DDC232CK datasheet(26/35 Pages) TI2

26 / 35 page

PowerSupplies

RESET

POR

RST

CONV

AVDD

DVDD

AGND

DGND

DDC232

10 F

0.1 F

10 F

DDC232

SBAS331D – AUGUST 2004 – REVISED APRIL 2010

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POWER-UP SEQUENCING

LAYOUT

Prior to power-up, all digital and analog inputs must

POWER SUPPLIES AND GROUNDING

be low. At the time of power-up, all of these signals

should remain low until the power supplies have

Both AVDD and DVDD should be as quiet as

stabilized, as shown in Figure 24. At this time, begin

possible. It is particularly important to eliminate noise

supplying the master clock signal to the CLK pin.

from AVDD that is nonsynchronous with the DDC232

Wait for time tPOR, then give a RESET pulse. After

operation. Figure 25 illustrates how to supply power

releasing RESET, the configuration register must be

to the DDC232. Each supply of the DDC232 should

programmed. Table 16 shows the timing for the

be bypassed with 10mF solid tantalum capacitors. It is

power-up sequence.

recommended that both the analog and digital

grounds (AGND and DGND) be connected to a single

ground plane on the printed circuit board (PCB).

Figure 24. DDC232 Timing at Power-Up

Figure 25. Power-Supply Connections

Table 16. Timing Characteristics for DDC232

Power-Up Sequence

Shielding Analog Signal Paths

SYMBOL

DESCRIPTION

MIN

TYP

MAX

UNITS

As with any precision circuit, careful PCB layout will

Wait After Power-Up

ensure the best performance. It is essential to make

tPOR

250

Until Reset

short, direct interconnections and avoid stray wiring

tRST

Reset Low Width

capacitance—particularly at the analog input pins and

QGND. These analog input pins are high-impedance

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and extremely sensitive to extraneous noise. The

QGND pin should be treated as a sensitive analog

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signal and connected directly to the supply ground

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with proper shielding. Leakage currents between the

PCB traces can exceed the input bias current of the

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DDC232 if shielding is not implemented. Digital

signals should be kept as far as possible from the

analog input signals on the PCB.

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