
negative power supply. Set CPEN(1:0) = 11 in the
enable register (register 0x5, bits B5 and B4) to turn on
the charge pump. The negative charge-pump voltage
is established and the audio outputs are ready for use
approximately 1.4ms after CPEN is set to 11.
The state of CP(4:0), in the charge-pump register (register
0x7, bits B4–B0), determines whether the charge-pump
oscillator is derived from the internal 667kHz oscillator or
from MCLK. Set CPEN(1:0) = 11 and set CP(4:0) = 0x00
to enable the internal oscillator. The charge pump runs
independent from MCLK when the internal oscillator is
enabled allowing the charge pump to operate when the
DAC is disabled or when only the line inputs are used. No
MCLK is required when only the line inputs are used.
The switching frequency of the charge pump is well
beyond the audio range and does not interfere with audio
signals. The switch drivers utilize techniques that mini-
mize noise generated by turn-on and turn-off transients.
Although not typically required, additional high-frequency
noise attenuation can be achieved by increasing the size
of C2 and the PV
DD
bypass capacitor (see the Functional
Diagram/Typical Operating Circuit).
Derive the charge-pump clock from MCLK by program-
ming CP(4:0) to a non-zero value based on the following
equation:
where:
f
MCLK
= MCLK frequency.
f
CP
= charge-pump clock frequency. Ensure f
CP
=
667kHz ±20% for proper operation.
SF = MCLK scale factor. SF is the decimal value of
IC(1:0) + 1.
N
CP(4:0)
= rounded decimal value of CP(4:0) (register
0x7, bits B4–B0). N
CP(4:0)
must be greater than 1 when
deriving the charge-pump clock from I
CLK
.
N
f
fSF
CP
MCLK
CP
(:)
40
2
=
××
Stereo Audio DAC with DirectDrive
Headphone Amplifier
20 ______________________________________________________________________________________
Table 7. Master Noninteger N
MSB,LSB
Examples
N (15-BIT hex VALUE)
LRCLK OUTPUT FREQUENCY (kHz)
MCLK
(MHz)
SF
ICLK
(MHz)
48 44.1 32 24
22.05
16 12
11.03
8
18.4320
2
9.2160
5555 4E66 38E4
2AAB
2733 1C72 1555 139A 0E39
16.9344
2
8.4672 5CE1
5555
3DEB
2E71
2AAB
1EF6 1738 1555 0F7B
16.3840
2
8.1920
5833 4000 3000
2C1A
2000 1800 160D 1000
12.5000
1
12.5000 3EEA
39CE 29F1 1F75
1CE7
14F9 0FBB 0E73
0A7C
12.2880
1
12.2880
4000
3ACD 2AAB
2000 1D66 1555 1000 0EB3
0AAB
12.0000
1
12.0000
4189 3C36
2BB1
20C5 1E1B 15D8 1062 0F0E
0AEC
11.2896
1
11.2896
45A9 4000 2E71 22D4 2000 1738 116A 1000
0B9C
9.2160
1
9.2160
5555 4E66 38E4
2AAB
2733 1C72 1555 139A 0E39
8.4672
1
8.4672 5CE1
5555
3DEB
2E71
2AAB
1EF6 1738 1555 0F7B
8.4480
1
8.4480
5D17 5587 3E10 2E8C
2AC3
1F08 1746 1562 0F84
Note: The N values represent the combined MSB(14:8) and LSB(7:0) values.