ltc2484 Linear Technology Corporation, ltc2484 Datasheet - Page 18

• Manufacturer Part Number: ltc2484
• Description: 24-bit Delta Sigma Adc With Easy Drive Input Current Cancellation
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
LTC2484
Table 4. LTC2484 State Duration
STATE
CONVERT
SLEEP
DATA OUTPUT
Ease of Use
The LTC2484 data output has no latency, filter 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 voltages is easy.
The LTC2484 performs offset and full-scale calibrations
every conversion cycle. This calibration is transparent to
the user and has no effect on the cyclic operation described
above. The advantage of continuous calibration is extreme
stability of offset and full-scale readings with respect to time,
supply voltage change and temperature drift.
Power-Up Sequence
The LTC2484 automatically enters an internal reset
state when the power supply voltage V
approximately 2V. This feature guarantees the integrity of
the conversion result and of the serial interface mode
selection.
18
OPERATING MODE
Internal Oscillator
External Oscillator
Internal Serial Clock
External Serial Clock with
Frequency f
U
U
SCK
kHz
W
CC
60Hz Rejection
50Hz Rejection
50Hz/60Hz Rejection
F
with Frequency f
(f
F
(Internal Oscillator)
F
Frequency f
O
O
O
EOSC
drops below
= External Oscillator
= LOW/HIGH
= External Oscillator with
U
/5120 Rejection)
EOSC
EOSC
kHz
kHz
When the V
the converter creates an internal power-on-reset (POR)
signal with a duration of approximately 4ms. The POR
signal clears all internal registers. Following the POR
signal, the LTC2484 starts a normal conversion cycle and
follows the succession of states described in Figure 1. The
first conversion result following POR is accurate within the
specifications of the device if the power supply voltage is
restored within the operating range (2.7V to 5.5V) before
the end of the POR time interval.
On-Chip Temperature Sensor
The LTC2484 contains an on-chip PTAT (proportional to
absolute temperature) signal that can be used as a
temperature sensor. The internal PTAT has a typical value
of 420mV at 27°C and is proportional to the absolute tem-
perature value with a temperature coefficient of
420/(27 + 273) = 1.40mV/°C (SLOPE), as shown in Figure
4. The internal PTAT signal is used in a single-ended mode
referenced to device ground internally. The 1x speed mode
with automatic offset calibration is automatically selected
for the internal PTAT signal measurement as well.
DURATION
133ms, Output Data Rate ≤ 7.5 Readings/s for 1x Speed Mode
67ms, Output Data Rate ≤ 15 Readings/s for 2x Speed Mode
160ms, Output Data Rate ≤ 6.2 Readings/s for 1x Speed Mode
80ms, Output Data Rate ≤ 12.5 Readings/s for 2x Speed Mode
147ms, Output Data Rate ≤ 6.8 Readings/s for 1x Speed Mode
73.6ms, Output Data Rate ≤ 13.6 Readings/s for 2x Speed Mode
41036/f
1x Speed Mode
20556/f
2x Speed Mode
As Long As CS = HIGH, After a Conversion is Complete
As Long As CS = LOW But Not Longer Than 0.83ms
(32 SCK Cycles)
As Long As CS = LOW But Not Longer Than 256/f
(32 SCK Cycles)
As Long As CS = LOW But Not Longer Than 32/f
(32 SCK Cycles)
CC
EOSC
EOSC
voltage rises above this critical threshold,
s, Output Data Rate ≤ f
s, Output Data Rate ≤ f
EOSC
EOSC
/41036 Readings/s for
/20556 Readings/s for
SCK
EOSC
ms
ms
2484fa