ltc2435-1 Linear Technology Corporation, ltc2435-1 Datasheet - Page 22

• 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
LTC2435/LTC2435-1
HIGH). If F
f
time t
conversion result is held in the internal static shift register.
If CS remains LOW longer than t
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 24th
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 24th rising edge of SCK. After the
24th 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 24th rising edge of
SCK, see Figure 12. On the rising edge of CS, the device
aborts the data output state and immediately initiates a
22
EOSC
(INTERNAL)
, then t
EOCtest
SDO
DATA OUTPUT
SCK
CS
O
is driven by an external oscillator of frequency
EOCtest
, the device returns to the sleep state. The
Hi-Z
SLEEP
> t
EOCtest
is 3.6/f
BIT 0
U
EOC
CONVERSION
Hi-Z
EOSC
U
TEST EOC
SLEEP
. If CS is pulled HIGH before
Figure 12. Internal Serial Clock, Reduced Data Output Length
Hi-Z
EOCtest
W
SLEEP
ANALOG INPUT RANGE
, the first rising
Hi-Z
–0.5V
TEST EOC
<t
EOCtest
REF
1, 7, 8, 9, 10, 15, 16
BIT 23
0.1V TO V
REFERENCE
EOC
TO 0.5V
U
VOLTAGE
1μF
2.7V TO 5.5V
REF
CC
BIT 22
2
3
4
5
6
V
REF
REF
IN
IN
GND
CC
LTC2435-1
+
–
LTC2435/
+
–
new conversion. This is useful for systems not requiring
all 24 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 LTC2435/LTC2435-1 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 exter-
nal driver on SCK. If this driver goes Hi-Z after outputting
a LOW signal, the LTC2435/LTC2435-1 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.
BIT 21
SIG
SDO
SCK
CS
F
O
DATA OUTPUT
14
13
12
11
BIT 20
MSB
3-WIRE
SPI INTERFACE
V
BIT 19
CC
= 50Hz REJECTION (LTC2435)
= EXTERNAL OSCILLATOR
= 60Hz REJECTION (LTC2435)
= 50Hz/60Hz REJECTION (LTC2435-1)
BIT 18
BIT 8
V
CONVERSION
CC
Hi-Z
10k
TEST EOC
2435 F12
24351fb