TLC320AD90C Datasheet, PDF (32/51 Pages) Texas Instruments – Stereo Audio Codec

2.6 Microphone Input Programmable Gain Amplifier
The TLC320AD90C is designed to allow most common microphones to be connected to it without the use
of external preamplifiers. As shown in Figure 2–7, the microphone input multiplexer is followed by a buffer
amplifier with 100-kΩ input impedance. This configuration allows the value of the input coupling capacitors
to be kept small while maintaining acceptable low frequency response characteristics.
A bias voltage through two 100-kΩ resistors is maintained on both MIC1 and MIC2 to allow for rapid
switching between the two microphones.
As shown in Figure 2–7, the reference output is designed to provide bias current for two microphones.
Figure 2–7 shows the connection of two electret microphones to the TLC320AD90C codec.
TLC320AD90C
50 Ω
REFOUT
Buffer
2.2 kΩ
2.2 kΩ
MIC1 ^{0.1 µF}
Output From MIC1
M
U
X
MIC2
Output From MIC2
–
0.1 µF
+
100 kΩ
100 kΩ
Vref
Figure 2–7. Microphone Programmable Gain Amplifier With Two Electret Microphones
2.7 Power-Down Management
The TLC320AD90C is capable of operating at reduced power when no activity is required. The state of
power down is controlled by the Power Down register (Index 26h). There are seven commands of separate
power down with the addition of modem codec. The TLC320AD90C is fully static and if the clock is stopped,
the register values are not lost. Table 2–15 lists the different power-down modes.
Table 2–15. Power-Down Modes
BITS
PR0
PR1
PR2
PR3
PR4
PR5
FUNCTION
PCM in ADCs and input MUX power down
PCM out DACs power down
Analog mixer power down (Vref on)
Analog mixer power down (Vref off)
Digital interface (AC‘97) power down (external clock off)
Internal clock disabled
2–18