LinearTechnologyChronicle A Showcase of Linear Technology's Focus Products September 1996 Products of the Month Micropower 8-Channel 12-Bit ADCs with MUX Offer 0.75LSB Max DNL The LTC(R)1598/LTC1598L are 8-channel multiplexed 12-bit micropower ADCs for single 5V and 3V supply applications. The 5V LTC1598 typically draws just 320A at 16.8ksps sampling rates while the 3V LTC1598L draws only 250A at 10.5ksps. Both save power by automatically powering down to a mere 1nA when not converting. Each has an 8-channel high impedance input and are packaged in a 24-pin SSOP. Maximum differential linearity error of 0.75LSB guarantees a true 12-bit no-missing codes resolution. They are ideal for such space conscious, power sensitive applications as pen screen interface, remote process control, battery monitoring and portable data acquisition. These ADCs have a multiplexer output that is separate from the ADC input, allow- ing one signal conditioning circuit for all channels. This improves channel matching characteristics and reduces component count. For example, a filter can be implemented once and used for all four channels. Separate control of the multiplexer and ADC allows continuous sampling of a single channel without addressing prior to each conversion. The 3-wire serial interface reduces I/O lines in remote or isolated applications. All devices are SPI, QSPI and MICROWIRETM compatible. The LTC1598/LTC1598L are screened to the commercial and industrial temperature ranges. Contact your local Linear Technology sales office for data sheets and evaluation samples. MICROWIRE is a trademark of National Semiconductor Corp. OPTIONAL ADC FILTER 1k 5V 1F 18 MUXOUT 17 ADCIN 16 15, 19 VREF VCC 1F 20 CH0 21 CH1 CS ADC 22 CH2 ANALOG INPUTS 0V TO 5V RANGE 23 CH3 24 CH4 CS MUX 8-CHANNEL MUX + 1 CH5 12-BIT SAMPLING ADC - 2 CH6 CLK DIN DOUT 3 CH7 NC 8 COM GND 4, 9 NC 10 6 SERIAL DATA LINK MICROWIRE AND SPI COMPATABLE 5, 14 7 MPU 11 12 13 LTC1598 * TA01 Figure 1. LTC1598 24W, 8-Channel, 12-Bit ADC Samples at 200Hz and Runs Off a 5V Supply Inside This Issue: Vol. 5 No. 9 Adaptive Frequency Boost Converters Provide Low Noise and High Efficiency Over a Wide Range of Loads The LT(R)1500/LT1501 are low noise micropower DC/DC converters for battery applications using two or more cells or a supplied voltage of 1.8V minimum. The current mode architecture monitors the switch current to produce a well controlled peak switch and battery current. These high efficiency converters provide low noise 5V to 12V conversion at 200mA or can deliver 300mA at 3.3V from just two cells (2V minimum). Operating quiescent current is just 200A and only 8A (typ) in shutdown. They are capable of operating with supply voltages from 1.8V to 15V. The LT1500/ LT1501 are ideal for communications applications, such as wireless modems, which require good efficiency and fairly constant frequency operation with low switching noise over a wide range of load currents. The LT1500 requires only four external surface mount components to implement a current mode boost converter--input and output capacitors, an inductor and a diode. The switching frequency is determined by the input and output voltages and inductor value, so it will vary somewhat as the input voltage changes. In contrast to pulse skipping switching regulators, the current mode operation of the LT1500/LT1501 causes the operating frequency to linearly increase as the load current decreases. This keeps the switching frequency out of the audio band at most load currents. The LT1500 has an advantage over other variable frequency methods which can cause the switching frequency to vary into the audio range. Continued on page 2 TM World's Only Dual, Micropower, C-Load JFET Op Amps .................................................... 2 Driving the Analog Input of High Performance A/D Converters .............................................. 3 New Data Conversion Solutions Brochure ............................................................................. 4 SwitcherCADTM Update ............................................................................................................ 4 , LTC and LT are registered trademarks of Linear Technology Corporation. C-Load and SwitcherCAD are trademarks of Linear Technology Corporation. Linear Technology Chronicle * September 1996 1 22H LT1500/LT1501 from page 1 5V, 200mA The LT1500 is offered in a 14-lead SO package with two options available for fixed output (3.3V or 5V) or adjustable operation and includes a synchronization function. The LT1501 is in an 8-lead SO package and is not synchronizable. Both devices include a low-battery detector which is alive in shutdown. Contact your local Linear Technology sales office for a data sheet and evaluation samples. IN 301k 1% 2 EACH NiCd OR ALKALINE CELLS + ISENSE SHDN 33F* 6V SW + 220F** 10V TANT LT1501-5 LBI 301k 1% OUT LBO * AVX, TPSC107M006R0150 ** AVX, TPSD107M010 R0100 SUMIDA CD73-220, CD54-220 OR CD43-220. SELECT ACCORDING TO MAXIMUM LOAD CURRENT GND 1nF LOW-BATTERY FLAG (USE EXTERNAL PULL-UP) LT1500/01 * TA01 Figure 1. LT1501 Used as a 2-Cell to 5V Converter World's Only Dual, Micropower, C-Load, JFET Op Amps power savings--extending battery life and maintaining low bias currents by running cooler than other JFETs. They are ideally suited for battery-powered systems, photo current amplifiers and as low frequency, micropower active filters. The LT1462 and LT1464 are micropower op amps that draw only 45A and 200A max respectively, yet they are still capable of driving large capacitive loads. Both of these C-Load stable op amps require just picoamperes of input bias current (0.5pA typical) and are unity-gain stable The LT1462 and LT1464 are dual JFET input amplifiers that consume only 45A and 200A of supply current per amplifier, respectively. The LT1462 has a slew rate of 0.13V/s and 175kHz bandwidth. The LT1464 has a slew rate of 0.9V/s and 1MHz bandwidth. These low power JFET amplifiers offer tremendous for capacitive loads up to 10,000pF. Their outputs can swing a 10k load to within 1.5V of either supply while their input common mode range can swing to and include the positive rail. The LT1462 and the LT1464 are offered in standard 8-pin DIP and SO packages. The quad versions, LT1463 and LT1465, will soon join this family of micropower JFET amplifiers. Contact your local Linear Technology sales office for data sheets and evaluation samples. V+ A 1/4 LTC201 13 15 4 14 C1 10nF POLYSTYRENE 16 1 MCT2 5 V+ V- 5 2 + 1/2 LT1464 6 IN 1/4 LTC201 B 7 4 - 1 MCT2 5 - 8 3 + 2 6 4 3 MODE Track Reset Reset IN A IN B 0 0 0 0 0 0 1 VOUT 4 V- 2 FUNCTION Track-and-Hold Positive Peak Detector Negative Peak Detector 2 1/2 LT1464 1 5 6 R1* LT1464 * TA01 0.5pA = 0.05mV/s 10nF TOTAL SUPPLY CURRENT = 460 A MAX * R1 = 600 FOR 15V SUPPLIES R1 = 0 FOR 5V SUPPLIES TYPICAL DROOP = MODE IN A IN B Hold 1 1 Store 0 1 Store 1 0 AV = 1 VS = 5V, 15V CL = 10nF 1464 TA02 Figure 2. Small-Signal Response, CLOAD = 10nF LTC201 switch is open for logic "1." Figure 1. LT1464 JFET Input Op Amp as a Micropower Low Droop Track-and-Hold/Peak Detector 2 Linear Technology Chronicle * September 1996 Application of the Month Driving the Analog Input of High Performance A/D Converters The inputs to switched capacitor ADCs are easy to drive if you allow for the fact that they draw a small input current transient at the end of each conversion. This happens when the internal sampling capacitors switch back onto the input to acquire the next sample. For accurate results, the circuitry driving the analog input must settle from this transient before the next conversion is started. There are two ways to accomplish this. One is to drive the ADC with an op amp that settles from a load transient in less than the acquisition time of the ADC. Fortunately, most op amps settle much more quickly from a load transient than from an input step, so meeting this requirement is not too difficult. The LT1363, for example, is a good choice for driving the LTC1410 input. A second solution to handling the input transient is to use an input RC filter with a capacitor much larger than the ADC input capacitance. This larger capacitor provides the charge for the sampling capacitor, which eliminates the voltage transient altogether. Figure 1 shows such a filter for the LTC1410. The 1000pF capacitor provides the input charge for the ADC's sampling capacitor. The LT1363's capacitive load driving capability makes it a good choice for use with this filter. Filter Wideband Noise from the Input Signal Many new converters have wide S/H input bandwidths. This is great for capturing high frequency input signals, but for lower input bandwidth applications the converter will pick up any wideband noise that may be in the input signal. To avoid this, use a filter at the ADC input to pass only your desired signal bandwidth. The simple filter in Figure 1 bandlimits the input signal to 3MHz and still allows clean sampling up to the Nyquist frequency (625kHz). Figure 2 shows the Nyquist performance of the LTC1410 using this filter. The signal to noise and distortion ratio (SINAD) is 71.5dB and total harmonic distortion (THD) is - 84dB. LTC1410 2.5V INPUT + 50 AIN+ LT1363 - 1000pF AIN- 20MHz S/H ADC AGND ADC_04.eps Figure 1. Many New ADCs Have Wide Bandwidth Sample-and-Holds. In Lower Bandwidth Applications, a Simple RC Filter Will Remove Wideband Noise That May Be Present in the Signal 0 fSAMPLE = 1.25Msps WITH NO JITTER fIN = 600kHz SINAD = 71.5dB -20 AMPLITUDE (dB) -40 -60 -80 -100 -120 0K 100K 200K 300K 400K INPUT FREQUENCY (Hz) 500K 600K Figure 2. With a Low Jitter Source, the LTC1410 Will Give 71.5dB SINAD When Sampling a Nyquist Input Signal Linear Technology Chronicle * September 1996 3 The 1996 Data Conversion Solutions brochure has just been published and is now available. This 52 page booklet contains practical tips on how to apply LTC's growing line of data conversion products, namely our A/D converters and DACs as well as multiplexer/switches and references. Each product section cross-references the entire product line, highlights new products for the year and then describes various applications of individual devices, complete with schematic and a description on how the circuit works. The Analog-to-Digital Converter section has tables that list the entire product line in descending sample rates, starting with the 1.25Msps LTC1410 and ending SwitcherCAD Update New software for automated power management designs now supports high frequency DC/DC converters. A new version of SwitcherCAD is now available for designing high frequency distributed power control circuits. SwitcherCAD accepts inputs for power supply requirements and returns the circuit topology, such as the external component values and the power ICs required to implement a design. Included in the component data base are new high frequency PWM switchers, such as the LT137X family, as well as new surface mount components (coils, capacitors and diodes) required for high frequency PWM operation. with low power converters under 10ksps. Other tables break out the A/D product line in terms of output (parallel or serial), micropower, 3V supply and those devices offered in the popular SO-8 package. This is then followed by several new product cameos where features of recently introduced products are presented along with a block diagram. The heart of each section is the application notes, where practical design examples are described along with a schematic. There are 60 products described and 24 application notes for you to review. Additional application notes and design notes on data conversion solutions are also referenced. The brochure concludes with a glossary of terms, including frequently used abbreviations. To receive a copy, contact your local Linear Technology sales office. The program disk runs on IBM or compatible computers and is available on a 3.5-inch floppy disk. SwitcherCAD is supplied with a 6-chapter user's manual which includes instructions on how to input data fields and what formulas to use. Vendor LINEAR TECHNOLOGY CORPORATION 1996 DATA CONVERSION SOLUTIONS First Edition Lowest Power 4-Channel 12-Bit ADC VTEMP 100W SO-8 12-Bit ADC VCC VBATT 20A CH0 CH1 GND 5V SPI, QSPI MICROWIRETM I/O SO-8 SPI, QSPI MICROWIRETM I/O SO-16 PEN SCREEN X LTC1594 SO-8 Y LTC1298 Micropower Rail-to-Rail VOUT DAC SO-8 LTC1451: 5V LTC1452: 3V TO 5V LTC1453: 3V 3-WIRE SERIAL I/O VREF Fastest 12-Bit ADC in SO-8 VCC fIN = 200kHz DIN INPUT 12-BIT SHIFT REG CS/LD AND DAC DOUT LATCH 5V -5V CLK REF OUT + RAIL-TO-RAIL VOLTAGE OUTPUT - fS = 400ksps HIGH SPEED SERIAL I/O SO-8 GND 12-BIT DAC LTC1400 POWER-ON RESET 0 fSAMPLE = 1.25MHz fIN = 599.975kHz SFDR = 84.7dB SINAD = 71.7dB -20 Best 1.25Msps 12-Bit ADC 12 fIN = 625kHz fS = 1.25Msps LTC1410 -40 AMPLITUDE (dB) New Data Conversion Solutions Brochure -60 -80 -100 -120 0 100 200 300 400 500 FREQUENCY (kHz) 600 First Edition of 1996 Data Conversion Solutions Brochure Is Now Available sources for purchasing external components are also provided. The new converter IC data base now includes the 500kHz step-down converters LT1375, LT1376, LT1507 and 250kHz to 1MHz boost converters LT1371, LT1372, LT1373 and LT1377. The original LT107X, LT117X, LT127X and LT1082 converter families are also in the data base. SwitcherCAD Version 2.18 is available free of charge from your local LTC sales representative. Linear Technology Products Are Distributed By: Almac/Arrow Arrow/Schweber Arrow/Zeus Digi-Key Electrosonic Gerber Electronics Farnell Electronics Marshall Industries Phase 1 (c) 1996 Linear Technology Corporation/Printed in USA 4 Technology Corporation * 1630 McCarthy Blvd. * Milpitas, California 95035-7417 * (408) 432-1900 *Linear Linear FAX: (408) 434-0507 * Chronicle For Literature* Only: 1-800-4-LINEAR Technology September 1996