ADS8634 Datasheet, PDF (29/75 Pages) Texas Instruments – 12-Bit, 1MSPS, 4-/8-Channel, Bipolar-Input, SAR Analog-to-Digital Converter

ADS8634
ADS8638
www.ti.com
SBAS541A – MAY 2011 – REVISED AUGUST 2011
Figure 80 shows a functional block diagram for a single-channel alarm. For each high and low alarm there are
two flags: Active Alarm Flag and Tripped Alarm Flag; refer to the Alarm Flags for the ADS8638 (Read-Only) and
Alarm Flags for the ADS8634 (Read-Only) sections for more details. The active alarm flag is triggered when an
alarm condition is encountered for a particular channel; the active alarm flag resets when the alarm shuts off. A
tripped alarm flag sets an alarm condition in the same manner as it does for an active alarm flag; however, it
remains latched and resets only when the appropriate alarm flag register is read.
Alarm Threshold
Channel n
+/-
Hysteresis Channel n
ADC Output
Channel n
ADC
+
16^th
SCLK
SQ
RQ
AL_PD
Programmed
as Alarm
Output
Active Alarm Flag
Channel n
Tripped Alarm Flag
Channel n
Alarm Flag Read
SDO
Figure 80. Alarm Functionality
Power-Down Functionality
The ADS8634/8 feature a power-down/up control through the programmable AL_PD pin or the channel
sequencing control registers; see the Channel Sequencing Control Registers for the ADS8638 and Channel
Sequencing Control Registers for the ADS8634 sections for more details. This feature is extremely useful for
saving power while running the ADS8634/8 at a slower speed, or for acquiring data at full-speed in bursts and
then waiting in a power-down state for the next acquisition start event. Figure 81 through Figure 84 describe
entry to and exit from the power-down state.
The AL_PD pin can be programmed as a power-down control pin. The AL_PD pin, when programmed as PD, is
shown in Figure 81. A low on AL_PD powers down the device immediately; this action is asynchronous
operation. Data on DOUT are not valid when the device is in a power-down state.
AL_PD
Programmed as PD
Power-Down State
(Internal)
Active
Power-Down
DOUT
Valid data terminates on power down.
Figure 81. Power-Down Using the AL_PD Pin
Copyright © 2011, Texas Instruments Incorporated
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