TCM320AC36, TCM320AC37

VOICE-BAND AUDIO PROCESSORS (VBAP

™)

SLWS003C – MAY 1992 – REVISED APRIL – 1998

13

POST OFFICE BOX 655303

PRINCIPLES OF OPERATION

general

system reliability features

The device should be powered up and initialized as follows:

1.

Apply GND.

2.

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

On the transmit channel, digital outputs DOUT and TSX are held in the high-impedance state for approximately

four frames (500

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.