Texas Instruments ADS1271EVM User Manual page 5

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When power is supplied to J3, J6 allows for either 3.3V or 1.8V to be applied to the digital sections of the
ADS1271. J6 also provides for a method of measuring AVDD and DVDD supply currents if the shunts on
J6.1-2, J6.3-4, J6.5-6, and J6.7-8 are removed and a current meter is connected between the appropriate
pins. See the schematic and printed circuit board silkscreen for details.
4.1 ADC Power
Power for the ADS1271 analog supply voltage (AVDD) comes from +5V
The shunt from J6 pins 1 to 2 applies this supply to the U7 ADS1271 device, while the shunt from J6 pins
5 to 6 applies this supply to the U8 ADS1271.
The ADS1271 digital supply voltage (DVDD) is selected using J6. When a shunt is applied from J6 pins 9
to 10, +1.8VD is selected, and this power comes from J3.7. If a shunt is placed from J6 pins 11 to 12 (the
default factory setting), +3.3V
means of connecting analog and digital grounds to the EVM; these grounds come from J3.6 and J3.5,
respectively. These grounds are always connected together at the EVM.
Verify that all power supplies are within the safe operating limits shown on
the ADS1271 data sheet before applying power to the EVM. Note that a
shunt should only be connected between J6 pins 9 and 10 OR pins 11 and
12, but never both; doing so would short the +3.3V supply to the +1.8V
digital supply.
4.2 Stand-Alone Operation
When used as a stand-alone EVM, the analog power can be applied to J6.2 and J6.6, referenced to
J6.13. DVDD can be applied to J6.4 and J6.8, referenced to J6.15. Note that this EVM uses only a single
ground plane.
4.3 Reference Voltage
The ADS1271 requires an external voltage reference. Two switches, S3 and S5, select the source of the
reference for the two ADS1271s on the EVM. An external reference may be supplied through J1 pin 20 on
the ADS1271EVM, or through J4 and J5, the auxiliary analog input connectors. A 2.5V reference is
provided on the EVM for convenience. These different reference sources can be selected using S3 and
S5, as shown in Table
Verify that the external reference voltage is within the safe operating limits
shown on the ADS1271 data sheet before applying power to the EVM.
S3/S5 Position
Left
Middle
Right
SBAU107 – November 2004
is selected, which is provided from J3.9. J6 pins 13 and 15 provide a
D
6.
Table 6. Reference Selection Options - S3 and S5
, which is supplied through J3.3.
A
CAUTION
CAUTION
Reference Inputs
Onboard 2.5V reference
External Reference from J1.20 (REFP) referenced to J1.18
(REFN)
S3: AUXREF1 from J4.3 referenced to J4.4
S5: AUXREF2 from J5.3 referenced to J5.4
ADS1271EVM & ADS1271EVM-PDK
Power Supplies
5