Texas Instruments ADS1224EVM, Руководство пользователя

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Switches
2-12
Table 2−8. Common S5−6 Combination Settings
Setting
Number S6
(VRN) S5
(VRP)
Setting VRP and OBREF
Voltage ADS1224 Reference
Voltage
1 EXT EXT Onboard 2.5V 2.5V External (J1 pin 20)
2 EXT 0V Onboard 2.5V,
high common-mode AVDD AVDD − 2.5V
3 EXT VRP External SYSREFP SYSREFP − SYSREFN
4 0V 0V Ratiometric SYSREFP SYSREFP
Setting 1 is most commonly used for the onboard reference.
Setting 2 causes the reference common-mode to be higher; in a very few situa-
tions, this may improve performance, as long as the AVDD supply is quiet.
Setting 2 may also be useful for certain ratiometric connections.
Setting 4 is most often used in ratiometric sensor connections. A sensor excita-
tion voltage can be applied to the SYSREFP pin on J1. Note that the ADS1224
performance is greatly degraded over temperature for reference voltages
above 2.5V.
The voltage selected from S5 is routed to the OBREF pin on J1, and also to
the rightmost position of switches S1−4. This configuration allows any of the
inputs to be connected to the positive reference by moving the switches to the
appropriate setting.
2.3.3 S5: System Clock Select
This switch selects which of the two available clock sources on the
ADS1224EVM will be provided to the ADS1224. The positions of the switch
are described in Table 2−9.
Table 2−9. System Clock Select Switch
Board Marking Switch Position
System Clock Source
EXT Up External (J5 pin 17)
OB Down Onboard 4MHz oscillator