LinearTechnologyChronicle A Showcase of Linear Technology's Focus Products Product of the Month LTC2400: A Stand-Alone 24-Bit ADC in SO-8 Package Delivers 10ppm Total Unadjusted Error While Drawing Only 200A Linear Technology brings you the industry's smallest and easiest to use 24-bit ADC--the LTC(R)2400. Its internal low drift oscillator and sinc4 digital filter give 120dB of 50Hz or 60Hz rejection without the need for a precision crystal or external clock. The LTC2400 is intended for DC measurements delivering 24-bit no missing codes and 10ppm Total Unadjusted Error (TUE) over both 2.7V to 5.5V supply and - 40C to 85C temperature variations. Low noise of 0.3ppm (RMS) and 2ppm INL performance combine with 1ppm offset and 4ppm fullscale error to meet the most demanding DC measurement applications. Rejection of 50Hz or 60Hz is accomplished with a single pin. Packaged in an 8-pin SO, the LTC2400 supply current is a low 200A while performing conversions and automatically reduces to 20A for the data transfer cycle and while waiting for the next conversion command. The LTC2400 delivers unparalleled accuracy in a small, easy-to-use package. It gets better. The LTC2400 uses a unique 4th order sinc filter that settles in a single conversion with a one-to-one correspondence between the analog input and the conversion result. This greatly simplifies multiplexed applications by providing accurate conversion results on the first conversion after channel selection. The LTC2400 performs autocalibration of offset and gain errors during each conversion transparently to the user. No need to flush digital filters and manage complicated status registers here. The converter operates on a "convert command" and outputs a 24-bit Vol. 7 No. 12 answer. The analog input range extends 12.5% below ground and above VREF while still providing accurate results. This range allows measurement of signals below ground. The accuracy of the LTC2400 eliminates the need for a PGA to increase resolution in most applications. The reference input can be any value between 0.1V and VCC allowing direct digitization of a wide variety of sensors. The on-chip oscillator can be defeated and an external clock source applied to set a user-defined rejection frequency and output rate. Communication with the LTC2400 is accomplished over an easy-to-use SPI compatible serial interface. Total Unadjusted Error vs Output Code 5 VDD = 5V VREF = 4.5V TA = 25C FO = LOW 4 LINEARITY ERROR (ppm) December 1998 3 2 1 0 -1 -2 -3 -4 -5 0 8,338,608 OUTPUT CODE (DECIMAL) 16,777,215 2400 TA02 LTC2400 Complete Easy-to-Use 24-Bit Analog-to-Digital Converter in SO-8 Package 2.7V TO 5.5V VCC 1F VCC FO = INTERNAL OSC/50Hz REJECTION = EXTERNAL CLOCK SOURCE = INTERNAL OSC/60Hz REJECTION LTC2400 REFERENCE VOLTAGE 0.1V TO 0.9 x VCC ANALOG INPUT RANGE -0.12VREF TO 1.12VREF VREF SCK VIN SDO GND 3-WIRE SPI INTERFACE CS 2400 TA01 Inside This Issue: LT1676/LT1776: Wide Input Range Step-Down Switching Regulators ................................... 2 LTC1627: High Efficiency 500mA Step-Down Switcher Operates from 1- or 2-Cell Li-Ion Batteries ................................................................................................. 2 LTC1650: 16-Bit Voltage Output DAC Now Available for 5V Supply Systems ...................... 3 LT1786F: SMBus Programmable Backlight Supply ................................................................ 3 LTC1694: SMBus Accelerator Improves Data Integrity .......................................................... 4 LTC1597: Ultra-Accurate 16-Bit DAC with On-Chip 4-Quadrant Resistors ............................ 4 Linear Technology Chronicle * December 1998 Applications for the LTC2400 will benefit from the compact, easy-to-use design. Such uses include DC voltage and current measurement, gas analysis, weigh scales, temperature measurements, portable handheld instrumentation and DC multiplexed data acquisition. The small size, SO-8 package will allow next generation designs to be realized with unprecedented form factors and accuracy. A complete demonstration board and samples are available today. Contact your local Linear Technology sales office for a data sheet and evaluation samples. For more information, visit our web site at www.linear-tech.com. , LTC and LT are registered trademarks of Linear Technology Corporation. 