LTC2440IGN#PBF Linear Technology, LTC2440IGN#PBF Datasheet - Page 22

• Manufacturer Part Number: LTC2440IGN#PBF
• Description: IC ADC DIFFER 24-BIT HS 16-SSOP
• Manufacturer: Linear Technology

Specifications of LTC2440IGN#PBF

• Number Of Bits: 24
• Sampling Rate (per Second): 3.5k
• Data Interface: MICROWIRE™, Serial, SPI™
• Number Of Converters: 2
• Power Dissipation (max): 40mW
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP (0.150", 3.90mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

LTC2440
APPLICATIONS INFORMATION
LTC2440 Input Structure
Modern delta sigma converters have switched capacitor
front ends that repeatedly sample the input voltage over
some time period. The sampling process produces a small
current pulse at the input and reference terminals as the
capacitors are charged. The LTC2440 switches the input
and reference to a 5pF sample capacitor at a frequency
of 1.8MHz. A simplifi ed equivalent circuit is shown in
Figure 16.
The average input and reference currents can be expressed
in terms of the equivalent input resistance of the sample
capacitor, where:
22
CONVERTER
Req = 1/(f
CURRENT
SUPPLY
STATE
CS
SW
• Ceq)
SLEEP
8μA
SWITCHING FREQUENCY
f
f
SW
SW
V
V
I
V
V
I
DATA
REF
REF
I
I
REF
REF
OUT
IN
IN
IN
IN
= 1.8MHz INTERNAL OSCILLATOR
= f
+
+
–
–
+
+
–
–
EOSC
V
V
CC
CC
/5 EXTERNAL OSCILLATOR
8mA
CONVERT
V
V
I
I
I
I
LEAK
LEAK
LEAK
LEAK
Figure 15. Reduced Power Timing Mode
CC
CC
Figure 16. LTC2440 Input Structure
I
I
I
I
LEAK
LEAK
LEAK
LEAK
R
R
R
R
SW
SW
SW
SW
500Ω
500Ω
500Ω
500Ω
(TYP)
(TYP)
(TYP)
(TYP)
When using the internal oscillator, f
equivalent resistance is approximately 110kΩ.
Driving the Input and Reference
Because of the small current pulses, excessive lead length
at the analog or reference input may allow refl ections or
ringing to occur, affecting the conversion accuracy. The
key to preserving the accuracy of the LTC2440 is complete
settling of these sampling glitches at both the input and
reference terminals. There are several recommended
methods of doing this.
2440 F16
SLEEP
8μA
C
5pF
(TYP)
(C
EQ
EQ
= 3.5pF SAMPLE CAP + PARASITICS)
DATA
OUT
8μA
CONVERT
SW
is 1.8MHz and the
8mA
SLEEP
2440 F15
2440fd