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Circuit Description
2
2.1
Circuit Description
Schematic Diagram
The schematic diagram for the EVM is in
2.2
Circuit Function
The following sections describe the function of individual circuits. Refer to the relevant data sheet for
device operating characteristics.
2.2.1
Power
Power is supplied to the EVM via banana jack sockets. By default, the EVM is configured to use a power
management solution to supply the ADC and analog and digital power supplies, allowing users to power
the board with a single 5-V power supply. The ADC power management solution is based on TI's
TPS77533 and TPS73218, which supply 3.3 V and 1.8 V, respectively. In addition, the EVM offers the
capability to supply to the ADC independent 3.3-V analog and 1.8-V digital supplies. The circuit board
uses only one ground plane, and the heat slug is tied to ground with multiple vias to provide for thermal
dissipation.
offers a snapshot of the power-supply options.
Table 2. EVM Power-Supply Options
EVM Banana Jack
J1
J2
J4
J5
Single ground plane
ADS528x 3.3-V analog supply (only active when JP8 = 2–3)
ADS528x 1.8-V digital supply (only active when JP9 = 2–3)
DESCRIPTION
Auxiliary circuit 5-V digital supply: PECL driver and USB circuitry
2.2.2
Clock Input
A single-ended square or sinusoidal clock input should be applied to J26. The clock frequency should not
exceed the maximum speed rating found in the data sheet. Several different clocking options exist to allow
flexible evaluation of the ADC.
In the default case, a single-ended clock is converted to a differential clock using a Mini-Circuits TC1-1T
transformer. When using this option, the ADC should be configured in differential clock mode by writing
0x8001 to ADC register address 0x42. By default, after a software reset this option is asserted to coincide
with the EVM default.
A second EVM option allows the ADC to be configured in single-ended mode. This is provided to the ADC
using an On Semiconductor™ MC100EPT21 amplifier, which provides for sine-wave to square-wave
conversion. This configuration can be used for both ADS528X and ADS527X devices. To use this mode,
use the surface-mount jumpers JP3, JP4, and JP5, and configure each one of them to have positions 2–3
shorted.
2.2.3
External References
The EVM offers the ability to force external references to the ADC. By default, the ADC is configured to
use the references generated internal to the ADC. To force the ADC to use external references, users
must short JP2 pads 2–3, which in turn grounds the INT/EXT pin of the ADC. Users can then use J6 pin 1
to force a REFB and pin 3 to force a REFT voltage. GND should be connected to J6 pin 2.
8
SLAU205 – January 2008
TI [ TEXAS INSTRUMENTS ]
