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LTC2311-16

231116fa

For more information www.linear.com/LTC2311-16

APPLICATIONS INFORMATION

OVERVIEW

The LTC2311-16 is a low noise, high speed 16-bit succes-

sive approximation register (SAR) ADC with differential

inputs and a wide input common mode range. Operating

from a single 3.3V or 5V supply, the LTC2311-16 has an

8VP-P differential input range, making it ideal for applica-

tionswhichrequireawidedynamicrange.The LTC2311-16

achieves ±3LSB INL typical, no missing codes at 16 bits

and 81dB SNR typical.

The LTC2311-16 has an onboard reference buffer and low

drift (20ppm/°C max) 4.096V temperature-compensated

reference. The LTC2311-16 also has a high speed SPI-

compatible serial interface that supports CMOS or LVDS.

The fast 5Msps throughput with one-cycle latency makes

the LTC2311-16 ideally suited for a wide variety of high

speedapplications.TheLTC2311-16dissipatesonly50mW

operating at a 5V supply. Nap and sleep modes are also

providedtoreducethepowerconsumptionoftheLTC2311-

16 during inactive periods for further power savings.

CONVERTER OPERATION

The LTC2311-16 operates in two phases. During the

acquisition phase, the sample capacitor is connected to

the analog input pins AIN+ and AIN– to sample the dif-

ferential analog input voltage, as shown in Figure 3. A

falling edge on the CNV pin initiates a conversion. Dur-

ing the conversion phase, the 16-bit CDAC is sequenced

through a successive approximation algorithm for each

input SCK pulse, effectively comparing the sampled input

with binary-weighted fractions of the reference voltage

(e.g., VREFOUT/2, VREFOUT/4 … VREFOUT/65536) using a

differentialcomparator.Attheendofconversion,theCDAC

output approximates the sampled analog input. The ADC

control logic then prepares the 16-bit digital output code

for serial transfer.

TRANSFER FUNCTION

The LTC2311-16 digitizes the full-scale voltage of 2 ×

REFOUT into 216 levels, resulting in an LSB size of

125µV with REFOUT = 4.096V. The ideal transfer function

is shown in Figure 2. The output data is in 2’s comple-

ment format.

Analog Input

The differential inputs of the LTC2311-16 provide great

flexibility to convert a wide variety of analog signals with

no configuration required. The LTC2311-16 digitizes the

difference voltage between the AIN+ and AIN– pins while

supporting a wide common mode input range. The analog

input signals can have an arbitrary relationship to each

other, provided that they remain between VDD and GND.

The LTC2311-16 can also digitize more limited classes of

analog input signals such as pseudo-differential unipolar/

bipolarandfullydifferentialwithnoconfigurationrequired.

The analog inputs of the LTC2311-16 can be modeled

by the equivalent circuit shown in Figure 3. The back-to-

back diodes at the inputs form clamps that provide ESD

protection. In the acquisition phase, 10pF (CIN) from the

Figure 2. LTC2311-16 Transfer Function

Figure 3. The Equivalent Circuit for the Differential

Analog Input of the LTC2311-16

INPUT VOLTAGE (V)

–FSR/2

+FSR/2 – 1LSB

231116 F02

011...111

011...110

111...111

100...000

100...001

000...000

000...001

–1

LSB

FSR = +FS – –FS

1LSB = FSR/65535

LSB

RON

BIAS

VOLTAGE

231116 F03

CIN

10pF

VDD

CIN

10pF

VDD

AIN–

AIN+

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