TCM320AC56 Datasheet, PDF (13/23 Pages) Texas Instruments – VOICE-BAND AUDIO PROCESSORS (VBAP)

TCM320AC56, TCM320AC57
VOICE-BAND AUDIO PROCESSORS (VBAP)
PRINCIPLES OF OPERATION
SLWS016A – JUNE 1996 – REVISED APRIL 1997
general
system reliability features
The device should be powered up and initialized as follows:
1. Apply GND.
2. Apply V_CC.
3. Connect all clocks.
4. Apply TTL high to PDN.
5. Apply synchronizing pulses to FSX and/or FSR.
Even though the VBAP is heavily protected against latch-up, it is still possible to cause it to latch up under certain
improper power conditions. To help ensure that latch-up does not occur, a reverse-biased Schottky diode with
a forward voltage drop of less than or equal to 0.4 V (1N5711 or equivalent) should be connected between V_CC
(power supply) and GND.
On the transmit channel, digital outputs DOUT and TSX are held in the high-impedance state for approximately
four frames (500 µs) after power up or application of V_CC. After this delay, DOUT, TSX, and signaling are
functional and occur in the correct time slot. The analog circuits on the transmit side require approximately
60 ms to reach their equilibrium value due to the autozero circuit settling time. To further enhance system
integrity, DOUT and TSX are placed in the high-impedance state after an interruption of CLK.
power-down and standby operations
To minimize power consumption, a power-down mode and three standby modes are provided.
For power down, an external low signal is applied to PDN. In the absence of a signal, PDN is internally pulled
up to a high logic level and the device remains active. In the power-down mode, the average power consumption
is reduced to 3 mW.
Three standby modes give the user the option of placing the entire device on standby, placing only the transmit
channel on standby, or placing only the receive channel on standby. To place the entire device on standby, both
FSX and FSR are held low. For transmit-only operation (receive channel on standby), FSX is pulsing and FSR
is held low. For receive-only operation (transmit section on standby), FSR is pulsing and FSX is held low. When
the entire device is in standby mode, power consumption is reduced to 5 mW. See Table 1 for power-down and
standby procedures.
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