LTC2378-16
applicaTions inForMaTion
5V
many applications. With its small size, low power and
highaccuracy, theLTC6655-5isparticularlywellsuitedfor
use with the LTC2378-16. The LTC6655-5 offers ±.±25%
(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
LTC2378-16 up to 125°C. We recommend bypassing the
LTC6655-5witha47µFceramiccapacitor(X5R,±8±5size)
close to the REF pin.
4.5V
0.5V
0V
237816 F08
Figure 80 Input Swing of the 5TC2378 with Gain
Compression Enabled
positive supply to power the LT635± results in additional
power savings for the entire system.
TheREFpinoftheLTC2378-16drawscharge(Q
)from
COIV
Figure 9a shows how to configure the LT635± to accept a
±1±V true bipolar input signal and attenuate and level shift
the signal to the reduced input range of the LTC2378-16
whendigitalgaincompressionisenabled.Figure9bshows
anFFTplotwiththeLTC2378-16beingdrivenbytheLT635±
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 LTC2378-16 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 ±.5LSꢀs.
ADC REFERENCE
The LTC2378-16 requires an external reference to define
its input range. A low noise, low temperature drift refer-
enceiscriticaltoachievingthefulldatasheetperformance
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 LTC2378-16 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 1±, ꢁ quickly goes from approximately
REF
5.5V
V
V
V
LTC6655-5
IN
0
–20
OUT_F
OUT_S
SNR = 95.5dB
THD = –97.6dB
SINAD = 93.8dB
SFDR = 99.5dB
5V
1k
–40
47µF
V
CM
–60
4.5V
0.5V
2.5V
1k
10µF
3
+
–80
V
6800pF
LT6350
OUT1
OUT2
6.04k
4.32k
REF
V
4
DD
LTC2378-16
REF/DGC
–100
–120
–140
–160
–180
+
–
20Ω
IN
IN
R
R
INT
8
+
–
INT
10µF
R
3300pF
20Ω
–
+
5
6
1
4.5V
2
–
237816 F09a
V
6800pF
10V
0V
–10V
= 15k
3.01k
IN
0
100
200
300
400
500
0.5V
V
CM
FREQUENCY (kHz)
237816 F09b
Figure 9a0 5T63.± Configured to Accept a ±1±V Input Signal While Running Off of a
Single .0.V Supply When Digital Gain Compression Is Enabled in the 5TC2378-16
Figure 9b0 32k Point FFT Plot
with fIN = 2kHz for Circuit Shown
in Figure 9a
CNV
IDLE
PERIOD
IDLE
PERIOD
237816 F10
Figure 1±0 CNV Waveform Showing ꢀurst Sampling
237816f
13
LINEAR_DIMENSIONS [ Linear Dimensions ]
