CDB5534U

4

DS289DB6

Table 1. Voltage Reference Selection for VREF+

Table 2. Voltage Reference Selection for VREF-

1.2.2

Digital Section

Figure 2 illustrates the schematic of the digital section. It contains the microcontroller, USB interface, EE-

PROM, JTAG header, reset circuitry, and an external interface header. The microcontroller interfaces the

that the SCLK and SDI signals are level shifted to support both +3.3 V and +5 V digital operation.

The microcontroller EEPROM is used to store firmware. An external interface header, J19, is provided to

allow the CDB5534U to be interfaced with an external microcontroller. To use this serial interface, the

0 ohm resistors R9, R10, R23, and R27 should be removed to disconnect the on-board microcontroller

from the serial interface.

1.2.3

Power Supply Section

Figure 3 illustrates the power supply connections to the evaluation board. VA+ supplies the positive ana-

log supply for the CS5534 and the LT1019 reference. Header J14 allows the VA+ supply to be sourced

from either the VA+ binding post (J2), or from the +5 V binding post (J3). VA- supplies the negative analog

supply for the analog section. Header J13 allows the VA- supply to be sourced from either the VA- binding

post (J1), or connected to the board ground. Note that the VA- supply should be connected to ground

when powering the CDB5534U from a single +5 V analog supply. VD+ supplies the digital section of the

ADC and level shifters. Header J15 allows the VD+ supply to be sourced from the VD+ binding post (J5),

Reference

Description

J17

VA+

Selects Positive

Analog Power

Supply

LT1019

Selects on-Board

LT1019 Reference

(5ppm/

VREF+

Selects External

Reference Source

(J12)

Reference

Description

J18

VA-

Selects Negative

Analog Power

Supply

GND

Selects Board

Gnd

VREF-

Selects External

Reference Source

(J12)

O

O VREF+

O

O VREF+

O

O VREF+

VA+

LT1019

REF+

O

O VREF+

O

O VREF+

O

O VREF+

VA+

LT1019

REF+

O

O VREF+

O

O VREF+

O

O VREF+

VA+

LT1019

REF+

O

O VREF-

O

O VREF-

O

O VREF-

VA-

GND

REF-

O

O VREF-

O

O VREF-

O

O VREF-

VA-

GND

REF-

O

O VREF-

O

O VREF-

O

O VREF-

VA-

GND

REF-