LinearTechnologyChronicle A Showcase of Linear Technology's Focus Products November 1996 Products of the Month Software-Selectable Multiprotocol Chip Set Simplifies Data Networking Interface Design The LTC(R)1343 multiprotocol transceiver and companion LTC1344 cable terminator form a complete software-selectable multiprotocol serial port, operating from a single 5V supply. This is the first integrated solution to pass the stringent NET1 and NET2 tests of the European Telecommunications Institute. The LTC1343 contains four drivers and four receivers and the configuration logic to do protocol selection, loopback testing as well LATCH as turning on and off the echo clock and the low power shutdown mode. The LTC1343/ LTC1344 can be used in both DTE and DCE equipment. The LTC1344 cable terminator contains six switchable resistive terminations to configure a single DB-25 connector for up to eight different serial protocols. Two LTC1343 transceivers and a single LTC1344 terminator form a DTE or DCE interface port, capable of supporting RS232 (V.28), RS423 (V.10), EIA530, EIA530-A, RS449, V.35, 21 LTC1344 DCE/ DTE M2 22 23 M1 M0 (DATA) 24 1 CONNECTOR (DATA) R1, 10k LTC1343 M0 17 R2, 10k 20 M1 CTRL/CLK 18 R3, 10k 22 M2 LATCH 19 21 VCC VCC NC R4, 10k DCE/DTE VCC VCC NC CABLE LTC1343 DCE/DTE M2 VCC 20 22 CTRL/CLK M1 LATCH M0 21 19 18 17 (DATA) V.36 and X.21 protocols that are both NET1 and NET2 compliant. This chip set is ideal for space limited networking applications and supports all major telecom protocols for remote access serial ports. In a typical application, the first LTC1343 is connected to the clock and data signal lines along with the diagnostic LL (local loop-back) and TM (test mode) signals. The second LTC1343 is connected to the control signal lines along with the diagnostic RL (remote loop-back) signals. Switching between modes is simple--just three mode select pins are required for both the LTC1343 and LTC1344, as shown in Figure 1. The mode pins are latched internally to allow sharing of the select lines between multiple interface ports. DTE or DCE is set with one pin, as is the designation for whether the transceiver is used for data and clock signals or control signals. This greatly simplifies the task of switching eight different types of serial ports to the same DB-25 connector, as shown in Figure 2. Other routing tasks, such as loopback testing or echo clocking, are also easily performed. The LTC1343 is packaged in a 44-lead SSOP and the LTC1344 in a 28-lead SSOP. Together they eliminate the switches, relays and jumpers normally required to switch between drivers, receivers and associated termination schemes. The three chips together occupy only 8 cm2 of board area, ideal for space constrained applications. For a data sheet and evaluation samples of this multiprotocol chip set, contact your local Linear Technology sales office. MODE SELECT 3 LTC1344 2 CLK AND DATA 4 LTC1343 3 CLK AND DATA 6 5 Figure 1. The LTC1343 and LTC1344 Address the Problem of Easily Switching the Terminations for Different Protocols Using a Single Connector. Here it is Configured for Single Port DCE and V.35 CONTROL LTC1343 CONTROL 13 12 11 10 Controller IC Allows Safe Hot Swapping of Circuit Boards ..................................................... 2 First Dual 12-Bit Voltage Output DAC in SO-8 Runs on 3V Supply ........................................ 2 Micropower Dual JFET Op Amps Feature pA Input Bias Currents and C-LoadTM Drive Capability ........................................................................................................ 3 9 8 7 Inside This Issue: 25 24 23 22 21 20 19 18 17 16 15 14 1 1343 F11 Vol. 5 No. 11 RS232 EIA-530 EIA-530-A RS449 V.35 V.36 X.21 Find Linear Technology's Products on CD-ROM--Fast and Free ! ......................................... 4 Dual DAC Adds Features to Single 5V Supply, 12-Bit Family ................................................. 4 , LTC and LT are registered trademarks of Linear Technology Corporation. C-Load is a trademark of Linear Technology Corporation. Linear Technology Chronicle * November 1996 DB-25 Figure 2. Single 5V Complete Multiprotocol Serial Port 1 Controller IC Allows Safe Hot Swapping of Circuit Boards The LTC1421 hot swap controller safely limits the inrush currents that can destroy components and traces on circuit boards and prevents glitches that disrupt the system bus when a circuit board is plugged into a live backplane. The device can turn on up to three board supply voltages at programmable rates. The LTC1421 is ideal for backplanes and rack systems that must run continuously or cannot tolerate glitches on the supply rails when inserting or removing circuit boards. It is appropriate for power systems supplying 3V/5V, 5V/12V or even - 48V/5V telecom voltages. The key to controlling the inrush current is the user-programmable power-up rate. An external capacitor sets the timing for the