Application Note 87 November 2000 Linear …

1 AN87-1 INTRODUCTIONA pplication Note 87 is the fifth in a series that excerptsuseful circuits from Linear technology magazine to pre-serve them for posterity. This Application note highlightsdata conversion, interface and signal conditioning circuitsfrom issue VI:1 (February 1996) through issue VIII:4( November 1998). Like its predecessor, AN67, this Appli-cation Note includes circuits for high speed video, inter-face and hot swap circuits, active RC and switched capaci-tor filter circuitry and a variety of data conversion andinstrumentation circuits. There are also several circuitsthat cannot be so neatly categorized. So, without furtherado, I ll let the authors describe their : Article Titles appear in this Application note exactlyas they originally appeared in Linear technology maga-zine. This may result in some inconsistency in the usageof technology Magazine Circuit Collection, Volume VData Conversion, Interface and Signal Conditioning ProductsRichard Markell, EditorApplication Note 87 November 2000 TABLE OF CONTENTSI ntroduction.

2 1 DATA CONVERTERSThe LTC 1446 and LTC1446L: World s First Dual 12-Bit DACs in SO-8 Packages .. 3 Multichannel A/D Uses a Single Antialiasing Filter .. 4 LTC1454/54L and LTC1458/58L: Dual and Quad 12-Bit, Rail-to-Rail, Micropower DACs .. 5 Micropower ADC and DAC in SO-8 Give PC 12-Bit Analog Interface .. 7 The LTC1594 and LTC1598: Micropower 4- and 8-Channel 12-Bit ADCs .. 10 MUX the LTC1419 Without Software .. 13 The LTC1590 Dual 12-Bit DAC is Extremely Versatile .. 14 New 16-Bit SO-8 DAC Has 1 LSB Max INL and DNL Over Industrial Temperature .. 16 LTC1659, LTC1448: Smallest Rail-to-Rail 12-Bit DACs Have Lowest Power .. 18An SMBus-Controlled 10-Bit, Current Output, 50 A Full-Scale DAC .. 19 INTERFACE CIRCUITSS imple Resistive Surge Protection for Interface Circuits .. 20 The LTC1343 and LTC1344 Form a Software-Selectable Multiple-Protocol Interface PortUsing a DB-25 Connector .. 22 The LT1328: a Low Cost IrDA Receiver Solution for Data Rates up to 4 Mbps .. 34 LTC1387 Single 5V RS232/RS485 Multiprotocol Transceiver.

3 36A 10MB/s Multiple-Protocol Chip Set Supports Net1 and Net2 Standards .. 37 Net1 and Net2 Serial Interface Chip Set Supports Test Mode .. 44 OPERATIONAL AMPLIFIERS/VIDEO AMPLIFIERSLT1490/LT1491 Over-the-Top Dual and Quad Micropower Rail-to-Rail Op Amps .. 46 The LT1210: A 1-Ampere, 35 MHz Current Feedback Amplifier .. 47 The LT1207: An Elegant Dual 60 MHz, 250mA Current Feedback Amplifier .. 50 Application Note 87AN87-2, LTC, and LT are registered trademarks of Linear technology Corporation; Adaptive Power, Burst Mode, C-Load, FilterCAD, No RSENSE, Operational Filter, Over-The-Top, PolyPhase, PowerPathand UltraFast are trademarks of Linear technology Corporation. Gelcell is a trademark of Johnson Controls, Inc.; Kool M is a registered trademark of Magnetics, Inc.; Pentium is a registeredtrademark of Intel Corp.; VERSA-PAC is a trademark of Coiltronics, , Dual and Quad JFET Op Amps Feature C-Load Capabilityand PicoAmpere Input Bias Currents .. 54 The LT1210: High Power Op Amp Yields Higher Voltage and Current.

