LT6236 datasheet(26/50 Pages) LINER

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LTC2372-16

237216f

For more information www.linear.com/LTC2372-16

Figure 11c. 32k Point FFT fSMPL = 500ksps, fIN = 1kHz for

Circuit Shown in Figure 11b

ADC REFERENCE

There are three ways of providing the ADC reference. The

first is to use both the internal reference and reference

buffer. The second is to externally overdrive the internal

reference and use the internal reference buffer. The third

is to disable the internal reference buffer and overdrive

the REFBUF pin from an external source. The following

tables give examples of these cases and the resulting fully

differential, unipolar and bipolar input ranges.

Table 2. Internal Reference with Internal Buffer

REFIN

REFBUF

FULLY

DIFFERENTIAL

INPUT RANGE

UNIPOLAR

INPUT RANGE

BIPOLAR

INPUT RANGE

2.048V

4.096V

±4.096V

0V to 4.096V

±2.048V

Table 3. External Reference with Internal Buffer

REFIN

(OVERDRIVE)

REFBUF

FULLY

DIFFERENTIAL

INPUT RANGE

UNIPOLAR

INPUT RANGE

BIPOLAR

INPUT RANGE

1.25 (Min)

2.5V

±2.5V

0V to 2.5V

±1.25V

2.048V

4.096V

±4.096V

0V to 4.096V

±2.048V

2.4V (Max)

4.8V

±4.8V

0V to 4.8V

±2.4V

Table 4. External Reference Unbuffered

REFIN

REFBUF

FULLY

DIFFERENTIAL

INPUT RANGE

UNIPOLAR

INPUT RANGE

BIPOLAR

INPUT RANGE

2.5V (Min)

±2.5V

0V to 2.5V

±1.25V

5V (Max)

±5V

0V to 5V

±2.5V

applicaTions inForMaTion

Figure 12a. LTC2372-16 Internal Reference Circuit

237216 F12a

47µF

6.5k

15k

LTC2372-16

REFERENCE

BUFFER

REFBUF

REFIN

GND

BANDGAP

REFERENCE

6.5k

0.1µF

237216 F12b

47µF

6.5k

15k

LTC2372-16

REFERENCE

BUFFER

REFBUF

REFIN

GND

BANDGAP

REFERENCE

6.5k

2.7µF

LTC6655-2.048

Internal Reference with Internal Buffer

The LTC2372-16 has an on-chip, low noise, low drift

(20ppm/°C), temperature compensated bandgap refer-

ence that is factory trimmed to 2.048V. It is internally

connected to a reference buffer as shown in Figure 12a

and is available at REFIN (Pin 13). REFIN should be by-

passed to GND with a 0.1μF ceramic capacitor to minimize

noise. The reference buffer gains the REFIN voltage by 2

to 4.096V at REFBUF (Pin 12). Bypass REFBUF to GND

with at least 47μF ceramic capacitor (X7R, 10V, 1210 size)

to compensate the reference buffer and minimize noise.

Figure 12b. Using the LTC6655-2.048 as an External Reference

SNR = 94dB

THD = –105.3dB

SINAD = 93.7dB

SFDR = 108dB

FREQUENCY (kHz)

100

150

200

250

–180

–160

–140

–120

–100

–80

–60

–40

–20

237216 F11c

External Reference with Internal Buffer

If more accuracy and/or lower drift is desired, REFIN

can be easily overdriven by an external reference since a

15k resistor is in series with the reference as shown in

Figure 12b. REFIN can be overdriven in the range from

1.25V to 2.4V. The resulting voltage at REFBUF will be

2 × REFIN. Linear Technology offers a portfolio of high

performance references designed to meet the needs of

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