ADS7950_15 Datasheet, PDF (27/70 Pages) Texas Instruments – Single-Ended, MicroPower, Serial Interface ADCs

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8.2 Functional Block Diagram
ADS7950, ADS7951, ADS7952, ADS7953, ADS7954, ADS7955
ADS7956, ADS7957, ADS7958, ADS7959, ADS7960, ADS7961
SLAS605B – JUNE 2008 – REVISED JULY 2015
MXO AINP
REF +VA AGND
Ch0
Ch1
ADC
SDO
Ch2
Compare
Alarm
Threshold
Ch n*
Control Logic
&
Sequencing
SDI
SCLK
CS
GPIO BDGND VBD
NOTE: n* is number of channels (16,12,8, or 4) depending on the device from the ADS79xx product family.
NOTE: 4 number of GPIO are available in TSSOP package devices only, QFN package devices offer only one GPIO.
8.3 Feature Description
8.3.1 Reference
The ADS79xx can operate with an external 2.5-V ± 10-mV reference. A clean, low noise, well-decoupled
reference voltage on the REF pin is required to ensure good performance of the converter. A low noise band-gap
reference like the REF5025 can be used to drive this pin. A 10-μF ceramic decoupling capacitor is required
between the REF and GND pins of the converter. The capacitor should be placed as close as possible to the
pins of the device.
8.3.2 Power Saving
The ADS79xx devices offer a power-down feature to save power when not in use. There are two ways to power
down the device. It can be powered down by writing DI05 = 1 in the Mode Control register (refer to Table 1,
Table 2 and Table 5); in this case the device powers down on the 16th falling edge of SCLK in the next data
frame. Another way to powerdown the device is through GPIO. GPIO3 can act as a PD input (refer to Table 11,
for assigning this functionality to GPIO3). This is an asynchronous and active low input. The device powers down
instantaneously after GPIO3 (PD) = 0. The device will powerup again on the CS falling edge while DI05 = 0 in
the Mode Control register and GPIO3 (PD) = 1.
8.4 Device Functional Modes
8.4.1 Channel Sequencing Modes
There are three modes for channel sequencing, namely Manual mode, Auto-1 mode, Auto-2 mode. Mode
selection is done by writing into the control register (refer to Table 1, Table 2, and Table 5). A new multiplexer
channel is selected on the second falling edge of SCLK (as shown in Figure 1) in all three modes.
Manual mode: When configured to operate in Manual mode, the next channel to be selected is programmed in
each frame and the device selects the programmed channel in the next frame. On powerup or after reset the
default channel is 'Channel-0' and the device is in Manual mode.
Auto-1 mode: In this mode the device scans pre-programmed channels in ascending order. A new multiplexer
channel is selected every frame on the second falling edge of SCLK. There is a separate ‘program register’ for
pre-programming the channel sequence. Table 3 and Table 4 show Auto-1 ‘program register’ settings.
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Product Folder Links: ADS7950 ADS7951 ADS7952 ADS7953 ADS7954 ADS7955 ADS7956 ADS7957 ADS7958
ADS7959 ADS7960 ADS7961