and any data written to the SFR has been lost. Thus, the
ADS7832 will again be in the Transparent Mode. Writing a
LOW to D5 in the SFR resets the Power Fail flag. The Cal
Error flag in the SFR is set when an overflow occurs during
calibration, which may happen in very noisy systems. It is
reset by starting a calibration, and remains low after a
calibration without an overflow is completed.
CS
t1
t2
t3
t6
WR
HBE
t5
Table III shows how instructions can be transferred to the
Special Function Register by driving HBE HIGH (with SFR
HIGH) and initiating a write cycle (driving WR and CS
LOW with RD HIGH.) Note that writing to the SFR also
initiates a new conversion.
SFR
VIH
VIL
Valid Data
t16
D0 - D7
t17
FIGURE 5. Writing to the SFR.
POWER DOWN MODE
Writing a HIGH to D3 in the SFR puts the ADS7832 in the
Power Down Mode. Power consumption is reduced to 50µW
and D3 remains HIGH. The internal clock and analog
circuitry are turned off, although the output registers and
SFR can still be accessed normally. To exit Power Down
Mode, either write a LOW to D3 in the SFR, or initiate a
calibration by sending a LOW to the CAL pin or writing
a HIGH to D1. Note that if the power supply falls below 3V
and then recovers, a calibration is automatically initiated,
and the SFR will be reset. D3 will be HIGH, and the
ADS7832 will be in the Power Down Mode.
CS
RD
HBE
t8
t11
t10
t12
t11
t12
SFR
VIH
t13
t14
SFR Data
D0 - D7
During Power Down Mode, a pulse on CS and WR will
initiate a single conversion, then the ADS7832 will revert to
power down. Also, writing to D1 and D3 in the SFR will
initiate a calibration, do a single conversion and revert to the
Power Down Mode, in 4,625 clock cycles. Accurate conver-
sion results will be available in the output registers.
FIGURE 6. Reading the FSR.
In the Sample/Hold Control Mode, pin 26 must be held
LOW a minimum of 2.5µs between conversions to allow
accurate acquisition of input signals. Also, offset error will
increase in this mode, since auto-zeroing of the comparator
is not synchronized to the sampling. Minimum offset is
achieved by synchronizing the sampling signal to CLK,
whether internal or external. Ideally, the sampling signal
rising edge should be delayed 20ns from the falling edge of
CLK. This will keep offset error to about 1LSB.
The activation delay from power down to normal operation
is included in the sampling time. No extra time is required,
either when coming out of the Power Down Mode or when
making a single conversion in the Power Down Mode.
SAMPLE/HOLD CONTROL MODE
With D2 in the SFR HIGH, a rising edge input on pin 26 will
switch the ADS7832 from sample-mode to hold-mode with
a 5ns aperture delay. This also initiates a conversion, which
will start within 1.5 CLK cycles.
In the Sample/Hold Control Mode, a LOW pulse on WR
(with CS LOW) will not initiate a conversion, but the rising
edge will latch the multiplexer channel according to the
inputs on A0 and A1. When changing channels, this must be
done at least 2.5µs before pin 26 goes HIGH (to start a
conversion.)
This mode allows full control over the sample-to-hold tim-
ing, which is especially useful where external events trigger
sampling timing.
OPERATION
CS/WR
SFR/HBE
D0
D1
D2
D3
D5
D4/D6/D7
Enables Transparent Mode for Data Latches
Enables Latched Output Mode for Data Latches
Initiates Calibration Cycle
LOW
LOW
LOW
LOW
LOW
LOW
HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
LOW
HIGH(1)
X
X
X
X
X
X
LOW
LOW
LOW
LOW
LOW
LOW
X
X
X
X
X
X
HIGH
X
X
X
X
Activates Sample/Hold Control Mode
Activates Power Down Mode(2)
HIGH(1)
X
HIGH(1)
X
X
X
X
X
X
Resets Power Fail Flag
X
LOW
NOTES: (1) Writing a LOW here reactivates the standard mode of operation. (2) In Power Down Mode, a pulse on CS and WR will initiate a single conversion,
then the ADS7832 will revert to power down. (3) X means it can be either HIGH or LOW without affecting this action. Writing HIGH to D4 or D6, or writing with
SFR HIGH and HBE LOW, may result in unpredictable behavior. These modes are reserved for factory use at this time.
TABLE III. Writing to the Special Function Register.
®
11
ADS7832
BB [ BURR-BROWN CORPORATION ]
