Datasheet

ADS7924
www.ti.com SBAS482A –JANUARY 2010–REVISED MAY 2010
Sleep Time
ADC CONVERSION TIMING
The sleep time is allowed to elapse after conversions
The ADS7924 provides a flexible timing arrangement
in the Auto-Single with Sleep, Auto-Scan with Sleep,
to support a wide variety of measurement needs.
and Auto-Burst Scan with Sleep modes. The nominal
Three user-controlled timings include power up (t
PU
),
time programmed by the SLPTIME registers can be
acquisition (t
ACQ
), and sleep (t
SLEEP
) plus a fixed
increased by a factor of eight using the SLPMULT8
conversion time (t
CONV
).
bit or decreased by a factor of four using the
SLPDIV4 bit.
Power-Up Time
The power-up time is allowed to elapse whenever the
INTERRUPT OUTPUT (INT)
device has been shutdown in idle mode. Power-up
time can allow external circuits, such as an op amp, The ADS7924 offers a dedicated output pin (INT) for
between the MUXOUT and ADCIN pins to turn on. signaling an interrupt condition. The INT pin can be
The nominal time programmed by the PUTIME[4:0] configured to activate when the ADC is busy with a
register bits is given by Equation 1: conversion, when data are ready for retrieval, or
when an alarm condition occurs; see the Interrupt
t
PU
= PWRUPTIME[4:0] × 2ms (1)
Configuration register in the Register Map section.
For example, if PWRUPTIME is set to 25 ('011001')
To clear an interrupt from an alarm condition, read
then 50ms is allowed to elapse before beginning the
the INTCONFIG register (12h). To clear an interrupt
acquisition time. If a power-up time is not required,
from data ready, read the data registers. The interrupt
set the bits to '0' to effectively bypass.
clears when the lower four bits are retrieved.
Acquisition Time
The INT pin can be configured to generate a static
output (useful for a host controller monitoring for a
The acquisition time is allowed to elapse before
level) or a pulse output (useful for a host controller
beginning a conversion. During this time, the ADC
monitoring for a edge transition). When a pulse
acquires the signal. The minimum acquisition time is
output is selected, the nominal pulse width is 250ns.
6µs. The nominal time programmed by the
The Interrupt Control Register should be read to clear
ACQTIME[4:0] register bits is given by Equation 2:
the interrupt.
t
ACQ
= (ACQTIME[4:0] × 2ms) + 6ms (2)
For example, if ACQTIME is set to 30 ('011110') then
PWRCON
66ms is allowed to acquire the input signal. If an
The PWRCON pin allows the user to synchronize the
acquisition time greater than 6ms is not required, set
shutdown/wakeup of an external op amp with the
the bits to '0'.
ADC conversion cycle. This feature provides further
power reduction and can be useful in applications
Conversion Time
where the time difference between consecutive signal
The conversion time is always 4ms and cannot be
captures is large. The PWRCON pin can drive up to
programmed by the user.
3mA of current and its output voltage is the same as
AVDD. This pin is controlled by the PWRCONFIG
register.
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