Datasheet

OVERVIEW
DS
Modulator1
Digital
Filter1
VREFP
V
IN1
VREFN
V
REF
S
TEST[1:0]
FORMAT[2:0]
CLK
SYNC
PWDN
(1)
[4:1]/[8:1]
CLKDIV
MODE
DRDY/FSYNC
SCLK
DOUT[4:1]/[8:1]
(1)
DIN
SPI
and
Frame-Sync
Interface
Control
Logic
AINP1
AINN1
VCOM
S
DS
Modulator2
Digital
Filter2
V
IN2
S
AINP2
AINN2
DS
Modulator4/8
(1)
Digital
Filter4/8
(1)
V
IN4/8
S
AINP4/8
(1)
AINN4/8
(1)
DVDDAVDD
AGND DGND
IOVDD
R
R
NOTE:(1)TheADS1174hasfourchannels;theADS1178haseightchannels.
ADS1174
ADS1178
www.ti.com ........................................................................................................................................ SBAS373B – OCTOBER 2007 – REVISED SEPTEMBER 2008
To allow tradeoffs between speed and power, two
The ADS1174 (quad) and ADS1178 (octal) are 16-bit,
modes of operation are supported: High-Speed and
delta-sigma ADCs. They offer the combination of
Low-Power. Table 1 summarizes the performance of
excellent linearity, low noise, and low power
each mode.
consumption. Figure 1 shows the block diagram. Note
that both devices are the same, except the ADS1174 In High-Speed mode, the data rate is 52kSPS, and in
has four ADCs, and the ADS1178 has eight ADCs. Low-Power mode, the power dissipation is only
The pinout and package of the ADS1178 are 7mW/channel at 10.5kSPS.
compatible with the ADS1174 (and the 24-bit
The ADS1174/78 is configured by simply setting the
ADS1274 and ADS1278 ), permitting drop-in
appropriate I/O pins — there are no registers to
expandability or upgrades. The converters are
program. Data are retrieved over a serial interface
comprised of either four (ADS1174) or eight
that supports both SPI and Frame-Sync formats. The
(ADS1178) advanced, 6th-order, chopper-stabilized,
ADS1174/78 has a daisy-chainable output and the
delta-sigma modulators followed by low-ripple, linear
ability to synchronize externally, so it can be used
phase FIR filters. The modulators measure the
conveniently in systems requiring more than eight
differential input signal, V
IN
= (AINP – AINN), against
channels.
the differential reference, V
REF
= (VREFP – VREFN).
The digital filters receive the modulator signal and
provide a low-noise digital output.
Figure 1. ADS1174/ADS1178 Block Diagram
Table 1. Operating Mode Performance Summary
POWER DISSIPATION
DATA RATE PASSBAND SNR NOISE PER CHANNEL
(1)
MODE (SPS) (Hz) (dB) (LSB
PP
) (mW)
High-Speed 52,734 23,889 97 1 31
Low-Power 10,547 4,778 97 1 7
(1) Measured with all channels operating.
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