DDC232_15 Datasheet, PDF (26/34 Pages) Texas Instruments – 32-Channel, Current-Input Analog-to-Digital Converter

DDC232
SBAS331D – AUGUST 2004 – REVISED APRIL 2010
POWER-UP SEQUENCING
Prior to power-up, all digital and analog inputs must
be low. At the time of power-up, all of these signals
should remain low until the power supplies have
stabilized, as shown in Figure 24. At this time, begin
supplying the master clock signal to the CLK pin.
Wait for time t_POR, then give a RESET pulse. After
releasing RESET, the configuration register must be
programmed. Table 16 shows the timing for the
power-up sequence.
Power Supplies
RESET
t_POR
t_RST
CONV
Figure 24. DDC232 Timing at Power-Up
Table 16. Timing Characteristics for DDC232
Power-Up Sequence
SYMBOL
t_POR
t_RST
DESCRIPTION
Wait After Power-Up
Until Reset
Reset Low Width
MIN TYP MAX UNITS
250
ms
1
ms
BLANKSPACE
BLANKSPACE
BLANKSPACE
BLANKSPACE
www.ti.com
LAYOUT
POWER SUPPLIES AND GROUNDING
Both AVDD and DVDD should be as quiet as
possible. It is particularly important to eliminate noise
from AVDD that is nonsynchronous with the DDC232
operation. Figure 25 illustrates how to supply power
to the DDC232. Each supply of the DDC232 should
be bypassed with 10mF solid tantalum capacitors. It is
recommended that both the analog and digital
grounds (AGND and DGND) be connected to a single
ground plane on the printed circuit board (PCB).
VA
0.1mF
AVDD
AGND
10mF
VD
DDC232
0.1mF
DVDD
DGND
10mF
Figure 25. Power-Supply Connections
Shielding Analog Signal Paths
As with any precision circuit, careful PCB layout will
ensure the best performance. It is essential to make
short, direct interconnections and avoid stray wiring
capacitance—particularly at the analog input pins and
QGND. These analog input pins are high-impedance
and extremely sensitive to extraneous noise. The
QGND pin should be treated as a sensitive analog
signal and connected directly to the supply ground
with proper shielding. Leakage currents between the
PCB traces can exceed the input bias current of the
DDC232 if shielding is not implemented. Digital
signals should be kept as far as possible from the
analog input signals on the PCB.
26
Submit Documentation Feedback
Product Folder Link(s): DDC232
Copyright © 2004–2010, Texas Instruments Incorporated