LTC2379-18
APPLICATIONS INFORMATION
5V
many applications. With its small size, low power and
highaccuracy, theLTC6655-5isparticularlywellsuitedfor
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
LTC6655-5witha47μFceramiccapacitor(X5R,0805size)
close to the REF pin.
4.5V
0.5V
0V
237918 F08
Figure 8. Input Swing of the ꢀTC2379 with Gain
Compression Enabled
positive supply to power the LT6350 results in additional
power savings for the entire system.
TheREFpinoftheLTC2379-18drawscharge(Q
)from
COIV
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
whendigitalgaincompressionisenabled.Figure9bshows
anFFTplotwiththeLTC2379-18beingdrivenbytheLT6350
with digital gain compression enabled.
the 47μF bypass capacitor during each conversion cycle.
The reference replenishes this charge with a DC current,
ꢁ
ꢁ
= Q
/t . The DC current draw of the REF pin,
REF
REF
COIV CYC
, depends on the sampling rate and output code. ꢁf
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 0.5LSꢀs.
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
When idling, the REF pin on the LTC2379-18 draws only
a small leakage current (< 1μA). ꢁn applications where a
burst of samples is taken after idling for long periods as
shown in Figure 10, ꢁ quickly goes from approximately
REF
5.5V
V
V
V
LTC6655-5
ꢁI
0
–20
OUT_F
OUT_S
SIR = 99dꢀ
5V
THD = –95dꢀ
SꢁIAD = 94.6dꢀ
SFDR = 96.3dꢀ
1k
–40
47μF
V
CM
–60
4.5V
0.5V
2.5V
1k
10μF
3
+
–80
V
3300pF
LT6350
OUT1
OUT2
6.04k
4.32k
REF
V
4
DD
LTC2379-18
REF/DGC
–100
–120
–140
–160
–180
+
–
20Ω
ꢁI
R
R
ꢁIT
8
+
–
ꢁIT
10μF
R
3300pF
20Ω
ꢁI
–
+
5
6
1
4.5V
2
–
237918 F09a
V
3300pF
10V
0V
–10V
= 15k
3.01k
ꢁI
0
100 200 300 400 500 600 700 800
0.5V
V
CM
FREQUEICY (kHz)
237918 F09b
Figure 9a. ꢀT6350 Configured to Accept a 10V Input Signal While Running Off of a
Single 5.5V Supply When Digital Gain Compression Is Enabled in the ꢀTC2379-18
Figure 9b. 32k Point FFT Plot
with fIN = 2kHz for Circuit Shown
in Figure 9a
CIV
ꢁDLE
PERꢁOD
ꢁDLE
PERꢁOD
237918 F10
Figure 10. CNV Waveform Showing ꢁurst Sampling
237918fa
13
Linear Systems [ Linear Systems ]
