ISD3900
Publication Release Date: Dec 10, 2013
- 16 -
Revision 1.5
Analog outputs consist of:
AUXOUT is a single-ended voltage output
AUDOUT can be configured as a single-ended voltage output or a single-ended current
output. When configured as a voltage output, AUDOUT is exactly the same as the
AUXOUT.
BTL (bridge-tied-load) is a differential voltage output, which shares the same two pins of
PWM (SPK+/SPK-). Signal source of BTL could be either from AUD_MUX or AUX_MUX.
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Besides BTL, SPK+ and/or SPK- can also be configured individually:
SPK+ can switch to AUDOUT or AUXOUT
SPK- can switch to AUDOUT or AUXOUT
The analog path consists of the following blocks: AUXIN, ANAIN (or MICIN), SUM1, ADC_MUX
(SUM1 and ADC_MUX are ineffective when MICIN is selected), SUM2, SUM2_MUX, AUD_MUX,
AUX_MUX, SPK+_MUX, and SPK-_MUX. The summation blocks, SUM1 and SUM2, are able to mix
two signals together. SUM1 mixes the two analog inputs (AUXIN and ANAIN) for input into the digital
signal path. SUM2 mixes the analog input (AUXIN, or ANAIN, or AUXIN plus ANAIN) with the digital
signal path output. ADC_MUX provides input selection into the ADC. AUD_MUX and AUX_MUX
provide input selection into the AUDOUT and AUXOUT blocks. SPK+_MUX and SPK-_MUX provide
input selection into the SPK+ and SPK- blocks. The configuration registers, CFG5-CFG9 & CFG18,
control the active path features, allow individual power control of each block and enable the muting of
certain path inputs. The details of the path configuration registers are described in Section 12.3.
7.1.1
ANAIN & MICIN Analog Input
Single-ended ANAIN Input
ANAIN
ANAOUT
ANAIN
1V
pp
Vin
coup
C
in
R
f
R
Figure 7-3 ANAIN Input Amplifier
The ANAIN input amplifier is designed to allow a variable gain set via two external resistors. The goal
of gain selection is to produce a
pp
V
1
signal into the ISD3900 audio path. Voltage gain is: