LTC2668 datasheet(26/40 Pages) LINER

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LTC2348-16

234816fa

For more information www.linear.com/LTC2348-16

ADC REFERENCE

AsshownpreviouslyinTable1b,theLTC2348-16 supports

three reference configurations. The first uses both the in-

ternalbandgapreferenceandreferencebuffer.Thesecond

externally overdrives the internal reference but retains the

internal buffer, which isolates the external reference from

ADC conversion transients. This configuration is ideal

for sharing a single precision external reference across

multiple ADCs. The third disables the internal buffer and

overdrives the REFBUF pin externally.

Internal Reference with Internal Buffer

The LTC2348-16 has an on-chip, low noise, low drift

(20ppm/°C maximum), temperature compensated band-

gap reference that is factory trimmed to 2.048V. The

reference output connects through a 20kΩ resistor to

the REFIN pin, which serves as the input to the on-chip

reference buffer, as shown in Figure 10a. When employing

the internal bandgap reference, the REFIN pin should be

bypassed to GND (Pin 20) close to the pin with a 0.1μF

ceramic capacitor to filter wideband noise. The reference

buffer amplifies VREFIN to create the converter master

reference voltage VREFBUF = 2 • VREFIN on the REFBUF pin,

nominally 4.096V when using the internal bandgap refer-

ence. Bypass REFBUF to GND (Pin 20) close to the pin with

at least a 47μF ceramic capacitor (X7R, 10V, 1210 size or

X5R, 10V, 0805 size) to compensate the reference buffer,

absorbtransientconversioncurrents,andminimizenoise.

234816 F10a

47µF

6.5k

20k

LTC2348-16

REFERENCE

BUFFER

REFBUF

REFIN

GND

BANDGAP

REFERENCE

6.5k

0.1µF

Figure 10a. Internal Reference with Internal Buffer Configuration

External Reference with Internal Buffer

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

be easily overdriven by an external reference since 20kΩ

of resistance separates the internal bandgap reference

output from the REFIN pin, as shown in Figure 10b. The

valid range of external reference voltage overdrive on the

REFIN pin is 1.25V to 2.2V, resulting in converter mas-

ter reference voltages VREFBUF between 2.5V and 4.4V,

respectively. Linear Technology offers a portfolio of high

performance references designed to meet the needs of

manyapplications.Withitssmallsize,lowpower,andhigh

accuracy,theLTC6655-2.048iswellsuitedforusewiththe

LTC2348-16 when overdriving the internal reference. The

LTC6655-2.048offers0.025%(maximum)initialaccuracy

applicaTions inForMaTion

234816 F10b

47µF

6.5k

20k

LTC2348-16

REFERENCE

BUFFER

REFBUF

REFIN

GND

BANDGAP

REFERENCE

6.5k

2.7µF

LTC6655-2.048

Figure 10b. External Reference with Internal Buffer Configuration

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