LTC2497 Linear Technology, LTC2497 Datasheet - Page 11

• Manufacturer Part Number: LTC2497
• Description: 16-Bit 8-/16-Channel ADC
• Manufacturer: Linear Technology

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APPLICATIONS INFORMATION
CONVERTER OPERATION
Converter Operation Cycle
The LTC2497 is a multichannel, low power, delta-sigma
analog-to-digital converter with a 2-wire, I
Its operation is made up of four states (see Figure 1).
The converter operating cycle begins with the conver-
sion, followed by the sleep state and ends with the data
input/output cycle .
Initially, at power-up, the LTC2497 performs a conver-
sion. Once the conversion is complete, the device enters
the sleep state. In the sleep state, power consumption is
reduced by two orders of magnitude. The part remains in
the sleep state as long it is not addressed for a read/write
operation. The conversion result is held indefi nitely in a
static shift register while the part is in the sleep state.
Figure 1. State Transition Table
DEFAULT INPUT CHANNEL:
NO
NO
IN
DATA OUTPUT/INPUT
POWER-ON RESET
+
ACKNOWLEDGE
= CH0, IN
CONVERSION
OR READ
24 BITS
SLEEP
STOP
YES
YES
–
= CH1
2497 F01
2
C interface.
The device will not acknowledge an external request dur-
ing the conversion state. After a conversion is fi nished,
the device is ready to accept a read/write request. Once
the LTC2497 is addressed for a read operation, the device
begins outputting the conversion result under the control
of the serial clock (SCL). There is no latency in the conver-
sion result. The data output is 24 bits long and contains a
16-bit plus sign conversion result. Data is updated on the
falling edges of SCL allowing the user to reliably latch data
on the rising edge of SCL. A new conversion is initiated
by a stop condition following a valid write operation or an
incomplete read operation. The conversion automatically
begins at the conclusion of a complete read cycle (all 24
bits read out of the device).
Ease of Use
The LTC2497 data output has no latency, fi lter settling
delay, or redundant data associated with the conversion
cycle. There is a one-to-one correspondence between the
conversion and the output data. Therefore, multiplexing
multiple analog inputs is straightforward. Each conversion,
immediately following a newly selected input is valid and
accurate to the full specifi cations of the device.
The LTC2497 automatically performs offset and full-scale
calibration every conversion cycle independent of the
input channel selected. This calibration is transparent
to the user and has no effect on the operation cycle de-
scribed above. The advantage of continuous calibration
is extreme stability of offset and full-scale readings with
respect to time, supply voltage variation, input channel,
and temperature drift.
Easy Drive Input Current Cancellation
The LTC2497 combines a high precision, delta-sigma ADC
with an automatic, differential, input current cancellation
front end. A proprietary front end passive sampling network
transparently removes the differential input current. This
enables external RC networks and high impedance sen-
sors to directly interface to the LTC2497 without external
amplifi ers. The remaining common mode input current
is eliminated by either balancing the differential input im-
pedances or setting the common mode input equal to the
LTC2497
11
2497f