ltc2435-1 Linear Technology Corporation, ltc2435-1 Datasheet - Page 19

• Manufacturer Part Number: ltc2435-1
• Description: 20-bit No Latency Delta Sigma Adcs With Differential Input And Differential Reference
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
External Serial Clock, Single Cycle Operation
(SPI/MICROWIRE Compatible)
This timing mode uses an external serial clock to shift out
the conversion result and a CS signal to monitor and
control the state of the conversion cycle, see Figure 8.
The serial clock mode is selected on the falling edge of CS.
To select the external serial clock mode, the serial clock pin
(SCK) must be LOW during each CS falling edge.
The serial data output pin (SDO) is Hi-Z as long as CS is
HIGH. At any time during the conversion cycle, CS may be
pulled LOW in order to monitor the state of the converter.
While CS is pulled LOW, EOC is output to the SDO pin.
EOC = 1 while a conversion is in progress and EOC = 0 if
the conversion is over. With CS HIGH, the device auto-
matically enters the sleep state once the conversion is
complete.
When CS is low, the device enters the data output mode.
The result is held in the internal static shift register until
the first SCK rising edge is seen while CS is LOW. 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
(EXTERNAL)
SDO
SCK
CS
Hi-Z
CONVERSION
TEST EOC
SLEEP
U
U
SLEEP
Hi-Z
TEST EOC
Figure 8. External Serial Clock, Single Cycle Operation
BIT 23
W
EOC
BIT 22
ANALOG INPUT RANGE
–0.5V
REF
1, 7, 8, 9, 10, 15, 16
0.1V TO V
REFERENCE
TO 0.5V
U
BIT 21
VOLTAGE
SIG
1μF
2.7V TO 5.5V
REF
CC
BIT 20
MSB
2
3
4
5
6
V
REF
REF
IN
IN
GND
CC
LTC2435-1
+
–
LTC2435/
+
–
BIT 19
latched on the 24th rising edge of SCK. On the 24th falling
edge of SCK, the device begins a new conversion. 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.
Alternatively, CS may be driven HIGH setting SDO to Hi-Z.
As described above, CS may be pulled LOW at any time in
order to monitor the conversion status.
Typically, CS remains LOW during the data output state.
However, the data output state may be aborted by pulling
CS HIGH anytime between the first rising edge and the
24th falling edge of SCK, see Figure 9. On the rising edge
of CS, the device aborts the data output state and imme-
diately initiates a new conversion. This is useful for sys-
tems not requiring all 24 bits of output data, aborting an
invalid conversion cycle or synchronizing the start of a
conversion.
External Serial Clock, 2-Wire I/O
This timing mode utilizes a 2-wire serial I/O interface. The
conversion result is shifted out of the device by an exter-
nally generated serial clock (SCK) signal, see Figure 10. CS
may be permanently tied to ground, simplifying the user
interface or isolation barrier.
SDO
SCK
DATA OUTPUT
CS
F
O
14
13
12
11
BIT 18
3-WIRE
SPI INTERFACE
V
CC
= 50Hz REJECTION (LTC2435)
= EXTERNAL OSCILLATOR
= 60Hz REJECTION (LTC2435)
= 50Hz/60Hz REJECTION (LTC2435-1)
LTC2435/LTC2435-1
BIT 5
BIT 0
LSB
CONVERSION
Hi-Z
TEST EOC
2435 F08
19
24351fb