Datasheet

LTC2486
23
2486fd
APPLICATIONS INFORMATION
On the falling edge of EOC, the conversion result is load-
ing into an internal static shift register. The output data
can now be shifted out the SDO pin under control of the
externally applied SCK signal. Data is updated on the fall-
ing edge of SCK. The input data is shifted into the device
through the SDI pin on the rising edge of SCK. On the
24th falling edge of SCK, SDO goes HIGH, indicating a
new conversion has begun. This data now serves as EOC
for the next conversion.
Internal Serial Clock, Single Cycle Operation
This timing mode uses the internal serial clock to shift out
the conversion result and CS to monitor and control the
state of the conversion cycle (see Figure 9).
In order to select the internal serial clock timing mode,
the serial clock pin (SCK) must be fl oating or pulled HIGH
before the conclusion of the POR cycle and prior to each
falling edge of CS. An internal weak pull-up resistor is active
on the SCK pin during the falling edge of CS; therefore,
the internal SCK mode is automatically selected if SCK is
not externally driven.
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.
Once CS is pulled LOW, SCK goes LOW and EOC is output
to the SDO pin. EOC = 1 while the conversion is in progress
and EOC = 0 if the device is in the sleep state.
When testing EOC, if the conversion is complete (EOC =
0), the device will exit sleep state. In order to return to the
sleep state and reduce the power consumption, CS must be
pulled HIGH before the device pulls SCK HIGH. When the
device is using its own internal oscillator (f
O
is tied LOW),
the fi rst rising edge of SCK occurs 12μs (t
EOCTEST
= 12μs)
after the falling edge of CS. If f
O
is driven by an external
oscillator of frequency f
EOSC
, then t
EOCTEST
= 3.6/f
EOSC
.
If CS remains LOW longer than t
EOCTEST
, the fi rst rising
edge of SCK will occur and the conversion result is shifted
out the SDO pin on the falling edge of SCK. The serial
input word (SDI) is shifted into the device on the rising
edge of SCK.
After the 24th rising edge of SCK a new conversion au-
tomatically begins. SDO goes HIGH (EOC = 1) and SCK
Figure 9. Internal Serial Clock, Single Cycle Operation
Hi-Z
2486 F09
CS
SCK
(INTERNAL)
SDI
SDO
CONVERSION SLEEP DATA INPUT/OUTPUT
V
CC
f
O
SCK
SDI
GND
REFERENCE
VOLTAGE
0.1V TO V
CC
ANALOG
INPUTS
= EXTERNAL OSCILLATOR
= INTERNAL OSCILLATOR
LTC2486
4-WIRE
SPI INTERFACE
EOC
BIT 20 BIT 19 BIT 18 BIT 17 BIT 16 BIT 15 BIT 14 BIT 13 BIT 12 BIT 11BIT 21BIT 22BIT 23
BIT 10 BIT 9 BIT 0
1 2 3 4 5 6 7 8 9 10111213141516 24
1 0 EN SGL A2 A1 A0 EN2 IM FA FB SPD GS2 GS1 GS0ODD
DON'T CAREDON'T CARE
MSBSIG“0”
OPTIONAL
10k
V
CC
<t
EOCTEST
REF
+
REF
–
CH0
CH1
CH2
CH3
COM
CS
12 1
13
14
8
9
10
11
7
3
4
6
5
2
2.7V TO 5.5V
0.1μF
10μF
SDO
CONVERSION