What’s New with LTspice IV? Gabino Alonso Stepping Parameters in LTspice IV NEW HOW-TO VIDEOS Stepping Parameters video.linear.com/103 There are two ways to examine a circuit by changing the value of a parameter. You can manually enter each value, then resimulate the circuit, or you can use the .STEP command to sweep across a range of values in a single simulation run for a side-by-side comparison. This video provides an overview of the basic steps for using the .STEP command to perform repeated analysis of a circuit. FULLY DIFFERENTIAL OPERATIONAL AMPLIFIER DEMO CIRCUITS (from Tyler Hutchison) Analyzing and interfacing with fully differential op amps in simulation may prove more complicated than with familiar, single-ended output op amps. These demo circuits provide examples of interfacing to fully differential amplifiers What is LTspice IV? LTspice® IV is a high performance SPICE simulator, schematic capture and waveform viewer designed to speed the process of power supply design. LTspice IV adds enhancements and models to SPICE, significantly reducing simulation time compared to typical SPICE simulators, allowing one to view waveforms for most switching regulators in minutes compared to hours for other SPICE simulators. LTspice IV is available free from Linear Technology at www.linear.com/LTspice. Included in the download is a complete working version of LTspice IV, macro models for Linear Technology’s power products, over 200 op amp models, as well as models for resistors, transistors and MOSFETs. 32 | April 2012 : LT Journal of Analog Innovation Follow @LTspice on Twitter for up-to-date information on models, demo circuits, events and user tips: www.twitter.com/LTspice including single-ended and differential impedance matching, noise analyses, mixer and high speed ADC signal chain models, and gain modification of fixedgain amplifiers with external resistors. • LTC6405: Fully differential ADC driver with simplified mixer and ADC models www.linear.com/LTC6405 • LTC6400-20: Single-ended impedance matching for fully differential amplifiers www.linear.com/LTC6400-20 • LTM®8048: Isolated µModule DC/DC converter with LDO post regulator (4V–30V to 6V at 100m A & 5V at 100m A) www.linear.com/LTM8048 • LTC6400-20: Differential impedance matching for fully differential amplifiers www.linear.com/LTC6400-20 • LTC6400-20: Noise simulation for fully differential amplifiers www.linear.com/LTC6400-20 • LTC6401-8: Unity gain for fully differential amplifiers with internal feedback resistors www.linear.com/LTC6401-8 • LTC6404-1: Impedance matching and noise measurements for fully differential amplifiers www.linear.com/LTC6404 NEW DEMO CIRCUITS µModule Regulators • LTM8052: 36V, 5A, 2-quadrant CVCC stepdown µModule regulator (6V–36V to 2.5V at ±5A) www.linear.com/LTM8052 Switching Regulators • LT3758: High efficiency SEPIC (8V–72V to 5V at 2A) www.linear.com/LT3758 • LT3759: Boost with low input voltage range (1.8V–4.5V to 5V at 2A) www.linear.com/LT3759 • LT3759: SEPIC with wide input voltage range (2.8V–36V to 12V at 1A) www.linear.com/LT3759 Download this demo circuit showing impedance matching and noise measurements for fully differential amplifiers www.linear.com/LTC6404 design ideas • LTC4000/LTC3891: High voltage high current step-down, PowerPath controller & Li-ion battery charger (24V–60V to 16.8V at 6A) www.linear.com/LTC4000 Amplifiers, References, Comparators and TimerBlox ® IC s • LT6108/LTC6994: Energy-tripped circuit breaker with automatic delayed retry (5V–80V input, 500m A threshold) www.linear.com/LT6108 PARAMETRIC PLOTS Plotting results in LTspice IV is as easy as clicking on a node to show voltage, or a component to show current—the trace is then displayed in the waveform viewer. In transient analysis, the horizontal axis defaults to showing time, but you can always change the horizontal axis to show other quantities (such as current) to validate model parameters. To change the default settings of the x-axis: 1.Click on a node/component to plot its voltage/ current in the waveform viewer. 2.Move the cursor to the horizontal axis of the waveform viewer (the cursor will turn into a ruler) and left-click. 3.In the Horizontal Axis dialog, enter an expression for the “Quantity Plotted.” 4.Click OK. Happy simulations! NEW DEVICE MACRO MODELS Switching Regulators • LT8582: Dual 3A boost/inverting/ SEPIC DC/DC converter with fault protection www.linear.com/LT8582 • LTC3103: 1.8µ A quiescent current, 15V, 300m A synchronous step-down DC/DC converter www.linear.com/LTC3103 • LTC3115V–1: 40V, 2A synchronous buck-boost DC/DC converter www.linear.com/LTC3115-1 • LTC3613: 24V, 15A monolithic step-down regulator with differential output sensing www.linear.com/LTC3613 • LTC3839: Fast, accurate, 2-phase, single-output step-down DC/DC controller with differential output sensing www.linear.com/LTC3839 • LTC3866: Current mode synchronous controller for sub-mΩ DCR sensing www.linear.com/LTC3866 • LTC3876: Dual DC/DC controller for DDR power with differential VDDQ sensing and ±50m A VTT reference http://www.linear.com/LTC3876 This parametric plot compares the instantaneous power dissipation (Alt + click on component) of an LTC4358 5A ideal diode to a Schottky diode. In this example, the quantity plotted on the horizontal axis has been changed from the default of “time” to “load current.” The resulting plot confirms the advantage of the LTC4358 as a low loss replacement to Schottky diodes in high current diode applications. More information is available at www.linear.com/LTC4358. • LTC4366: High voltage surge stopper www.linear.com/LTC4366 n LTC4358-BASED, LOW LOSS, IDEAL DIODE SOLUTION Power User Tip Download the LTspice IV demonstration circuit for this energy-tripped circuit breaker with automatic delayed retry at www.linear.com/LT6108 R3 3.66k LOAD SUPPLY 5V TO 80V DC R4 0.667V/A 40.2k LT6108-2 CURRENT SENSE AMP R1 100Ω RSENSE 10mΩ – + 5V + 60ms TO 350ms DELAY TIMER LT1783 IN R6 64.9k R3 6.34k 400mV – + LRELAY Q1 NPN R2 1.62k 5V – COMPARATOR CIRCUIT BREAKER Hot Swap™ Controllers and Surge Stoppers • LTC4232: 5A integrated Hot Swap controller www.linear.com/LTC4232 SCHOTTKY DIODE (B530C) R14 15k 5 0 CURRENT SENSE COMPARATOR 500mA TRIP THRESHOLD OUT LTC6994-2 GND SET 5V R7 301k R10 10k ROPTIONAL 931k V+ 5V DIV R8 172k R9 100k CLOSED OPEN LOAD April 2012 : LT Journal of Analog Innovation | 33