ADS1178IPAPR datasheet(23/39 Pages) TI1

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POWER SUPPLIES

DRDY

(SPIProtocol)

DOUT

(Frame-SyncProtocol)

InternalReset

CLK

3Vnom

(1)

AVDD

1Vnom

(1)

IOVDD

1Vnom

(1)

DVDD

ValidData

CLK

129(max)

DATA

ADS1174

ADS1178

www.ti.com ........................................................................................................................................ SBAS373B – OCTOBER 2007 – REVISED SEPTEMBER 2008

be sequenced at the same time if the supplies are

tied together. Each supply has an internal reset circuit

The ADS1174/78 has three power supplies: AVDD,

whose outputs are summed together to generate a

DVDD, and IOVDD. AVDD is the analog supply that

global power-on reset. After the supplies have

powers the modulator, DVDD is the digital supply that

exceeded the reset thresholds, 218 fCLK cycles are

powers the digital core, and IOVDD is the digital I/O

counted before the converter initiates the conversion

power supply. The IOVDD and DVDD power supplies

process. Following the CLK cycles, the data for 129

can be tied together if desired (+1.8V). To achieve

conversions are suppressed by the ADS1174/78 to

rated performance, it is critical that the power

allow output of fully-settled data. In SPI protocol,

supplies

are

bypassed

with

0.1

µF and 10µF

DRDY is held high during this interval. In frame-sync

capacitors placed as close as possible to the supply

protocol, DOUT is forced to zero. The power supplies

pins. A single 10

µF ceramic capacitor may be

should be applied before any analog or digital pin is

substituted in place of the two capacitors.

driven. For consistent performance, assert SYNC

after device power-on when data first appear.

Figure 24 shows the start-up sequence of the

ADS1174/78. At power-on, bring up the DVDD supply

first, followed by IOVDD and then AVDD. Check the

power-supply sequence for proper order, including

the ramp rate of each supply. DVDD and IOVDD may

(1) The power-supply reset thresholds are approximate.

Figure 24. Start-Up Sequence

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ADS1178IPAPR Datasheet(PDF) 23 Page - Texas Instruments

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