Power Supplies
9
SBAU291 – November 2017
Copyright © 2017, Texas Instruments Incorporated
ADS8168EVM-PDK
4
Power Supplies
The ADS8168 ADC analog supply (AV
DD
) is provided by a low-noise linear regulator (TPS7A4700). The
regulator uses a 5.5-V supply out of a switching regulator from the PHI controller to generate a quiet and
stable 5.3-V supply output. The 3.3-V supply to the digital supply of the ADS8168 is provided directly by
an LDO from the PHI controller. The power supply for each active component on the EVM is bypassed
with a ceramic capacitor placed close to that component. Additionally, the EVM layout uses thick traces or
large copper filled areas, where possible, between bypass capacitors and their loads to minimize
inductance along the load current path.
CAUTION
In default configuration, the ADS8168EVM is designed to be used in
conjunction with the PHI controller, and in this configuration, all required
voltages are supplied. Do not apply external power sources to the EVM while in
its default configuration.
CAUTION
If external power supply sources are connected, ensure that modifications are
performed according to
Table 3. Required Modifications for External Power Connection
External Supply
Default Voltage
Connection Location
Required Modification
AV
DD
5.3 V
P1.1
Remove R18, labeled "AVdd"
GND
0 V
P1.2, P1.5
None
AV
SS
0 V
P1.3
Remove R10, labeled "AVss"
5.5 V
5.5 V
P1.4
Remove R5, labeled "5.5V"
DVdd
3.3 V
P1.6
Remove R2, labeled "DVdd"
•
5.5 V is only used for developing AV
DD
, via U2. If external AV
DD
is applied, the 5.5-V voltage node is
not necessary. Apply a minimum of AV
DD
+ 0.2 V, and Do not exceed the rated maximum for U2,
TPS7A4700.
•
AV
DD
is the positive rail for the input driver amplifiers and the ADC driver amplifiers and for the
ADS8168. Use caution not to exceed the maximum rated voltage for these components, taking into
account the value of AV
SS
.
•
If an external reference is used for the ADS8168, AV
DD
must be 0.2 V higher than the external
reference for proper operation of the internal reference buffer of the ADS8168.
•
AV
SS
is used as the negative rail for the input amplifiers and the ADC driver amplifiers. AV
SS
can be set
to a small negative voltage value in order to allow the amplifiers to drive a signal to a true zero-volt
value.
•
AV
SS
should be limited to AV
DD
– 5.5 V (nominally, 200 mV) to protect the OPA350 circuits onboard.