4 56 New Rail-to-Rail Amplifiers: Precision Performance from Micropower to High Speed .. 59LT1256 Voltage-Controlled Amplitude Limiter .. 61 The LT1495/LT1496: A Rail-to-Rail Op Amps .. 62 Send Camera Power and Video on the Same Coax Cable .. 64200 A, Rail-to-Rail Op Amps Have Over-The-Top Inputs .. 65 Low Distortion Rail-to-Rail Op Amps Have THD with 100kHz Signal .. 66 The LT1167: Precision, Low Cost, Low Power Instrumentation Amplifier Requiresa Single Gain-Set Resistor .. 67 Level Shift Allows CFA Video Amplifier to Swing to Ground on a Single Supply .. 70LT1468: An Operational Amplifier for Fast, 16-Bit Systems .. 71 TELECOMMUNICATIONS CIRCUITSHow to Ring a Phone with a Quad Op Amp .. 73A Low Distortion, Low Power, Single-Pair HDSL Driver Using the LT1497 .. 79 COMPARATORSU ltralow Power Comparators Include Reference .. 80A , 4mA, Single-Supply, Dual Comparator Optimized for 3V/5V Operation .. 82 INSTRUMENTATION CIRCUITSLTC1441-Based Micropower Voltage-to-Frequency Converter.

5 86 Bridge Measures Small Capacitance in Presence of Large Strays .. 87 Water Tank Pressure Sensing, a Fluid Solution .. V/ C Chopped Amplifier Requires Only 5 A Supply Current .. Dual-Comparator-Based Crystal Oscillator has 50% Duty Cycle and Complementary Outputs .. 93 LTC1531 Isolated Comparator .. 94 FILTERSThe LTC1560-1: A 1 MHz/500kHz Continuous-Time, Low Noise, Elliptic Lowpass Filter .. 96 The LTC1067 and LTC1067-50: Universal 4th Order Low Noise, Rail-to-Rail Switched Capacitor Filters .. 98 Universal Continuous-Time Filter Challenges Discrete Designs .. 102 High Clock-to-Center Frequency Ratio LTC1068-200 Extends Capabilities of Switched CapacitorHighpass Filter .. 104 Clock-Tunable, High Accuracy, Quad 2nd Order, Analog Filter Building Blocks .. 106 MISCELLEANEOUSB iased Detector Yields High Sensitivity with Ultralow Power Consumption .. 110 Zero-Bias Detector Yields High Sensitivity with Nanopower Consumption .. 111 Transparent Class-D Amplifiers Featuring the LT1336.

6 112 Single-Supply Random Code Generator .. 118 APPENDIX A: COMPONENT VENDOR CONTACTS .. 120 INDEX .. 123 Application Note 87AN87-3 Data ConvertersTHE LTC1446 AND LTC1446L: WORLD S FIRSTDUAL 12-BIT DACS IN SO-8 PACKAGESby Hassan Malik and Jim BrubakerDual 12-Bit Rail-to-Rail Performance in a Tiny SO-8 The LTC1446 and LTC1446L are dual 12-bit, single-sup-ply, rail-to-rail voltage output digital-to-analog convert-ers. Both of these parts include an internal reference andtwo DACs with rail-to-rail output buffer amplifiers, packedin a small, space-saving 8-pin SO or PDIP package. Apower-on reset initializes the outputs to zero-scale LTC1446 has an output swing of 0V to , makingeach LSB equal to 1mV. It operates from a single supply, dissipating (ICC typical = 700 A). TheLTC1296 VCC47k74HC045V5 VCS22 F PCLK8 ANALOGINPUT CHANNELSDOUTDINCH0 COMSSOREF CH7 REF+ F100 100 LTC1446 F+2N3906 LTC1446L has an output swing of 0V to It canoperate on a single supply with a wide range of It dissipates (ICC typical = 450 A) at a Autoranging 8-Channel ADC with ShutdownFigure 1 shows how to use an LTC1446 to make anautoranging ADC.

7 The microprocessor sets the referencespan and the common pin for the analog input by loadingthe appropriate digital code into the LTC1446. VOUTA controls the common pin for the analog inputs to theLTC1296 and VOUTB controls the reference span by settingthe REF+ pin on the LTC1296. The LTC1296 has a shut-down pin that goes low in shutdown mode. This will turnoff the PNP transistor supplying power to the resistor and capacitor on the LTC1446 outputs act asa lowpass filter for 1. An Autoranging 8-Channel ADC with ShutdownApplication Note 87AN87-4 MULTICHANNEL A/D USESA SINGLE ANTIALIASING FILTERby LTC Applications StaffThe circuit in Figure 3 demonstrates how the LTC1594 sindependent analog multiplexer can simplify the design ofa 12-bit data acquisition system. All four channels areMUXed into a single 1kHz, fourth-order Sallen-Key anti-aliasing filter, which is designed for single-supply opera-tion. Since the LTC1594 s data converter accepts inputsfrom ground to the positive supply, rail-to-rail op ampswere chosen for the filter to maximize dynamic range.