1 LT1676/LT1776: Wide Input Range Step-Down Switching Regulators For Automotive, "Fire Wire," 48V Telecom and Cell Phone Chargers The LT(R)1676 and LT1776 are new switching regulators for high efficiency stepdown regulation from up to 60V inputs. The circuits are pin-for-pin compatible and virtually identical. The difference is their internal oscillator frequencies--100kHz for the LT1676 and 200kHz for the LT1776. Both circuits operate at fixed frequency and can be synchronized to higher switching frequencies. The internal switch is capable of up to 500mA output current. The input voltage range is 7.4V to 60V. Maintaining high efficiency in the upper portion of this range requires very fast output switch edge rates. The LT1676/LT1776 contain specialized circuitry to provide this performance. Other circuitry monitors output load level and reduces leading-edge switch rate when the output load is light. This function helps avoid pulse skipping at light loads and the consequent subharmonic behavior. Along with true current mode operation, the LT1676/LT1776 include microampere shutdown and undervoltage lockout functions in 8-pin SO and PDIP packages. Burst ModeTM operation for higher efficiency at lower load currents may be implemented using an external comparator. Dual-output SEPIC and positive-to-negative conversion topologies are also directly supported. (See Linear Technology magazine, November 1998.) The LT1776 is favored for its higher switching frequency that allows for a smaller inductor. However, the higher frequency means increased AC switching losses and thus higher thermal dissipation, so that the LT1676 may be preferred for many uses. The LT1676 can operate continuously at high loads at 60V while the LT1776 is limited to 40V in a continuous high output condition. Figure 1 shows a minimum component count circuit using the LT1676. The circuit produces 5V at up to 500mA output with input voltages in the range of 12V to 48V. No pulse skipping is observed even with no external load. These circuits are perfect for automotive systems including the new 42V standard, for IEEE 1394 "Fire Wire" with its unregulated 8V to 40V power, for battery charging from a wide input range source, and for step-down from the 48V rail in telecom systems. LTC provides other 60V input voltage range switching regulators and controllers for output currents up to 50A. Burst Mode is a trademark of Linear Technology Corporation. 90 C1 39F 63V 1 C5 100pF 5 VIN SHDN 2 VCC VSW LT1676 C1:PANASONIC HFQ (201) 348-7522 C2: AVX D CASE TPSD107M010R0080 (803) 946-0362 C4, C5: X7R OR COG/NPO D1: MOTOROLA 100V, 1A, SMD SCHOTTKY (800) 441-2447 L1: COILCRAFT DO3316P-224 (847) 936-6400 6 3 L1, 220H 7 + D1 MBRS1100 FB 8 VC SYNC GND 4 R3 22k 5% C3 2200pF X7R C2 100F 10V C4 100pF 80 R1 36.5k 1% 70 VOUT 5V 0mA TO 500mA EFFICIENCY (%) + FOR 3.3V VOUT VERSION: R1: 24.3K, R2: 14.7k L1: 150H, DO3316P-154 IOUT: 0mA TO 500mA The LTC1627 is a synchronous stepdown switching regulator that is optimized for Li-Ion batteries in low voltage applications such as cellular phones and PDAs. This low dropout regulator combines constant frequency current mode control, Burst Mode operation and built-in power switches in an SO-8 package to offer the most compact and efficient power management solution for portable applications operating from 1- or 2-cell lithium-ion batteries. 50 40 R2 12.1k 1% VIN = 12V VIN = 24V 30 VIN = 36V VIN = 48V 20 1 1676 F04a 10 100 ILOAD (mA) 1000 1676 F04b Figure 2. Efficiency of Figure 1's Circuit Figure 1. Minimum Component Count Application High Efficiency 500mA Step-Down Switcher Operates from 1- or 2-Cell Li-Ion Batteries 60 A 2.5V output supply powered from a single Li-Ion battery (3.5V to 4V) can be constructed with the LTC1627 with few external components. Output voltage is userprogrammable and can be set as low as 0.8V. Switching frequency of 350kHz allows the use of small surface mount inductors and capacitors. Efficiencies in excess of 90% over a wide range of output current and 100% duty cycle allow the user to extract the maximum power available from the battery. A precision 2.5V undervoltage lockout prevents battery damage due to overdischarge by shutting the LTC1627 down, drawing only 5A of supply current. A secondary feedback pin allows regulation of the secondary winding output even when the main output is lightly loaded by forcing continuous operation. The LTC1627 is an ideal choice for battery-powered applications including Li-Ion, NiCd and NiMH up to 8.5V where