TLC3544_07 Datasheet, PDF (14/42 Pages) Texas Instruments – 5-V ANALOG, 3-/5-V DIGITAL, 14-BIT, 200-KSPS, 4-/8-CHANNELS SERIAL ANALOG-TO-DIGITAL CONVERTERS WITH 0-5 V (PSEUDODIFFERENTIAL) INPUTS

TLC3544, TLC3548
5-V ANALOG, 3-/5-V DIGITAL, 14-BIT, 200-KSPS, 4-/8-CHANNELS SERIAL
ANALOG-TO-DIGITAL CONVERTERS WITH 0-5 V (PSEUDODIFFERENTIAL) INPUTS
SLAS266C – OCTOBER 2000 – REVISED MAY 2003
detailed description (continued)
Charge
Redistribution
DAC
Ain
_
+
Control
Logic
ADC Code
REFM
Figure 5. Simplified Block Diagram of the Successive-Approximation System
analog input range and internal test voltages
TLC3548 has eight analog inputs (TLC3544 has four) and three test voltages. The inputs are selected by the
analog multiplexer according to the command entered (see Table 1). The input multiplexer is a break-
before-make type to reduce input-to-input noise injection resulting from channel switching.
The TLC3544 and TLC3548 are specified for a unipolar input range of 0-V to 4-V when the internal reference
is selected, and 0-V to 5-V when an external 5-V reference is used.
analog input mode
Two input signal modes can be selected: single-ended input and pseudodifferential input.
Charge
Redistribution
DAC
S1
Ain(+)
Ain(–)
_
Control
+
Logic
ADC Code
REFM
When sampling, S1 is closed and S2 connects to Ain(–).
During conversion, S1 is open and S2 connects to REFM.
Figure 6. Simplified Pseudodifferential Input Circuit
Pseudodifferential input refers to the negative input, Ain(–); its voltage is limited in magnitude to ±0.2 V. The input
frequency limit of Ain(–) is the same as the positive input Ain(+). This mode is normally used for ground noise
rejection or dc bias offset.
When pseudodifferential mode is selected, only two analog input channel pairs are available for the TLC3544
and four channel pairs for the TLC3548, because half the inputs are used as the negative input (see Figure 7).
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