TCM29C23_12 Datasheet, PDF (16/20 Pages) Texas Instruments – VARIABLE-FREQUENCY PCM OR DSP INTERFACE

TCM29C23, TCM129C23
VARIABLE-FREQUENCY PCM OR DSP INTERFACE
SCTS029B − AUGUST 1989 − REVISED NOVEMBER 1996
PRINCIPLES OF OPERATION
V_CC
DGND
V_BB
Figure 7. Latch-Up Protection Diode Connection
internal sequencing
On the transmit channel, digital outputs PCM OUT and TSX are held in the high-impedance state for
approximately four frames (500 μs) after power up or application of V_{BB or} V_CC. After this delay, PCM OUT, TSX,
and signaling are functional and occur in the proper 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. Thus valid digital
information, such as on/off hook detection, is available almost immediately while analog information is available
after some delay. To further enhance system reliability, PCM OUT and TSX are placed in the high-impedance
state approximately 20 μs after an interruption of CLKX.
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 interally pulled
up to a high logic level and the device remains active. In the power-down mode, the average power consumption
is reduced to 5 mW.
Three standby modes give the user the options 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 high and FSR is
held low. For receive-only operation (transmit section on standby), FSR is high and FSX is held low. When the
entire device is in standby mode, power consumption is reduced to an average of 3 mW (see Table 1).
Table 1. Power-Down and Standby Procedures
DEVICE STATUS
PROCEDURE
Power down
PDN low
Entire device on standby FSX and FSR are low
Only transmit on standby FSX is low, FSR is high
Only receive on standby FSR is low, FSX is high
TYPICAL POWER
CONSUMPTION
3 mW
3 mW
40 mW
30 mW
DIGITAL OUTPUT STATUS
TSX and PCM OUT are in the high-impedance state; SIGR
goes to low within 10 μs.
TSX and PCM OUT are in the high-impedance state; SIGR
goes to low within 300 ms.
TSX and PCM OUT are placed in the high-impedance state
within 300 ms.
SIGR is placed in the high-impedance state within 300 ms.
16
• POST OFFICE BOX 655303 DALLAS, TEXAS 75265