ramp-up of the positive FET voltages resulting in the switches being turned on slowly and the current being held to an acceptable level. A sense resistor in series with the FETs, shown in Figure 1, is used to detect excessive current levels. Both positive FETs are ramped up at the same rate, with the higher voltage FET kept above the lower voltage FET to prevent power sequencing problems. The chip includes undervoltage lockout and a voltage comparator to generate a reset signal. Voltage levels can be monitored using the uncommitted comparator and the 1.232V reference. Power management functions include data bus disable, reset input, system reset and power good signals. During board insertion or removal, the disable signal can be used to halt the system bus by putting the bus buffer in a high impedance state. The reset input allows recycling the power with a pushbutton or external signal. The reset output and power good output signals are used by the processor for general power management functions. The LTC1421 controller provides warning signals when power fails, the circuit breaker has tripped or when the switches have been turned off. Separate controls are available for power-on reset or disabling the data lines. The LTC1421 is available in the 24-pin SO and SSOP packages. For a data sheet and evaluation samples, contact your local Linear Technology sales office. Q3 1/2 Si4936DY C3 0.47F VEE R4 20k 5% Q2 R2 0.025 1/2 Si4936DY + VDD + R1 0.005 STAGGERED CONNECTOR 23 D1 22 21 20 19 VCCLO SETLO GATELO VOUTLO VCCHI R3 1k 2 CON2 24 AUXVCC C1 1F 4 FAULT LTC1421 FAULT 3 POR 1 CON1 POR GND 12 GND DATA BUS 18 DISABLE 5 C2 0.1F 16 RAMP CPON COMP - COMP + REF FB COMPOUT PWRGD RESET 10 9 14 13 8 11 15 6 7 1 BEA VCC 13 BEB 12 GND QS3384 QuickSwitch(R) BACKPLANE 17 SETHI GATEHI VOUTHI R5 16k 5% R6 20k 1% VDD 12V 1A C3 220F Q1 MTB50N06E VCC VEE - 12V 1A C5 220F + C4 220F VCC 5V 5A R7 7.15k 1% P I/O I/O RESET DATA BUS 1421 TA01 QuickSwitch IS A REGISTERED TRADEMARK OF QUALITY SEMICONDUCTOR CORPORATION. PC BOARD Figure 1. The LTC1421 Can Drive Three N-Channel MOSFETs That Switch the Power from the Backplane to the Circuit Board. Resistors in Series with the Power FETs Sense Excessive Current Levels First Dual 12-Bit Voltage Output DAC in SO-8 Runs on 3V Supply The LTC1446L is a dual 12-bit voltage output digital-to-analog converter that is complete with two rail-to-rail voltage output amplifiers, a 1.22V bandgap voltage reference and a 3-wire cascadable serial interface, all packed into an 8-pin SO package. The 2 maximum differential nonlinearity (DNL) is only 0.5LSB. It consumes just 2mW from a single 3V supply making it the best solution for portable and battery-powered equipment. Better than 12-bit monotonicity over temperature makes the LTC1446L ideal for feedback control applications such as industrial control loops and general purpose trim pots. The 2.5V output voltage is guaranteed even with a reduced supply of 2.7V. The DAC outputs drive capacitive loads of up to 1000pF. Power-on reset insures the DACs start in a known state after power up, easing initial processor overhead. Figure 1 shows a typical application for the LTC1446L. The excellent typical differential nonlinearity (DNL) of 0.2LSB (Figure 2) not only guarantees 12-bit monotonic performance but also provides exceptional performance in closed loop control systems. The LTC1446L's 3-wire serial interface allows several dual DACs to be daisyContinued on page 3 Linear Technology Chronicle * November 1996 Application of the Month Micropower Dual JFET Op Amps Feature pA Input Bias Currents and C-Load Drive Capability The LT(R)1462/LT1463 low input bias currents make them a natural for amplifying low level signals from high impedance transducers. The 1pA input bias current contributes only 0.4fA/Hz of current noise or 0.4nV/Hz voltage noise with a 1M source impedance. A 1M impedance's thermal noise of 130nV/Hz dominates the op amp's noise, showing that even with high source impedances, the LT1462/LT1463 contribute very little to total input-referred noise. Taking advantage of these features, Figure 1's R8 100k photodiode logging amplifier uses two LT1462 duals or an LT1463 quad. Here, the photodiode current is converted to a voltage by the first op amp and D1 and amplified by the first, second and third logarithmic compression amplifiers. A DC feedback path comprising R8, R9, C6 and Q1 is active only for no-light conditions. Q1 is off when light is present, isolating the photodiode from C6. When feedback is needed, a small filtered current through R8 prevents the op amp outputs from saturating when no signal is present as shown in Figure 2. The LT1462/LT1463 family is especially suited for piezo transducer conditioning, strain gauge weight scales, very low droop track-and-holds, wide dynamic range photodiode amplifiers and other applications that benefit from pA input bias current. The family also exhibits