LTC2410
20
APPLICATIO S I FOR ATIO
WU
U
frequency fEOSC, then tEOCtest is 3.6/fEOSC. If CS is pulled
HIGH before time tEOCtest, the device remains in the sleep
state. The conversion result is held in the internal static
shift register.
If CS remains LOW longer than tEOCtest, the first rising
edge of SCK will occur and the conversion result is serially
shifted out of the SDO pin. The data output cycle begins on
this first rising edge of SCK and concludes after the 32nd
rising edge. Data is shifted out the SDO pin on each falling
edge of SCK. The internally generated serial clock is output
to the SCK pin. This signal may be used to shift the
conversion result into external circuitry. EOC can be
latched on the first rising edge of SCK and the last bit of the
conversion result on the 32nd rising edge of SCK. After the
32nd rising edge, SDO goes HIGH (EOC = 1), SCK stays
HIGH and a new conversion starts.
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 and 32nd rising edge
of SCK, see Figure 9. On the rising edge of CS, the device
aborts the data output state and immediately initiates a
new conversion. This is useful for systems not requiring
all 32 bits of output data, aborting an invalid conversion
cycle, or synchronizing the start of a conversion. If CS is
pulled HIGH while the converter is driving SCK LOW, the
internal pull-up is not available to restore SCK to a logic
HIGH state. This will cause the device to exit the internal
serial clock mode on the next falling edge of CS. This can
be avoided by adding an external 10k pull-up resistor to
the SCK pin or by never pulling CS HIGH when SCK is LOW.
Whenever SCK is LOW, the LTC2410’s internal pull-up at
pin SCK is disabled. Normally, SCK is not externally driven
if the device is in the internal SCK timing mode. However,
certain applications may require an external driver on SCK.
If this driver goes Hi-Z after outputting a LOW signal, the
LTC2410’s internal pull-up remains disabled. Hence, SCK
remains LOW. On the next falling edge of CS, the device is
switched to the external SCK timing mode. By adding an
external 10k pull-up resistor to SCK, this pin goes HIGH
once the external driver goes Hi-Z. On the next CS falling
edge, the device will remain in the internal SCK timing
mode.
Figure 9. Internal Serial Clock, Reduced Data Output Length
SDO
SCK
(INTERNAL)
CS
>tEOCtest
MSB
SIG
BIT 8
TEST EOC
BIT 27
BIT 26
BIT 28
BIT 29
BIT 30
EOC
BIT 31
EOC
BIT 0
SLEEP
DATA OUTPUT
Hi-Z
DATA OUTPUT
CONVERSION
SLEEP
2410 F09
<tEOCtest
VCC
10k
= 50Hz REJECTION
= EXTERNAL OSCILLATOR
= 60Hz REJECTION
VCC
TEST EOC
VCC
FO
REF+
REF–
SCK
IN+
IN–
SDO
GND
CS
214
3
4
13
5
6
12
1, 7, 8, 9, 10, 15, 16
11
REFERENCE
VOLTAGE
0.1V TO VCC
ANALOG INPUT RANGE
–0.5VREF TO 0.5VREF
3-WIRE
SPI INTERFACE
1
F
2.7V TO 5.5V
LTC2410