you need a step-down regulator with excellent efficiency in a very small footprint. Efficiency vs Output Load Current 100 95 EFFICIENCY (%) VIN 12V TO 48V 90 85 80 75 70 VIN = 5V VOUT = 3.3V 10 100 OUTPUT CURRENT (mA) 1000 1627 F01b Contact your local Linear Technology sales office for a data sheet and evaluation samples. For more information, visit our web site at www.linear-tech.com. 2 Linear Technology Chronicle * December 1998 LTC1650: 16-Bit Voltage Output DAC Now Available for 5V Supply Systems The LTC1650 from Linear Technology delivers true 16-bit monotonic performance while dissipating only 75mW from 5V supplies. The buffered voltage output swings rail-to-rail into 1000pF. The bipolar or unipolar output is selected by pin connections. The LTC1650 also features fast settling time of 4s to 16 bits and a low 2nV-s midscale glitch for applications where dynamic performance is required. A user-defined reset voltage is used to determine the output of the DAC during power-up or when a clear command is issued. The LTC1650 also contains a power supply sense circuit that activates the reset and notifies the system when any of the three supplies goes away. The reference input determines the full-scale output and has a range of - 4.0V to 4.5V allowing 4-quadrant multiplication. The serial interface simplifies isolated applications and is cascadable allowing multiple DACs to be connected on the same data I/O line. It is contained in a narrow 16-pin package for minimal board space consumption. 5V 5V 3 DVDD 11 RSTOUT REFHI 1.0 15 10 AVDD 0.8 8 CLK 7 DIN 5 0.6 POWER-ON RESET SUPPLY SENSE 9 CLR 2 VRST DNL ERROR (LSB) CS/LD 4.096V 16-BIT DAC 16-BIT DAC REGISTER 16-BIT SHIFT REGISTER DOUT + 1 VOUT - 6 0.4 0.2 0 - 0.2 - 0.4 - 0.6 - 0.8 16 4 DGND 12,13 14 REFLO AVSS UNI/BIP - 1.0 0 16384 32768 CODE 49152 65535 1650 TA01 1650 TA02 - 5V Figure 2. Differential Nonlinearity vs Input Code Figure 1. Voltage Output DAC Is 16-Bit Monotonic Over Temperature LT1786F: SMBus Programmable Backlight Supply The LT1786F is a fixed frequency, current mode switching regulator designed for SMBus control of CCFL (Cold Cathode Fluorescent Lighting) displays. A wide input range of 4.5V to 30V allows the circuit to operate well from 5V supplies, from high voltage wall adaptors and from widely varying battery inputs. The 2-wire SMBus serial interface of the LT1786F provides simple "bits-tolamp-current" output control. The circuit contains a high current switch, an oscillator, 90% Efficient Floating CCFL with 2-Wire SMBus Control of Lamp Current D1 BAT85 LAMP 10 1 2 3 ICCFL CCFL VSW BULB 16 DIO 5 12 7 8 AGND VCC SHDN IOUT SMBSUS SCL ADR SDA L1 3 11 R2 220k + 3V VCC 6.5V C4 2.2F 1 4 5 C3B 2.2F 35V + R1 750 C1* 0.068F R3 100k 10 9 2 + 14 BAT LT1786F 13 CCFL VC ROYER 6 C5 1000pF 15 4 C7, 1F SHUTDOWN CCFL PGND C2 27pF 3kV 6 Q2* TO SMBus HOST SEE DATA SHEET FOR COMPONENT INFORMATION CCFL BACKLIGHT APPLICATION CIRCUITS CONTAINED IN THE LT1786F DATA SHEET ARE COVERED BY U.S. PATENT NUMBER 5408162 AND OTHER PATENTS PENDING Q1* L2 100H D1 1N5818 1786F TA01 BAT 8V TO 28V C3A 2.2F 35V output drive logic, control circuitry and a micropower 6-bit DAC. The precision, 100A output, full-scale DAC assumes midrange or zero scale on power-up depending upon the SMBus address selected. The LT1786F acts as an SMBus slave device using one of two selectable addresses. The circuit operates with either grounded lamp or floating lamp configurations. No sense resistor is required for floating lamp operation and no external diodes are required for grounded lamp operation. The LT1786F offers two shutdown modes. When shut down by an SMBus command, digital data for the DAC output current is retained internally and the supply current drops to 40A for standby operation. A second shutdown function disables the CCFL control circuitry but keeps the DAC alert and draws 150A supply current. The LT1786F has a switching frequency of 200kHz for small component sizes. The circuit is available in a 16-pin narrow SO package. Contact your local Linear Technology sales office for a data sheet and evaluation samples. For more information, visit our web site at www.linear-tech.com. Linear Technology Chronicle * December 1998 3 LTC1694: SMBus Accelerator Improves Data Integrity lower pull-up resistor values, but the additional current through the low value resistors increases the low state bus voltage, decreasing noise margins. Slow rise times