Texas Instruments ADS1241, Руководство пользователя, Страница: 4 / 10

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4.1 ADC Power
4.2 Stand-Alone Operation
4.3 Reference Voltage
Power Supplies
Power for the ADS1241 analog supply voltage (AVDD) comes from +5VA, which is supplied
through J3.3. The shunt from J4 pins 1 to 2 applies this supply to the ADS1241 device.
The ADS1241 digital supply voltage (DVDD) is selected using J4. When a shunt is applied from
J4 pins 5 to 6, +5VD is selected, and this power comes from J3.10. If a shunt is placed from J4
pins 7 to 8 (the default factory setting), +3.3VD is selected, which is provided from J3.9. J4 pins
9 and 10 provide a way to connect the analog and digital grounds; these pins are connected by
default when the EVM is shipped from the factory.
CAUTION
Verify that all power supplies are within the safe operating limits shown on
the ADS1241 data sheet before applying power to the EVM. Note that a
shunt should only be connected between J4 pins 7 and 8 OR pins 5 and 6,
but never both; doing so would short the +3.3V supply to the +5V digital
supply.
When used as a stand-alone EVM, the analog power can be applied to J4.1, referenced to
J4.10. DVDD can be applied to J4.3, referenced to J4.10. Note that this EVM uses only a single
ground plane.
The ADS1241 requires an external voltage reference. Two switches, S6 and S7, select the
source of the reference for the ADS1241. An external reference may be supplied through J1 pin
20 on the ADS1241MEVM. A 2.5V reference is provided on the EVM for convenience, or the
supply voltage may also be used as the device reference voltage. These different reference
sources can be selected using S6 and S7, as shown in
Table 4 . Note that the ADS1241
reference is differential, so both VREF+ and VREF- pins may take on several voltages. Refer to
the ADS1241 data sheet.
CAUTION
Verify that the external reference voltage is within the safe operating limits
shown on the ADS1241 data sheet before applying power to the EVM.
Table 4. Reference Selection Options - S6 and S7
S6 Position S7 Position VREF+ VREF- Comment
Left Left External (J1.20) External (J1.18)
Middle Left 2.5V External (J1.18)
Right Left AVDD External (J1.18)
Left Middle External (J1.20) Ground
Middle Middle 2.5V Ground
Right Middle AVDD Ground
Left Right External (J1.20) 2.5V
This results in a 0V
Middle Right 2.5V 2.5V reference - not a very
useful setting.
Right Right AVDD 2.5V
ADS1241MEVM 4 SBAU106 – October 2004