LTC2379-18

13

237918p

–180

–60

–40

–20

–80

–100

–120

–140

–160

0

237918 F09b

SNR = 99dB

THD = –95dB

SINAD = 94.6dB

SFDR = 96.3dB

FREQUENCY (kHz)

0

100 200 300 400

800

700

600

500

Figure 9b. 32k Point FFT Plot

in Figure 9a

Figure 8. Input Swing of the LTC2379 with Gain

Compression Enabled

APPLICATIONS INFORMATION

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

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 47μF bypass capacitor during each conversion cycle.

The reference replenishes this charge with a DC current,

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

0μA to a maximum of 1.2mA at 1.6Msps. This step in DC

CNV

IDLE

PERIOD

IDLE

PERIOD

237918 F10

Figure 10. CNV Waveform Showing Burst Sampling

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

237918 F08

5V

4.5V

0.5V

0V

LT6350

3.01k

4.32k

237918 F09a

OUT1

OUT2

8

4

5

2

1

6

3

+

–

–

+

20Ω

3300pF

20Ω

6.04k

1k

1k

0.5V

4.5V

0.5V

4.5V

5V

5.5V

47μF

10μF

10μF

LTC2379-18

REF/DGC

REF

2.5V

LTC6655-5

–10V

10V

0V

3300pF

3300pF