Datasheet

DRDY
STARTPin
DataReady,IndextoNextChannel
IdleIdleMode Converting
DRDY
STARTPin
PulseConvert
Command
Converting ConvertingIdle
DataReady,IndextoNextChannel
or
DRDY
STARTPin
t
SDSU
t
DRHD
SYMBOL DESCRIPTION MIN UNIT
t
SDSU
8
t
CLK
8
t
CLK
t
DRHD
STARTto SetupTime
DRDY
toHaltFurtherConversions
DRDY toSTARTHoldTime
toCompleteCurrentConversion
ADS1158
www.ti.com SBAS429D –JUNE 2008– REVISED MARCH 2011
Offset Reading (OFFSET)
The differential output of the multiplexer is shorted
together and set to a common-mode voltage of
(AVDD – AVSS)/2. Ideally, the code from this register
function is 0h, but varies because of the noise of the
ADC and offsets stemming from the ADC and
external signal conditioning. This register can be used
to calibrate or track the offset of the ADS1158 and
Figure 40. Conversion Control, Auto-Scan Mode
external signal conditioning. The chop feature of the
ADC can automatically remove offset and offset drift
Pulse Convert Command
from the external signal conditioning; see the External
Chopping section.
Figure 41 also shows the start of conversions with the
rising edge of the START pin. If the START pin is
CONVERSION CONTROL
taken high, and then low before completion of the
conversion cycle (8 τ
CLK
before DRDY asserts low),
The conversions of the ADS1158 are controlled by
only the current channel is converted and the device
the START pin. Conversions begin when the START
enters the standby or sleep modes and waits for a
pin is taken high and conversions are stopped when
new start condition. Figure 42 shows the START pin
the START pin is taken low. For continuous
to DRDY timing. The same function of conversion
conversions, tie the START pin high. The START pin
control is possible using the Pulse Convert command
can also be tied low and the conversions controlled
(with the START pin low). In this operation, the data
by the PULSE convert command. The PULSE
from one channel are converted with each Pulse
convert command converts one channel (only) for
Convert command. The Pulse convert command
each command sent. In this way, channel
takes effect when the command byte is completely
conversions can be stepped without the need to
shifted in (eighth falling edge of SCLK). After
toggle the START pin.
conversion, if more than one channel is enabled
(Auto-Scan mode), the converter indexes to the next
START Pin
selected channel after completing the conversion.
As shown in Figure 40, when the START pin is taken
high, conversions start beginning with the current
channel. The device continues to convert all of the
programmed channels, in a continuous loop, until the
START pin is taken low. When this occurs, the
conversion in process completes, and the device
enters the standby or sleep mode and waits for a new
start condition. When DRDY asserts low, the
conversion data are ready. Figure 42 shows the
START pin to DRDY timing. The order in which
channel data are converted is described in Table 9.
When the last selected channel in the program list
has been converted, the device continues
Figure 41. Pulse Conversion, Auto-Scan Mode
conversions starting with the highest priority channel.
If there is only one channel selected in the Auto-Scan
mode, the converter remains fixed on one channel. A
write operation to any of the multiplexer channel
select registers sets the channel pointer to the
highest priority channel (see Table 10). In
Fixed-Channel mode, the channel pointer remains
fixed.
Figure 42. START Pin and DRDY Timing
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