very low noise current, important to circuits such as low frequency filters. These op amps allow high value resistors to be used with easily obtainable, low value precision capacitors to set a filter's frequency characteristics without compromising noise performance. Q1 2N3904 D1 1N4148 C6 1F R9 1M - 1.6 PHOTODIODE 5V 2 3 - 8 AMP 1 1/2 LT1462 C1 1nF 1 + - 1.4 R2 24k 5 C2 200pF 4 6 -5V + - R5 24k 7 AMP 2 1/2 LT1462 R4 10M C5 200pF 3 2 AMP 3 1/2 LT1462 D2 1N4148 5V R7 10M D3 1N4148 R3 100k C3 DC 0.47F OUT 1 + - AMP 3 DC OUTPUT (V) R1 100 R10 50k 5 6 + AMP 4 1/2 LT1462 - R6 100k C4 10F 8 AC OUT 7 - 5V R11 1M R12 10k - 0.8 - 0.6 - 0.4 - 0.2 R13 10k 4 - 1.2 - 1.0 0 10 -11 The LTC1446L is available in 8-lead SO and PDIP packages screened to the commercial and industrial temperature ranges. chained to save board space and is compatible with SPI, QSPI and MICROWIRETM protocols. 7 10 -3 DN136 F03 Figure 2. Logging Photodiode Amplifier DC Output Figure 1. This Logging Photodiode Amplifier Takes Advantage of the LT1462's 1pA Input Bias Current to Amplify the Low Level Signal from the Photodiode's High Source Impedance LTC1446L from page 2 10 -9 10 -7 10 -5 PHOTODIODE CURRENT (A) DN136 F02 Contact your local Linear Technology sales office for a data sheet and evaluation samples. MICROWIRE is a trademark of National Semiconductor Corp. LTC1446L: 3V TO 5V LTC1446L: 1.22V 2 DIN + 0.5 8 12-BIT DAC B - 0.3 1 CLK 3 CS/LD 24-BIT SHIFT REG AND DAC LATCH RAIL-TO-RAIL VOLTAGE OUTPUT + 5 12-BIT DAC A VOUT A - DNL ERROR (LSB) P 0.4 VOUT B 0.2 0.1 0 -0.1 -0.2 -0.3 -0.4 4 DOUT -0.5 0 POWER-ON RESET 512 1024 1536 2048 2560 3072 3584 4095 CODE 1446/46L G12 6 1446/1446L TA01 Figure 1. The LTC1446L Dual 12-Bit DAC is the First in an 8-Pin SO Package to Operate with a Single 3V Supply Linear Technology Chronicle * November 1996 Figure 2. Typical Differential Nonlinearity vs Input Code for LTC1446L is Only 0.2LSB. Maximum DNL is 0.5LSB 3 Find Linear Technology's Products on CD-ROM-- Fast and Free! SwitcherCADTM and FilterCAD. It contains all LTC product data sheets including those that have appeared in the 1990, 1992, 1994 and 1995 databooks and Design Notes. Also included are all issues of Linear Technology magazine. Familiar WindowsTM appearance and appealing organization of topics facilitate easy use by the PC user. Try this new powerful tool and explore what it can offer. A free copy of the LinearView CD-ROM is yours for the asking. Contact your local Linear Technology sales office. LinearViewTM is the easiest and quickest way of navigating over 8000 pages of data sheets, Application Notes and Design Notes in search of a particular topic or part number. Powerful search engines are employed for "key word" or "by parameter" searching to select the best product for a particular application. LinearView is also handy for design analysis, and includes LTC's popular design software programs, such as LinearView and SwitcherCAD are trademarks of Linear Technology Corporation. Windows is a trademark of Microsoft Corporation. Dual DAC Adds Features to Single 5V Supply, 12-Bit Family choice for portable or battery-powered equipment. The LTC1454 contains two 12-bit DACs with rail-to-rail output amplifiers, a 3-wire, cascadable serial interface and a 2.048V bandgap voltage reference. Offset error is only 18mV (max). The LTC1454 has an asynchronous Clear pin which resets all DACs to zero scale. A unity/2X gain select pin lets the user set the gain of the output amplifiers. The on-chip reference is available for external circuitry and is not internally connected, allowing a user specified reference input. The LTC1454 is a dual 12-bit DAC that consumes 3.5mW (typ) from a single 5V supply and has a differential nonlinearity (DNL) of only 0.5LSB. This makes it ideal for feedback control applications such as industrial control loops and general trim pots. The low power consumption and high integration make the LTC1454 an excellent LTC1454: 5V LTC1454L: 3V TO 5V 9, 15 VCC LTC1454: 2.048V 10 LTC1454L: 1.22V REFOUT REFHI B 14 + 4 DIN P 3 CLK 5 CS/LD 6 DOUT VOUT B 16 - 12-BIT DAC B 24-BIT SHIFT REG AND DAC LATCH X1/X2 B 1 + 12-BIT DAC A REFLO CLR 12 REFHI A 11 VOUT A 8 X1/X2 A 7 - POWER-ON RESET 2 The rail-to-rail amplifiers have improved capacitive load handling over competing devices and swing to 4.095V full scale even when running on a 4.5V supply. The serial I/O is cascadable which reduces interface hardware when multiple DACs are used. Power-on reset insures the DACs start in a known state after power up and Clear resets the DAC to zero scale asynchronously. For a data sheet and evaluation samples of this high performance ADC, contact your local Linear Technology sales office. Linear Technology Products Are Distributed By: GND 13 1454 BD02 Figure 1. LTC1454 Dual 12-Bit Rail-to-Rail DAC Offers Many Features in Its 16-pin SO Package. 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 November 1996