Datasheet

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LTC1448

Dual 12-Bit Rail-to-Rail

Micropower DAC

–

12-BIT

DAC B

RAIL-TO-RAIL

VOLTAGE

OUTPUTS

12-BIT

DAC A

POWER-ON

RESET

24-BIT

SHIFT

REG

AND

DAC

LATCH

µP

REF

1448 TA01

CLK1

CS/LD3

OUT B

OUT A

GND

2.7V TO 5.5V

Functional Block Diagram: 12-Bit Rail-to-Rail Dual DAC

Differential Nonlinearity

vs Input Code

CODE

–0.5

DNL ERROR (LSB)

–0.4

–0.2

–0.1

0.5

0.2

1024 2048 2560

1448 TA02

–0.3

0.3

0.4

0.1

512 1536 3072 3584 4095

FEATURES

■

SO-8 Package

■

12-Bit Resolution

■

Buffered True Rail-to-Rail Voltage Output

■

External Reference Input Can Be Tied to V

■

Output Swings from 0V to V

REF

■

3V and 5V Supply Operation

■

Schmitt Trigger on Clock Input Allows Direct

Optocoupler Interface

■

Power-On Reset Clears DACs to 0V

■

3-Wire Serial Interface

■

Maximum DNL Error: 0.5LSB

■

Low Cost

The LTC

1448 is a dual rail-to-rail voltage output, 12-bit

digital-to-analog converter (DAC). It includes rail-to-rail

output buffer amplifiers and an easy-to-use 3-wire serial

interface. It is available in 8-pin SO and PDIP packages and

provides the smallest footprint of any dual 12-bit DAC.

The LTC1448 has an external reference input pin (REF)

and its outputs swing from 0V to REF. The REF input can

be tied to V

providing rail-to-rail operation from supplies

of 2.7V to 5.5V. (For devices with internal reference see the

LTC1446 data sheet.) The LTC1448 dissipates 2.5mW

from a 5V supply.

The low power supply current and the small SO-8 package

make the LTC1448 ideal for battery-powered applications.

DESCRIPTION

, LTC and LT are registered trademarks of Linear Technology Corporation.

■

Digital Calibration

■

Industrial Process Control

■

Automatic Test Equipment

■

Cellular Telephones

APPLICATIONS

TYPICAL APPLICATION

Summary of content (12 pages)