can Compensates for Bus Loading 1s RISE LTC1694 SPEC The LTC1694 is a dual SMBus active pull-up designed to enhance data transmission speed and reliability under all specified SMBus loading conditions. With the LTC1694, the user can connect more devices or use longer, more capacitive interconnects without compromising slew rates or penalizing bus performance. Resistive pull-ups are used in many communications protocols that employ opencollector or open-drain devices. Their simplicity is offset by the relatively slow rise times they afford when bus capacitance is high. Rise times can be improved by using 14.3k RESISTOR VIOLATION TIME PICC 4V VIHmin (80% VCC) I2C SCHMITT TRIGGER INPUT SMBus STD 1.4V VIHmin ~ 3s SKEW GND VERT: 1V/DIV HORIZ: 1s/DIV Test Conditions: Linear Technology DC134C Demo Board (5.0V SMBus Supply, PIC16LC73A C, Smart Battery) Figure 1. SMBus Open-Drain Signal Rise Times seriously affect data reliability, lowering practical bus speed and violating SMBus standards. The LTC1694 overcomes these limitations by using bilevel, hysteretic current sources as pull-ups. During positive bus transition, the current sources provide 2.2mA to quickly slew the SMBus line despite any parasitic bus capacitance (Figure 1). During negative transitions or steady DC levels, the current sources switch to 275A, within the SMBus limit of 350A, to improve negative slew rate and improve low state noise margins. An autodetect standby mode reduces supply current if the bus is idle. The LTC1694 is available in the 5-lead SOT-23 plastic surface mount package, requiring virtually the same board area as two surface mount resistors. LTC1597: Ultra-Accurate 16-Bit DAC with On-Chip 4-Quadrant Resistors impulse to less than 2nV-s typically. The LTC1597 has an asynchronous clear input that resets the output to zero scale. A second version, the LTC1597-1, resets to midscale. The circuit has power-on reset and is double-buffered with two 16-bit registers, a feature that permits the update of several DACs simultaneously. The parallel input of the LTC1597 is advantageous for fast settling applications. Used with the LT1468 high speed op amp, the circuit's settling time to 0.0015% with a 10V step is 2s. See Application Note 74. The LTC1597 is designed for applications such as process control and industrial automation, direct digital waveform generation, software-controlled gain adjustment and automatic test equipment. The LTC1597 operates with very low supply power dissipation, typically 10W. The circuit is available in a 28-pin SSOP package and is specified over the commercial and industrial temperature ranges. Contact your local Linear Technology sales offfice for a data sheet and evaluation samples. For more information, visit our web site at www.linear-tech.com. LTC1597/LTC1597-1 Integral Nonlinearity 1.0 VREF = 10V VOUT = 10V BIPOLAR 0.8 INTEGRAL NONLINEARITY (LSB) The LTC1597 is a parallel input 16-bit multiplying current output DAC that operates from a single 5V supply. INL and DNL are accurate to 1LSB over the industrial temperature range in both 2- and 4-quadrant multiplying modes. True 16-bit, 4-quadrant multiplication is achieved with on-chip precision resistors. The sensitivity of INL and DNL to op amp offset has been greatly reduced compared to previous generations of multiplying DACs. For the LTC1597, a 500V op amp offset will cause about 0.55LSB INL degradation and 0.15LSB DNL degradation with a 10V full-scale range. The DAC unipolar output range is 0V to -10V and the DAC bipolar output range is 10V for a fixed 10V reference input. The device includes an internal deglitcher circuit that reduces the glitch 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 0 49152 32768 16384 DIGITAL INPUT CODE 65536 1597 TA02 16-Bit, 4-Quadrant Multiplying DAC VREF + 3 R1 2 RCOM R1 LTC1597-1 10 TO 21, 24 TO 27 5 23 4 VCC ROFS ROFS RFB RFB 16-BIT DAC 33pF IOUT1 - 6 AGND DGND 7 +LT1468 VOUT = -VREF TO VREF 22 1597 TA01 WR LD CLR WR LD CLR 1 REF R2 16 DATA INPUTS Linear Technology Products Are Distributed By: 5V 0.1F -LT1468 9 8 28 Arrow Electronics Digi-Key Electrosonic Gerber Electronics Marshall Industries Phase 1 (c) 1998 Linear Technology Corporation/Printed in USA 4 Technology Corporation * 1630 McCarthy Blvd. * Milpitas, CA 95035-7417 * (408) 432-1900 * FAX: (408) 434-0507 Linear * www.linear-tech.com * For Literature 1-800-4-LINEAR Linear Technology Chronicle * Only: December 1998