LTC2442
16
2442fb
For more information www.linear.com/LTC2442
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 4.
The serial clock mode is selected by the EXT pin. To select
the external serial clock mode, EXT must be tied low.
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 (BUSY = 1) while a conversion is in progress
and EOC = 0 (BUSY = 0) if the device is in the sleep state.
Independent of CS, the device automatically enters the
sleep state once the conversion is complete.
When the device is in the sleep state (EOC = 0), its con
-
version result is held in an internal static shift register.
The device remains in the sleep state until the first rising
edge of SCK is seen. 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 32nd rising
edge of SCK. On the 32nd falling edge of SCK, the device
begins a new conversion. SDO goes HIGH (EOC = 1) and
BUSY goes HIGH 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
and BUSY monitored for the completion of a conversion.
MSB
BIT 28 BIT 27 BIT 26 BIT 25 BIT 24 BIT 23 BIT 22 BIT 21 BIT 20 BIT 19 BIT 0
LSB
Hi-Z
2442 F04
SIG
BIT 29
“0”
BIT 30
EOC
Hi-Z
CS
SCK
(EXTERNAL)
SDI
SDO
BUSY
BIT 31
1 0 EN SGL 0 0 A0 OSR3 OSR2 OSR1 OSR0 TWOXODD
1 2 3 4 5 6 7 8 9 10 11 12 13 14 32
CONVERSION SLEEP DATA OUTPUT CONVERSION
TEST EOC TEST EOC
V
CC
V
+
+INA
MUXOUTA
BUSY
SDO
SDI
EXT
SCK
F
O
MUXOUTB
+INB
GND
21
6
7
8
9
28
12
13
11
17
18
10
26
25
4, 5, 32
19
27
2
34
REFERENCE
VOLTAGE
0.1V TO V
CC
ANALOG
INPUTS
24
= EXTERNAL OSCILLATOR
= INTERNAL OSCILLATOR
(SIMULTANEOUS 50Hz/60Hz
REJECTION AT 6.9Hz OUTPUT RATE
1µF
0.1µF
4.5V TO 5.5V V
CC
TO 15V
LTC2442
1µF
0.1µF
CS
4-WIRE
SPI INTERFACE
–15V TO GND
V
–
REF
+
REF
–
OUTB
–INB
ADCINB
OUTA
–INA
ADCINA
CH0
CH1
CH2
CH3
COM
29
30
31
3
33
1
36
35
Figure 4. External Serial Clock, Single Cycle Operation
APPLICATIONS INFORMATION
