LTC2420CS8 Linear Technology, LTC2420CS8 Datasheet - Page 21

• Manufacturer Part Number: LTC2420CS8
• Description: IC ADC 20BIT MICRPWR W/OSC 8SOIC
• Manufacturer: Linear Technology

Specifications of LTC2420CS8

• Number Of Bits: 20
• Sampling Rate (per Second): 7.5
• Data Interface: MICROWIRE™, Serial, SPI™
• Number Of Converters: 2
• Power Dissipation (max): 1mW
• Voltage Supply Source: Single Supply
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: Q1156784

APPLICATIO S I FOR ATIO
capacitor tied to CS, see Figure 12. The time the converter
spends in the sleep state is determined by the value of the
external timing capacitor, see Figures 13 and 14. Once the
voltage at CS falls below an internal threshold ( 1.4V), the
device automatically begins outputting data. The data
output cycle begins on the first rising edge of SCK and
ends on 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.
After the 24th rising edge, CS is pulled HIGH and a new
conversion is immediately started. This is useful in appli-
cations requiring periodic monitoring and ultralow power.
Figure 15 shows the average supply current as a function
of capacitance on CS.
It should be noticed that the external capacitor discharge
current is kept very small in order to decrease the con-
verter power dissipation in the sleep state. In the autostart
mode the analog voltage on the CS pin cannot be observed
(INTERNAL)
GND
SDO
SCK
V
CS
CC
U
CONVERSION
U
Hi-Z
W
Figure 12. Internal Serial Clock, Autostart Operation
–0.12V
SLEEP
REF
TO 1.12V
0.1V TO V
U
1 F
2.7V TO 5.5V
V
REF
REF
V
CC
IN
BIT 23
EOC
V
V
V
GND
CC
REF
IN
without disturbing the converter operation using a regular
oscilloscope probe. When using this configuration, it is
important to minimize the external leakage current at the
CS pin by using a low leakage external capacitor and
properly cleaning the PCB surface.
LTC2420
BIT 22
SDO
SCK
CS
F
O
DATA OUTPUT
7
6
5
4
3
1
0
BIT 21
2
Figure 13. CS Capacitance vs f
SIG
1
C
EXT
10
V
CC
CAPACITANCE ON CS (pF)
= 50Hz REJECTION
= EXTERNAL OSCILLATOR
= 60Hz REJECTION
100
1000
BIT 0
V
CC
= 5V
10000
V
CC
CONVERSION
SAMPLE
2420 F13
= 3V
100000
LTC2420
Hi-Z
2420 F12
21