Datasheet

Maxim Integrated │ 94
MAX98090 Ultra-Low Power Stereo Audio Codec
www.maximintegrated.com
Table 22. External Gain Mode Series Resistance Values
differential input from IN5 and IN6 (IN6 - IN5). Internally,
all analog signal paths are differential. As a result, single-
ended inputs have a built in baseline gain of +6dB (from
the single-ended to differential conversion) while differen-
tial inputs have 0dB of built in gain.
The line input mixer can also be set to accept and mix
any two single-ended inputs. To facilitate full-scale sig-
nals, when mixing two single-ended inputs an optional
-6dB of attenuation is available (MIXG135 and MIXG246,
Table 23). The line input mixer attenuation setting has
no effect if enabled when only a single input source is
selected. If a differential input to either mixer is enabled,
any single-ended inputs that are also selected are ignored,
and the mixer accepts only the differential input.
Analog Line Input PGAs
To facilitate a wide range of input signal levels, each analog
line input includes a coarse programmable gain amplifier
(PGA) that can provide from 6dB of attenuation to 20dB
of signal gain. The line inputs are then routed to either the
ADC mixer (record) or analog outputs (playback).
If the line input signal exceeds full scale and requires
additional attenuation, the external gain mode provides
trimmed internal feedback resistors (20kΩ) for custom
gain levels. Line input external gain mode is not intended
to provide positive gain, and as such for optimal perfor-
mance any gain of -6dB of higher should be set using the
provided internal PGA gain settings.
Differentially, the external line input gain is set by using
two precision (1% or better), well-matched series input
resistors (Figure 10). Use the following formula to calcu-
late the appropriate differential series input resistors:
A
V_EXTLINE
= 20 x log (20kΩ/R
S_EXT
)
For single-ended inputs, the external line input gain is set
using a single precision (1% or better) series input resis-
tor (Figure 10). However, due to the internal single-ended
to differential conversion, this configuration creates an
unbalanced differential amplifier configuration (configured
external gain paired with a fixed internal gain of +6dB).
Table 22 provides the appropriate series resistance val-
ues for common attenuation settings.
Figure 10. Analog Line Input External Gain Configurations
LINE INPUT
EXTERNAL GAIN (dB)
R
S_EXT
DIFFERENTIAL (kΩ) SINGLE-ENDED (kΩ)
A
V_EXTLINE
= -9.5 60 84.5
A
V_EXTLINE
= -12.0 80 115
A
V_EXTLINE
= -15.0 112 165
A
V_EXTLINE
= -18.0 160 237
R
FB_INT+
= 20kΩ
R
FB_INT-
= 20kΩ
R
S_EXT-
R
S_EXT+
V
IN_DIFF+
V
IN_DIFF-
DIFFERENTIAL LINE INPUT
R
FB_INT+
= 20kΩ
R
FB_INT-
= 30kΩ
R
S_EXT-
= 15kΩ
R
S_EXT+
V
IN_SINGLE-ENDED
V
COMMON_MODE
SINGLE-ENDED LINE INPUT
LINE A
PGA
LINE A
PGA