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LTC2320-12

Rev B

For more information www.analog.com

APPLICATIONS INFORMATION

OVERVIEW

The LTC2320-12 is a low noise, high speed 12-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 LTC2320-12 has a

4VP-P or 8VP-P differential input range, making it ideal for

applications which require a wide dynamic range. The

LTC2320-12 achieves ±0.25LSB INL typical, no missing

codes at 12 bits and 77dB SNR.

The LTC2320-12 has an onboard reference buffer and low

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

reference. The LTC2320-12 also has a high speed SPI-

compatible serial interface that supports CMOS or LVDS.

The fast 1.5Msps per channel throughput with no latency

makes the LTC2320-12 ideally suited for a wide variety of

high speed applications. The LTC2320-12 dissipates only

20mWperchannel.Napandsleepmodesarealsoprovided

to reduce the power consumption of the LTC2320-12 dur-

ing inactive periods for further power savings.

CONVERTER OPERATION

The LTC2320-12 operates in two phases. During the ac-

quisition phase, the sample capacitor is connected to the

analog input pins AIN+ and AIN– to sample the differential

analoginputvoltage,asshowninFigure 3.Afallingedgeon

the CNV pin initiates a conversion. During the conversion

phase,the12-bitCDACissequencedthroughasuccessive

approximationalgorithmeffectivelycomparingthesampled

input with binary-weighted fractions of the reference volt-

age (e.g., VREFOUT/2, VREFOUT/4 … VREFOUT/32768) using

a differential comparator. At the end of conversion, a CDAC

output approximates the sampled analog input. The ADC

control logic then prepares the 12-bit digital output code

for serial transfer.

TRANSFER FUNCTION

The LTC2320-12 digitizes the full-scale voltage of 2 •

REFOUT into 213 levels, resulting in an LSB size of 1mV

withREFBUF=4.096V.Theidealtransferfunctionisshown

in Figure 2. The output data is in 2’s complement format.

When driven by fully differential inputs, the transfer func-

tion spans 213 codes. When driven by pseudo-differential

inputs, the transfer function spans 212 codes.

Figure 2. LTC2320-12 Transfer Function

Figure 3. The Equivalent Circuit for the Differential

Analog Input of the LTC2320-12

RON

BIAS

VOLTAGE

232012 F03

CIN

10pF

VDD

CIN

10pF

VDD

AIN–

AIN+

INPUT VOLTAGE (V)

–REFOUT

REFOUT – 1LSB

232012 F02

0 1111 1111 1111

0 1111 1111 1110

1 1111 1111 1111

1 0000 0000 0000

1 0000 0000 0001

0 0000 0000 0000

0 0000 0000 0001

–1

LSB

1LSB =

LSB

2 • REFOUT

8192

Table 1. Code Ranges for the Analog Input Operational Modes

MODE

SPAN (VIN+ – VIN–)

MIN CODE

MAX CODE

Fully Differential

–REFOUT to +REFOUT

1 0000 0000 0000

0 1111 1111 1111

Pseudo-Differential Bipolar

–-REFOUT/2 to +REFOUT/2

1 1000 0000 0000

0 0111 1111 1111

Pseudo-Differential Unipolar

0 to REFOUT

0 0000 0000 0000

0 1111 1111 1111

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