PAGE 1
LTC1448 Dual 12-Bit Rail-to-Rail Micropower DAC U DESCRIPTION FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ The LTC®1448 is a dual rail-to-rail voltage output, 12-bit digital-to-analog converter (DAC). It includes rail-to-rail output buffer amplifiers and an easy-to-use 3-wire serial interface. It is available in 8-pin SO and PDIP packages and provides the smallest footprint of any dual 12-bit DAC.
PAGE 2
LTC1448 W U U U W W W ABSOLUTE MAXIMUM RATINGS PACKAGE/ORDER I FOR ATIO VCC to GND .............................................. – 0.5V to 7.5V Logic Inputs to GND ................................ – 0.5V to 7.5V VOUT A, VOUT B, REF to GND ........... – 0.5V to VCC + 0.5V Maximum Junction Temperature .......................... 125°C Operating Temperature Range LTC1448C ............................................ 0°C to 70°C LTC1448I.........................................
PAGE 3
LTC1448 ELECTRICAL CHARACTERISTICS VCC = 2.7V to 5.5V, VOUT A and VOUT B unloaded, REF ≤ VCC, TA = TMIN to TMAX, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS 0.5 1.0 V/µs 14 µs 0.3 nV • s AC Performance Voltage Output Slew Rate Voltage Output Settling Time ● (Notes 2, 3) to ± 0.5LSB Digital Feedthrough Reference Input RIN REF Input Resistance ● 7.5 REF REF Input Range VIH 12.
PAGE 4
LTC1448 U W TYPICAL PERFORMANCE CHARACTERISTICS Minimum Supply Headroom for Full Output Swing vs Load Current Differential Nonlinearity (DNL) 0.5 4 0.4 3 0.3 2 0.2 1 0 –1 –2 0.8 0.6 0.1 0 –0.1 0.5 0.4 0.3 –0.2 –3 –0.3 –4 –0.4 0.2 0.1 0 –0.5 –5 0 512 1024 1536 2048 2560 3072 3584 4095 CODE ∆VOUT < 1LSB CODE: ALL 1’s VOUT = 4.095V 0.
PAGE 5
LTC1448 W BLOCK DIAGRA 12-BIT DAC B LD + DAC B REGISTER CLK 1 8 VOUT B 7 VCC 6 GND 5 VOUT A – 24-BIT SHIFT REGISTER DIN 2 LD CS/LD 3 DAC A REGISTER REF 4 12-BIT DAC A + – POWER-ON RESET 1448 BD WU W TI I G DIAGRA S OPERATING SEQUENCE DAC A INPUT DAC B INPUT MSB LSB MSB DIN D11 D10 D9 D8 D7 D6 CLK 1 2 3 4 5 6 D5 7 D4 D3 8 9 D2 10 D1 11 D0 12 D11 LSB D10 13 14 D9 15 D8 16 D7 D6 17 18 D5 19 D4 20 D3 21 D2 22 D1 D0 23 24 CS/LD (UPDATE
PAGE 6
LTC1448 U U DEFI ITIO S Differential Nonlinearity (DNL): The differerence between the measured change and the ideal 1LSB change for any two adjacent codes. The DNL error between any two codes is calculated as follows: DNL = (∆VOUT – LSB)/LSB where ∆VOUT is the measured voltage difference between two adjacent codes. Digital Feedthrough: The glitch that appears at the analog output caused by AC coupling from the digital inputs when they change state. The area of the glitch is specified in (nV)(sec).
PAGE 7
LTC1448 U W U U APPLICATIONS INFORMATION Rail-to-Rail Output Considerations (FSE) is positive, the output for the highest codes limits at VCC as shown in Figure 1c. No full-scale limiting can occur if VREF is less than VCC – FSE. In any rail-to-rail DAC, the output swing is limited to voltages within the supply range. Offset and linearity are defined and tested over the region of the DAC transfer function where no output limiting can occur.
PAGE 8
LTC1448 U TYPICAL APPLICATIONS This circuit shows how to use one LTC1448 to make an autoranging ADC. The microprocessor sets the reference span and the Common pin for the analog input by loading the appropriate digital code into the LTC1448. VOUT A controls the Common pin for the analog inputs to the LTC1296 and VOUT B controls the reference span by setting the REF + pin on the LTC1296. The LTC1296 has a Shutdown pin that goes low in shutdown mode.
PAGE 9
LTC1448 U TYPICAL APPLICATIONS Digitally Programmable Current Source 5V 0.
PAGE 10
LTC1448 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. N8 Package 8-Lead PDIP (Narrow 0.300) (LTC DWG # 05-08-1510) 0.400* (10.160) MAX 8 7 6 5 1 2 3 4 0.255 ± 0.015* (6.477 ± 0.381) 0.300 – 0.325 (7.620 – 8.255) 0.009 – 0.015 (0.229 – 0.381) ( +0.035 0.325 –0.015 8.255 +0.889 –0.381 ) 0.045 – 0.065 (1.143 – 1.651) 0.065 (1.651) TYP 0.100 ± 0.010 (2.540 ± 0.254) *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
PAGE 11
LTC1448 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. S8 Package 8-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) 0.189 – 0.197* (4.801 – 5.004) 8 7 6 5 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) 1 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 0.053 – 0.069 (1.346 – 1.752) 0°– 8° TYP 0.016 – 0.050 0.406 – 1.270 0.014 – 0.019 (0.355 – 0.483) 2 3 4 0.004 – 0.010 (0.101 – 0.254) 0.050 (1.
PAGE 12
LTC1448 U TYPICAL APPLICATION 12-Bit, 3V to 5V Supply, Dual Voltage Output DAC 2.7V TO 5.5V 0.1µF DIN VCC µP CLK REF VOUT A OUTPUT A 0V TO REF VOUT B OUTPUT B 0V TO REF CS/LD LTC1448 GND 1448 TA03 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC1257 Single 12-Bit VOUT DAC, Full Scale: 2.048V, VCC: 4.75V to 15.75V, Reference Can Be Overdriven Up to 12V, i.e.