LTC2602 datasheet(17/26 Pages) LINER

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LTC2321-16

232116fc

For more information www.linear.com/LTC2321-16

applicaTions inForMaTion

External Reference

The internal reference buffer can also be overdriven from

1.25V to 5V with an external reference at REFOUT1,2

as shown in Figure 13 (b and c). To do so, REFINT must

be grounded to disable the reference buffer. A 55k inter-

nal resistance loads the REFOUT1,2 pins when the ref-

erence buffer is disabled. To maximize the input signal

swing and corresponding SNR, the LTC6655-5 is recom-

mended when overdriving REFOUT1,2. The LTC6655-5

offers the same small size, accuracy, drift and extended

temperature range as the LTC6655-4.096. By using a 5V

reference, a higher SNR can be achieved. We recommend

bypassing the LTC6655-5 with a parallel combination of

a 0.1µF (X7R, 0402 size) ceramic capacitor and a 10μF

ceramic capacitor (X5R, 0805 size) close to each of the

REFOUT1,2 and REFRTN1,2 pins.

Internal Reference Buffer Transient Response

The REFOUT1,2 pins of the LTC2321-16 draw charge

(QCONV) from the external bypass capacitors during each

conversion cycle. If the internal reference buffer is over-

driven, the external reference must provide all of this charge

with a DC current equivalent to IREF = QCONV/tCYC.

Thus, the DC current draw of REFOUT1,2 depends

on the sampling rate and output code. In applications

where a burst of samples is taken after idling for long

VDD

LTC2321-16

GND

232116 F13a

3.3V TO 5V

REFOUT2

REFOUT1

REFRTN1

REFRTN2

REFINT

0.1µF

10µF

0.1µF

10µF

VIN

SHDN

VOUT_F

VOUT_S

LTC6655-4.096

LTC2321-16

GND

232116 F13b

5V TO 13.2V

REFOUT2

REFOUT1

REFRTN1

REFRTN2

REFINT

0.1µF

10µF

0.1µF

10µF

VIN

SHDN

VOUT_F

VOUT_S

LTC6655-4.096

VIN

SHDN

VOUT_F

VOUT_S

LTC6655-2.048

LTC2321-16

GND

232116 F13c

5V TO 13.2V

REFOUT2

REFOUT1

REFRTN1

REFRTN2

REFINT

0.1µF

10µF

0.1µF

10µF

(13a) LTC2321-16 Internal Reference Circuit

(13b) LTC2321-16 with a Shared External Reference Circuit

(13c) LTC2321-16 with Different External Reference Voltages

Figure 13.

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