LTC2379CDE-18 LINEAR [Linear Integrated Systems], LTC2379CDE-18 Datasheet - Page 13

• Manufacturer Part Number: LTC2379CDE-18
• Description: LTC2379-1818-Bit, 1.6Msps, Low Power SAR ADC with 101.2dB SNR
• Manufacturer: LINEAR [Linear Integrated Systems]

APPLICATIONS INFORMATION
positive supply to power the LT6350 results in additional
power savings for the entire system.
Figure 9a shows how to configure the LT6350 to accept a
±10V true bipolar input signal and attenuate and level shift
the signal to the reduced input range of the LTC2379-18
when digital gain compression is enabled. Figure 9b shows
an FFT plot with the LTC2379-18 being driven by the LT6350
with digital gain compression enabled.
ADC REFERENCE
The LTC2379-18 requires an external reference to define
its input range. A low noise, low temperature drift refer-
ence is critical to achieving the full datasheet performance
of the ADC. Linear Technology offers a portfolio of high
performance references designed to meet the needs of
10μF
Figure 9a. LT6350 Configured to Accept a ±10V Input Signal While Running Off of a
Single 5.5V Supply When Digital Gain Compression Is Enabled in the LTC2379-18
–10V
10V
Figure 8. Input Swing of the LTC2379 with Gain
Compression Enabled
0V
1k
1k
6.04k
4.32k
V
CM
10μF
4.5V
0.5V
CNV
5V
0V
R
IN
= 15k
LT6350
8
1
PERIOD
IDLE
3.01k
+
–
5.5V
V
R
+
INT
3
V
CM
2
R
INT
–
+
Figure 10. CNV Waveform Showing Burst Sampling
237918 F08
V
–
4
5
6
OUT1
OUT2
5V
4.5V
0.5V
4.5V
0.5V
3300pF
20Ω
20Ω
many applications. With its small size, low power and
high accuracy, the LTC6655-5 is particularly well suited for
use with the LTC2379-18. The LTC6655-5 offers 0.025%
(max) initial accuracy and 2ppm/°C (max) temperature
coefficient for high precision applications. The LTC6655-5
is fully specified over the H-grade temperature range and
complements the extended temperature operation of the
LTC2379-18 up to 125°C. We recommend bypassing the
LTC6655-5 with a 47μF ceramic capacitor (X5R, 0805 size)
close to the REF pin.
The REF pin of the LTC2379-18 draws charge (Q
the 47μF bypass capacitor during each conversion cycle.
The reference replenishes this charge with a DC current,
I
I
the LTC2379-18 is used to continuously sample a signal
at a constant rate, the LTC6655-5 will keep the deviation
of the reference voltage over the entire code span to less
than 0.5LSBs.
When idling, the REF pin on the LTC2379-18 draws only
a small leakage current (< 1μA). In applications where a
burst of samples is taken after idling for long periods as
shown in Figure 10, I
REF
REF
3300pF
3300pF
47μF
, depends on the sampling rate and output code. If
= Q
IN
IN
CONV
+
–
PERIOD
REF
IDLE
LTC2379-18
V
V
V
/t
IN
OUT_F
OUT_S
REF/DGC
CYC
2.5V
V
237918 F09a
LTC6655-5
DD
. The DC current draw of the REF pin,
REF
quickly goes from approximately
–100
–120
–140
–160
–180
–20
–40
–60
–80
Figure 9b. 32k Point FFT Plot
with f
in Figure 9a
0
0
100 200 300 400
IN
LTC2379-18
= 2kHz for Circuit Shown
FREQUENCY (kHz)
237918 F10
500
CONV
SNR = 99dB
THD = –95dB
SINAD = 94.6dB
SFDR = 96.3dB
600
13
) from
237918fa
700
237918 F09b
800