LTC2494IUHF#PBF Linear Technology, LTC2494IUHF#PBF Datasheet - Page 32

• Manufacturer Part Number: LTC2494IUHF#PBF
• Description: IC ADC 16BIT W/PGA 38-QFN
• Manufacturer: Linear Technology

Specifications of LTC2494IUHF#PBF

• Number Of Bits: 16
• Sampling Rate (per Second): 15
• Data Interface: MICROWIRE™, Serial, SPI™
• Number Of Converters: 1
• Power Dissipation (max): 480µW
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 38-WFQFN, Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

applications inForMation
LTC2494
In addition to the reference sampling charge, the reference
ESD projection diodes have a temperature dependent leak-
age current. This leakage current, nominally 1nA (±10nA
max) results in a small gain error. A 100Ω reference
resistance will create a 0.5µV full-scale error.
Normal Mode Rejection and Anti-Aliasing
One of the advantages delta-sigma ADCs offer over
conventional ADCs is on-chip digital filtering. Combined
with a large oversample ratio, the LTC2494 significantly
simplifies anti-aliasing filter requirements. Additionally,
the input current cancellation feature allows external low
pass filtering without degrading the DC performance of
the device.
The SINC
rejection at all frequencies except DC and integer multiples
of the modulator sampling frequency (f
19 and 20). The modulator sampling frequency is f
15,360Hz while operating with its internal oscillator and
f
of frequency F
When using the internal oscillator, the LTC2494 is designed
to reject line frequencies. As shown in Figure 21, rejec-
tion nulls occur at multiples of frequency f
determined by the input control bits FA and FB (f
or 60Hz or 55Hz for simultaneous rejection). Multiples of
the modulator sampling rate (f
to 15dB (see Figure 22), if noise sources are present at
these frequencies anti-aliasing will reduce their effects.

S
= F
EOSC
Figure 19. Input Normal Mode Rejection, Internal
Oscillator and 50Hz Rejection Mode
4
–100
–110
–120
/20 when operating with an external oscillator
–10
–20
–30
–40
–50
–60
–70
–80
–90
digital filter provides excellent normal mode
0
0 f
DIFFERENTIAL INPUT SIGNAL FREQUENCY (Hz)
EOSC
S
2f
.
S
3f
S
4f
S
5f
S
6f
S
S
7f
= f
S
8f
N
S
• 256) only reject noise
9f
S
10f
S
11f
2494 F19
S
S
12f
) (see Figures
N
, where f
S
N
= 50Hz
N
S
is
=
Figure 22. Input Normal Mode Rejection at f
Figure 20. Input Normal Mode Rejection, Internal
Oscillator and 60Hz Rejection Mode
Figure 21. Input Normal Mode Rejection at DC
–100
–110
–120
–100
–110
–120
–100
–110
–120
–10
–20
–30
–40
–50
–60
–70
–80
–90
–10
–20
–30
–40
–50
–60
–70
–80
–90
–10
–20
–30
–40
–50
–60
–70
–80
–90
0
0
250f
0
0
0
DIFFERENTIAL INPUT SIGNAL FREQUENCY (Hz)
N
f
f
S
N
252f
INPUT SIGNAL FREQUENCY (Hz)
INPUT SIGNAL FREQUENCY (Hz)
2f
N
2f
S
N
254f
3f
S
3f
N
N
4f
S
256f
4f
5f
N
S
N
6f
5f
258f
S
N
f
N
7f
N
= f
6f
S
N
EOSC/5120
260f
8f
S
7f
N
N
9f
2494 F20
S
2494 F21
262f
8f
2494 F22
10f
N
S
S
N
= 256 • f
N
2494fd