TLC32044C, TLC32044E, TLC32044I, TLC32044M, TLC32045C, TLC32045I

VOICE-BAND ANALOG INTERFACE CIRCUITS

SLAS017F − MARCH 1988 − REVISED MAY 1995

8

POST OFFICE BOX 655303

PRINCIPLES OF OPERATION

operation of TLC32044 or TLC32045 with internal voltage reference

The internal reference eliminates the need for an external voltage reference and provides overall circuit cost

reduction. Thus, the internal reference eases the design task and provides complete control over device

performance. The internal reference is brought out to a terminal and is available to the designer. To keep the

amount of noise on the reference signal to a minimum, an external capacitor can be connected between REF

and ANLG GND.

operation of TLC32044 or TLC32045 with external voltage reference

REF can be driven from an external reference circuit. This external circuit must be capable of supplying

250

µA and must be adequately protected from noise such as crosstalk from the analog input.

reset

A reset function is provided to initiate serial communications between the AIC and DSP and to allow fast,

cost-effective testing during manufacturing. The reset function initializes all AIC registers, including the control

register. After a negative-going pulse on RESET, the AIC is initialized. This initialization allows normal serial port

communications activity to occur between AIC and DSP (see AIC DX data word format section).

loopback

This feature allows the user to test the circuit remotely. In loopback, OUT + and OUT− are internally connected

to the IN+ and IN−. Thus, the DAC bits (d15 to d2), which are transmitted to DX, can be compared with the ADC

bits (d15 to d2), which are received from DR. An ideal comparison would be that the bits on DR equal the bits

on DX. However, there are some difference in these bits due to the ADC and DAC output offsets. The loopback

feature is implemented with digital signal processor control by transmitting the appropriate serial port bit to the

control register (see AIC DX data word format section).