TLC320AD56C Datasheet, PDF (18/43 Pages) Texas Instruments – Sigma-Delta Analog Interface Circuit

2.2.6 Frame-Sync Function
The frame-sync signal indicates that the device is ready to send and receive data. The data transfer from
DOUT and into DIN begins on the falling edge of the frame-sync signal.
The frame sync is generated internally and goes low on the rising edge of SCLK and remains low during
the 16-bit data transfer.
2.2.7 Multiplexed Analog Input
The two differential analog inputs (INP and INM or AUXP and AUXM) are multiplexed into the sigma-delta
modulator. The performance of the AUX channel is similar to the normal input channel. A simple RC
antialiasing filter must be connected to AUXP and AUXM (also INP and INM when used).
PWRDWN
Digital Circuitry
Power Down
Analog Circuitry
Power Down
Clear
(For Control
Reg. 1, Bit 6)
Bit 6 is Programmed
Through a Secondary
Write Operation
Internal TLC320AD56C
Figure 2–1. Internal Power-Down Logic
2.2.8 Analog Input
The signal applied to the terminals INM and INP (shown in Figure 2–2) should be differential to preserve
the device specifications. A single-ended input signal should always be converted to a differential input
signal prior to being used by the TLC320AD56C (see section 5 Application Information). The signal source
driving the analog inputs (INM, INP, AUXM, AUXP) should have a low source impedance for lowest noise
performance and accuracy. To obtain maximum dynamic range, the input signal should be centered at
midsupply. A simple RC antialiasing filter must be connected to INP and INM (also AUXP and AUXM if used).
A suitable tradeoff for the cutoff frequency (f_co) of the antialiasing filter is f_co = 3 x f_s. With this cutoff frequency,
the attenuation within the band of interest (0 – f_s/2) is less than 0.1 dB.
2.2.9 Analog Output
The analog output swing across the OUTP and OUTM terminals depends on the value of the resistor used
from the IGAIN terminal to analog ground and the resistor load across the OUTP and OUTM terminals. Both
resistors can be used to set the output voltage swing and then gained to the desired value in the external
DAC output filter as shown in Figure 5–1 and Figure 5–2. With this external filter, the gain of the DAC channel
is –2.5 dB.
The resistor on the IGAIN terminal sets up the output current pumped and the resistor across OUTP and
OUTM is the load which converts the current output of the DAC to a voltage. Hence, the voltage swing across
OUTP and OUTM depends on the ratio of the load resistor to the value of the resistor from the IGAIN terminal
to analog ground. With 0 dB digital code applied to the DAC channel, the IGAIN resistor set at 27 kΩ, and
a load resistor of 5 kΩ, the output swing across OUTP and OUTM is –10.5 dB. The ratio of IGAIN resistance
to load resistance can be adjusted to get the desired voltage swing. For the best distortion performance,
it is recommended that the output swing be limited to –6 dB relative to 6 V_PP.
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