Circuit Function
3-5
Circuit Description
for a 5-volt or 2.7-volt V
CC
such that ADC evaluation can be done at either VDD
through switch SW1. SW1 adjusts the TL1431 voltage reference to accommo-
date the change in V
CC
; SW1 also changes the SN74HC244 V
CC
to 2.7 volts.
The micro inverter can be used to accommodate inversion for software inter-
rupt processing.
3.2.6
Voltage Reference Generation
Two jumpers control the reference voltage for the ADC. JP1 supplies a 5-volt
reference in position 3 with a 5 volt supply and 2.7 volt reference with the 2.7
volt supply selected. (pins 2 and 3 shorted together). A nominal 4.086-volt
reference is obtained with the jumper in position 1 (pins 1 and 2 shorted
together or a 2.5 volt reference with the 2.7 volt supply). This absolute
reference is generated by the TL1431 through the resistor divider of R2 and
R3. R2 is shorted when the ADC is operated at 2.7 volt Vcc giving the voltage
reference of 2.5 volts. JP2 should be connected to ground in position 1 toward
the TP11 designator (shorting pins 2 and 3 together). The jumper can be
changed to position 2 toward the TP27 designator (pins 1 and 2 shorted
together), which removes the ground connection such that a positive voltage
can be applied to TP27 as the REF– input. Care must be exercised when using
this reference method to provide a clean, noise free voltage at the REF–
terminal of the ADC. The voltage differential between REF+ and REF – should
always be equal to or greater than 2.5 volts for proper operation within the
TLV1544 specified limits.
Ratiometric measurements are the measurements made on signals that vary
with the supply voltage. If an input signal voltage is used that varies proportion-
ately with the supply voltage, such as the potentiometer input to A0, the signal
is a ratio of the absolute value of the supply. Therefore, connecting the refer-
ence to the supply provides a nominal conversion result independent of supply
voltage variations.
3.2.7
Test Connector
Test connector J7 provides a convenient point for measuring device
signal.The device test points as listed in Table 3–1.
Table 3–1. Test Connector J7
J7 Pin
TLV1544 pin
Function
1
GND
GND
2
4
EOC
3
3
I/O CLK
4
2
DATA IN
5
1
DATA OUT
6
16
CS
7
13
FS
8
GND
GND
Summary of Contents for TLV1544EVM
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Page 8: ...vi...
Page 16: ...1 6 Overview...
Page 19: ...PCB Layout 2 3 Physical Description Figure 2 2 PCB Layout...
Page 20: ...PCB Layout 2 4 Physical Description Figure 2 3 PCB Layout...
Page 21: ...PCB Layout 2 5 Physical Description Figure 2 4 PCB Layout...
Page 22: ...PCB Layout 2 6 Physical Description Figure 2 5 PCB Layout...