8 TheLT1368 dual rail-to-rail op amp is compensated for F load capacitors (C1 and C2) that help reduce theamplifier s output impedance and improve supply rejec-tion at high frequencies. The filter contributes less than1 LSB of error due to offsets and bias currents. The filter snoise and distortion are less than 72dB for a 100Hz,2VP-P offset sine = 0V(ZERO SCALE) = 2 { VOUTB VOUTA}100k1%10k1% +LT1077 VOUTA = (MID SCALE)VOUTA = (FULL SCALE)TO DIN OF NEXT DACThe combined MUX and A/D errors result in an integralnonlinearity error of 3 LSB (maximum) and a differentialnonlinearity error of (maximum). The typicalsignal-to-noise plus distortion ratio is 68dB, with approxi-mately 78dB of total harmonic distortion. The LTC1594is programmed through a 4-wire serial interface thatallows efficient data transfer to a wide variety of micro-processors and microcontrollers. Maximum serial clockspeed is 200kHz, which corresponds to a sam-pling complete circuit consumes approximately 800 Afrom a single 5V supply.

9 For ratiometric measurements,the A/D s reference can also be taken from the 5V , an external reference should be Wide-Swing, Bipolar-Output DAC withDigitally Controlled OffsetFigure 2 shows how to use an LTC1446 and an LT1077 tomake a wide bipolar-output-swing 12-bit DAC with anoffset that can be digitally programmed. VOUTA, which canbe set by loading the appropriate digital code for DAC A,sets the offset. As this value changes, the transfer curvefor the output moves up and down, as shown in the 2. A Wide-Swing, Bipolar Output DAC with Digitally Controlled OffsetApplication Note 87AN87-5 + +CH0CH1CH2CH3 SHA INVREFCOMGNDVCCMUX FDATA OUTCLOCKDATA INCHIP F1/2LT13681/2LT1368 LTC1454/54L AND LTC1458/58L: DUAL AND QUAD12-BIT, RAIL-TO-RAIL, MICROPOWER DACSby Hassan Malik and Jim BrubakerDual and Quad Rail-to-Rail DACs OfferFlexibility and PerformanceThe LTC1454 and LTC1454L are dual 12-bit, single sup-ply, rail-to-rail voltage-output digital-to-analog convert-ers.

10 The LTC1458 and LTC1458L are quad versions of thisfamily. These DACs have an easy-to-use, SPI-compatibleinterface. A CLR pin and power-on-reset both reset theDAC outputs to zero scale. DNL is guaranteed to be lessthan Each DAC has its own rail-to-rail voltageoutput buffer amplifier. The onboard reference is broughtout to a separate pin and can be connected to the REFHI pins of the DACs. There is also a REFLO pin that can beused to offset the DAC range. For further flexibility the 1/ 2 pin for each DAC allows the user to select a gain ofeither 1 or 2. The LTC1454/54L are available in 16-pinPDIP and SO packages, and the LTC1458/58L are availablein 28-pin SO or SSOP and 3V Single Supply and MicropowerThe LTC1454 and LTC1458 operate from a single supply. The LTC1454 dissipates (ICC typical= 700 A), whereas the LTC1458 dissipates (ICCtypical = ). There is an onboard reference of a nominal full scale of when using the onboardreference and a gain-of-2 LTC1454L and LTC1458L operate on a single supplywith a wide range of to The LTC1454L dissi-pates (ICC typical = 450 A), whereas the LTC1458 Ldissipates (ICC typical = 800 A) from a 3V is a onboard reference and a convenient fullscale of when using the onboard reference and again-of-2 Allows a Host of ApplicationsThese products can be used in a wide range of applica-tions, including digital calibration, industrial process con-trol, automatic test equipment, cellular telephones andportable, battery-powered 3.