TLC2543-EP Datasheet, PDF (18/25 Pages) Texas Instruments – 12-BIT ANALOG-TO-DIGITAL CONVERTER WITH SERIAL CONTROL AND 11 ANALOG INPUTS

TLC2543-EP
12-BIT ANALOG-TO-DIGITAL CONVERTER
WITH SERIAL CONTROL AND 11 ANALOG INPUTS
SGLS125A – JULY 2002 – REVISED NOVEMBER 2006
www.ti.com
Table 4. Test-Mode-Select Address
INTERNAL SELF-TEST
VOLTAGE SELECTED⁽¹⁾
VALUE SHIFTED INTO DATA INPUT
BINARY
HEX
UNIPOLAR OUTPUT
RESULT (HEX)⁽²⁾
V_{ref +} – V_{ref –}
1011
B
2
V_ref–
V_ref+
1100
C
1101
D
800
000
FFF
(1) V_ref+ is the voltage applied to REF+, and V_ref– is the voltage applied to REF–.
(2) The output results shown are the ideal values and may vary with the reference stability and with
internal offsets.
Table 5. Power-Down-Select Address
INPUT COMMAND
Power down
VALUE SHIFTED INTO DATA INPUT
BINARY
HEX
1110
E
RESULT
I_CC ≤25 µA
Converter and Analog Input
The CMOS threshold detector in the successive-approximation conversion system determines each bit by
examining the charge on a series of binary-weighted capacitors (see Figure 1). In the first phase of the
conversion process, the analog input is sampled by closing the S_C switch and all S_T switches simultaneously.
This action charges all the capacitors to the input voltage.
In the next phase of the conversion process, all S_T and S_C switches are opened and the threshold detector
begins identifying bits by identifying the charge (voltage) on each capacitor relative to the reference (REF–)
voltage. In the switching sequence, 12 capacitors are examined separately until all 12 bits are identified and the
charge-convert sequence is repeated. In the first step of the conversion phase, the threshold detector looks at
the first capacitor (weight = 4096). Node 4096 of this capacitor is switched to the REF+ voltage, and the
equivalent nodes of all the other capacitors on the ladder are switched to REF–. When the voltage at the
summing node is greater than the trip point of the threshold detector (approximately one-half V_CC), a bit 0 is
placed in the output register and the 4096-weight capacitor is switched to REF–. When the voltage at the
summing node is less than the trip point of the threshold detector, a bit 1 is placed in the register and this
4096-weight capacitor remains connected to REF+ through the remainder of the successive-approximation
process. The process is repeated for the 2048-weight capacitor, the 1024-weight capacitor, and so forth down
the line until all bits are determined. With each step of the successive-approximation process, the initial charge
is redistributed among the capacitors. The conversion process relies on charge redistribution to determine the
bits from MSB to LSB.
Reference Voltage Inputs
The two reference inputs used with the device are the voltages applied to the REF+ and REF– terminals. These
voltage values establish the upper and lower limits of the analog input to produce a full-scale and zero-scale
reading, respectively. These voltages and the analog input should not exceed the positive supply or be lower
than ground consistent with the specified absolute maximum ratings. The digital output is at full scale when the
input signal is equal to or higher than REF+ terminal voltage, and at zero when the input signal is equal to or
lower than REF– terminal voltage.
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