Datasheet

LTC2480
19
2480fd
applicaTions inForMaTion
an external serial clock. If the change occurs during the
conversion state, the result of the conversion in progress
may be outside specifications but the following conver-
sions will not be affected. If the change occurs during the
data output state and the converter is in the Internal SCK
mode, the serial clock duty cycle may be affected but the
serial data stream will remain valid.
Table 5 summarizes the duration of each state and the
achievable output data rate as a function of f
O
.
Ease of Use
The LTC2480 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 LTC2480 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 LTC2480 automatically enters an internal reset state
when the power supply voltage V
CC
drops below ap-
proximately 2V. This feature guarantees the integrity of
the conversion result and of the serial interface mode
selection.
When the V
CC
voltage rises above this critical threshold,
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 LTC2480 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 LTC2480 contains an on-chip PTAT (proportional to
absolute temperature) signal that can be used as a tempera-
ture sensor. The internal PTAT has a typical value of 420mV
at 27°C and is proportional to the absolute temperature
Table 5. LTC2480 State Duration
STATE OPERATING MODE DURATION
CONVERT Internal Oscillator 60Hz Rejection 133ms, Output Data Rate ≤ 7.5 Readings/s for 1x Speed Mode
67ms, Output Data Rate ≤ 15 Readings/s for 2x Speed Mode
50Hz Rejection 160ms, Output Data Rate ≤ 6.2 Readings/s for 1x Speed Mode
80ms, Output Data Rate ≤ 12.5 Readings/s for 2x Speed Mode
50Hz/60Hz Rejection 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
External Oscillator f
O
= External Oscillator
with Frequency f
EOSC
kHz
(f
EOSC
/5120 Rejection)
41036/f
EOSC
s, Output Data Rate ≤ f
EOSC
/41036 Readings/s for
1x Speed Mode
20556/f
EOSC
s, Output Data Rate ≤ f
EOSC
/20556 Readings/s for
2x Speed Mode
SLEEP As Long As CS = HIGH, After a Conversion is Complete
DATA OUTPUT Internal Serial Clock f
O
= LOW/HIGH
(Internal Oscillator)
As Long As CS = LOW But Not Longer Than 0.62ms
(24 SCK Cycles)
f
O
= External Oscillator with
Frequency f
EOSC
kHz
As Long As CS = LOW But Not Longer Than 192/f
EOSC
ms
(24 SCK Cycles)
External Serial Clock with
Frequency f
SCK
kHz
As Long As CS = LOW But Not Longer Than 24/f
SCK
ms
(24 SCK Cycles)