ꢀ ꢁꢂꢃ ꢄ ꢅ ꢆꢇ ꢈꢉꢉꢅ ꢃ
SLAS356 − DECEMBER 2001
PRINCIPLES OF OPERATION
power-on initialization
An external reset with a minimum pulse width of 500 ns must be applied to the active low RESET terminal to
assure reset upon power on. All registers are set with default values upon external reset initialization.
The desired selection for all programmable functions can be initialized prior to a power-up command using the
2
I C interface.
Table 3. Power-Up and Power-Down Procedures (V
= 2.7 V, Earphone Amplifier Unloaded)
DD
MAXIMUM POWER
CONSUMPTION
DEVICE STATUS
Power up
PROCEDURE
Set bit 1 = 1 in power control register, EAR1 enabled
Set bit 1 = 0 in power control register, EAR2 enabled
Set bit 7 = 1 in TXPGA control register and bit 0 = 0
Set bit 7 = 0 in TXPGA control register and bit 0 = 0
16.2 mW
14.6 mW
1.35 µW
67.5 µW
Power down
In addition to resetting the power-down bit in the power control register, loss of MCLK (no transition detected)
automatically enters the device into a power-down state with PCMO in the high impedance state. If during a
pulse code modulation (PCM) data transmit cycle an asynchronous power down occurs, the PCM interface
remains powered up until the PCM data is completely transferred.
An additional power-down mode overrides the MCLK detection function. This allows the device to enter the
power-down state without regard to MCLK. Setting bit 7 of the TX filter and PGA sidetone register to logic high
enables this function.
conversion laws
The device can be programmed either for a 15-bit linear or 8-bit (µ-law or A-law) companding mode. The
companding operation approximates the CCITT G.711 recommendation. The linear mode operation uses a
15-bit twos-complement format.
transmit operation
microphone input
The microphone input stage is a low-noise differential amplifier that provides a preamplifier gain of 23.5 dB. A
microphone can be capacitively connected to the MIC1N and MIC1P inputs, while the MIC2N and MIC2P inputs
can be used to capacitively connect a second microphone or an auxiliary audio circuit.
21
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