Datasheet
LTC2439-1
8
24391fa
Once CS is pulled LOW, the device exits the low power
mode and enters the data output state. If CS is pulled HIGH
before the first rising edge of SCK, the device returns to the
low power sleep mode and the conversion result is still
held in the internal static shift register. If CS remains LOW
after the first rising edge of SCK, the device begins
outputting the conversion result and inputting channel
selection bits. Taking CS high at this point will terminate
the data output state and start a new conversion. The
channel selection control bits are shifted in through SDI
from the first rising edge of SCK and depending on the
control bits, the converter updates its channel selection
immediately and is valid for the next conversion. The
details of channel selection control bits are described in
the Input Data Mode section. The output data is shifted out
the SDO pin under the control of the serial clock (SCK). The
output data is updated on the falling edge of SCK allowing
APPLICATIO S I FOR ATIO
WUUU
CS
SDO
Hi-Z
SIG(0)
BIT16
MSB B22
CONVERSON RESULT
BIT15 BIT14 BIT13 BIT12 BIT11 BIT6 BIT5 BIT3 BIT2 BIT1
LSB
BIT0BIT4BIT17
SCK
SDI
SLEEP DATA INPUT/OUTPUT
BIT18
EOC
(1) (0) EN SGL A2 A1 A0 DON’T CARE
CONVERSION
24391 F03a
ODD/
SIGN
CONVERSION RESULT
N – 1
ADDRESS
N
ADDRESS
N + 1
ADDRESS
N + 2
OUTPUT
N – 1
OUTPUT
N
OUTPUT
N + 1
SDO
SCK
SDI
OPERATION
Hi-Z
DON’T CARE
CONVERSION N
24391 F03b
CONVERSION N + 1
DON’T CARE
Hi-Z Hi-Z
CONVERSION RESULT
N
CONVERSION RESULT
N + 1
Figure 3b. Typical Operation Sequence
the user to reliably latch data on the rising edge of SCK (see
Figure 3). The data output state is concluded once 19 bits
are read out of the ADC or when CS is brought HIGH. The
device automatically initiates a new conversion and the
cycle repeats. In order to maintain compatibility with
24-/32-bit data transfers, it is possible to clock the
LTC2439-1 with additional serial clock pulses. This results
in additional data bits which are always logic HIGH.
Through timing control of the CS and SCK pins, the
LTC2439-1 offers several flexible modes of operation
(internal or external SCK and free-running conversion
modes). These various modes do not require program-
ming configuration registers; moreover, they do not dis-
turb the cyclic operation described above. These modes of
operation are described in detail in the Serial Interface
Timing Modes section.
Figure 3a. Input/Output Data Timing