ADS8331_15 Datasheet, PDF (34/57 Pages) Texas Instruments – Low-Power, 16-Bit, 500-kSPS, 4-/8-Channel Unipolar Input Analog-to-Digital Converters

ADS8331, ADS8332
SBAS363D – DECEMBER 2009 – REVISED OCTOBER 2015
www.ti.com
Figure 49 shows a slightly different scenario where CONVST is not shared with the second converter. Converters
#1 and #3 have the same CONVST signal. In this case, converter #2 simply passes previous conversion data
downstream.
Manual Trigger, Read While Sampling
(Use internal CCLK, EOC active low, and TAG mode disabled)
CONVST #1
CONVST #3
CONVST #2
EOC #1
(active low)
CS #1
SCLK #1
SCLK #2
SCLK #3
SDO #1
CDI #2
CS #2
CS #3
Conversion N
t_CONV = 18 CCLK
High-Z
1. . . . . . . . . . . . . .16
Conversion N
from Device #1
t_SAMPLE1 = 3 CCLK min
1. . . . . . . . . . . . . .16
1. . . . . . . . . . . . . .16
t_SU2
High-Z
t_SU2
SDO #2
CDI #3
High-Z
Conversion (N - 1)
from Device #2⁽¹⁾
Conversion N
from Device #1
High-Z
SDO #3
High-Z
Conversion N
from Device #3
Conversion (N - 1)
from Device #2⁽¹⁾
Conversion N
from Device #1
High-Z
SDI #1
SDI #2
SDI #3
Don't Care
Configure
Read Data
Read Data
Don't Care
(1) Data from device #2 is from previous converison.
Figure 49. Simplified Daisy-Chain Mode Timing with Separate CONVST and Continuous CS
The number of SCLKs required for a serial read cycle depends on the combination of different read modes, TAG
mode, daisy-chain mode, and the manner in which a channel is selected (for example, Auto Channel Select
mode). The required number of SCLKs for different readout modes are listed in Table 7.
Table 7. Required SCLKs kor Different Readout Mode Combinations
DAISY-CHAIN MODE
CFR_D5
1
1
0
0
TAG MODE
CFR_D1
0
1
0
1
NUMBER OF SCLK CYCLES
PER SPI READ
16
≥ 19
16
24
TRAILING BITS
None
TAG bits plus up to 5 zeros
None
TAG bits plus 5 zeros
SCLK skew between converters in a daisy-chain configuration can affect the maximum frequency of SCLK. The
skew can also be affected by supply voltage and loading. It may be necessary to slow down the SCLK when the
devices are configured in daisy-chain mode.
8.5.5 Reset Function
The ADS833x can be reset with three different methods: internal POR, software reset, and external reset using
the RESET pin.
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