Datasheet

LTC2496
18
2496fb
applicaTions inForMaTion
When the device is in the sleep state, its conversion re-
sult is held in an internal static shift register. The device
remains in the sleep state until the first rising edge of SCK
is seen while CS is LOW. The input data is then shifted
in via the SDI pin on each rising edge of SCK (including
the first rising edge). The channel selection will be used
for the following conversion cycle. If the input channel is
changed during this I/O cycle, the new settings take effect
on the conversion cycle following the data input/output
cycle. The output data is shifted out the SDO pin on each
falling edge of SCK. This enables external circuitry to
latch the output on the rising edge of SCK. EOC can be
latched on the first rising edge of SCK and the last bit of
the conversion result can be latched on the 24th rising
edge of SCK. On the 24th falling edge of SCK, the device
begins a new conversion and SDO goes HIGH (EOC = 1)
indicating a conversion is in progress.
At the conclusion of the data cycle, CS may remain LOW
and EOC monitored as an end-of-conversion interrupt.
Typically, CS remains LOW during the data output/input
state. However, the data output state may be aborted by
pulling CS HIGH any time between the 1st falling edge
and the 24th falling edge of SCK, see Figure 5. On the
rising edge of CS, the device aborts the data output state
and immediately initiates a new conversion. In order to
program a new input channel, 8 SCK clock pulses are
required. If the data output sequence is aborted prior to
the 8th falling edge of SCK, the new input data is ignored
and the previously selected input channel remains valid.
If the rising edge of CS occurs after the 8th falling edge
of SCK, the new input channel is loaded and valid for the
next conversion cycle.
Figure 5. External Serial Clock, Reduced Output Data Length and Valid Channel Selection
10µF
0.1µF
2.7V TO 5.5V
Hi-Z
2496 F05
CS
SCK
(EXTERNAL)
SDI
SDO
CONVERSION SLEEP DATA INPUT/OUTPUT SLEEPCONVERSION
V
CC
f
O
REF
+
REF
–
CH0
CH7
CH8
CH15
COM
SCK
SDI
SDO
CS
GND
28 35
29
30
8
15
16
23
7
38
37
1,3,4,5,6,31,32,33,39
36
34
REFERENCE
VOLTAGE
0.1V TO V
CC
ANALOG
INPUTS
= EXTERNAL OSCILLATOR
= INTERNAL OSCILLATOR
LTC2496
4-WIRE
SPI INTERFACE
•
•
•
•
•
•
•
•
•
•
•
•
EOC
BIT 20 BIT 19 BIT 18 BIT 17 BIT 16 BIT 15BIT 21BIT 22BIT 23
1 2 3 4 5 6 7 8
1 0 EN SGL A2 A1 A0ODD
DON'T CAREDON'T CARE
MSBSIG“0”