What’s New with LTspice IV?
Gabino Alonso
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NEW HOW-TO VIDEOS
Using Transformers in
video.linear.com/93
LT spice ®
IV
Transformers and coupled inductors
are key components in many switching regulator designs, including flyback,
forward and SEPIC converters. Although
it is possible to make a dedicated subcircuit for a specific transformer, it is often
better in LTspice IV to define a separate
inductor for each transformer winding,
and then couple them all together magnetically via a single mutual inductance
(K) statement. This video shows how to
define a transformer using inductors and
specify the mutual inductance via a single
K statement in your LTspice IV simulations.
Two new LTspice IV how-to videos are now available
Transformers
3rd-Party Models
What is LTspice IV?
LTspice® IV is a high performance SPICE
simulator, schematic capture and waveform
viewer specifically designed to speed up 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.
26 | January 2012 : LT Journal of Analog Innovation
Adding Third-Party Models to LT spice IV
video.linear.com/97
• LTM8047: 3.1V to 32V isolated µModule
DC/DC converter www.linear.com/8047
LTspice IV includes models for many discrete components, such as transistors and
MOSFETs, but many component manufacturers make additional models that you
can add to your LTspice IV circuit simulations. These third-party SPICE models are
described in .MODEL and .SUBCKT statements. This video provides an overview of
how to add a third-party .MODEL statement for an intrinsic SPICE device and
how to add and create a symbol for
a third party .SUBCKT statement.
Switching Regulators
• LTC3765: Active clamp forward controller
and gate driver www.linear.com/3765
• LTC3766: High efficiency, secondary-side synchronous forward
controller www.linear.com/3766
• LT®3759: Wide input voltage range
boost/SEPIC/inverting controller
www.linear.com/3759
• LTC3536: 1A low noise, buck-boost
DC/DC converter www.linear.com/3536
NEW LTspice DEVICE
MACRO MODELS
• LT3507A: Triple monolithic step-down regulator with LDO www.linear.com/3507A
To update your installation of
LTspice IV with the latest models, choose
Sync Release from the Tools menu. You
can review the changelog.txt after Sync
Release for the complete list of new models. Here is a list of some new models:
Linear Regulators
• LT3015: 1.5A, low noise, negative linear regulator with precision
current limit www.linear.com/3015
Amplifiers & Comparators
• LT6108: High side current sense
amplifier with reference and
comparator www.linear.com/6108
µModule Regulators
• LTM8048: 3.1V to 32V input isolated
µModule DC/DC converter with LDO post
regulator www.linear.com/8048
• LTC6360: Very low noise singleended SAR ADC driver with true zero
output www.linear.com/6360
4.7µH
SW1
VIN
VIN
1.8V TO 5.5V
SW2
VOUT
47pF
LTC3536
10µF
PWM BURST
OFF ON
MODE/SYNC FB
SHDN
RT
VC
PGND SGND
VOUT
3.3V
1A FOR VIN ≥ 3V
6.49k
49.9k
1000k
220pF
22µF
221k
Download the LTspice IV
demonstration circuit for this
1A low noise, buck-boost
DC/DC converter at www.
linear.com/3536
design ideas
HOW TO USE THE .STEP COMMAND TO PERFORM REPEATED ANALYSIS
There are two ways to examine a circuit
by changing the value for a particular
parameter: you can either manually enter
each value and then resimulate the circuit
to view the response, or use the .step
command to sweep across a range of
values in a single simulation run.
The .step command causes an analysis to
be repeatedly performed while stepping
through a model parameter, global
parameter or independent source. Here
is an example waveform response of an
RC circuit, for which the capacitance is
stepped through three values.
To implement this in LTspice IV, perform
the following steps:
Define the component parameter with
a variable by editing the component
attribute (Ctrl–right-click on the
component) and entering “{X}” for the
Value, where “X” is a user defined
variable name. The addition of the curly
braces around the variable is important as
it tells LTspice IV that “X” is a parameter.
Add a .step command via a SPICE
directive that specifies the steps for the
parameter “X” by a linear, logarithmic or
list of values.
Example A: “.step param X list .1u .2u
.3u” steps the parameter X through each
value listed.
Example B: “.step param X .1u .3u .1u”
steps the parameter X from 0.1u to 0.3u
in 0.1u increments.
For more information on how to use
the .step command to improve your
understanding of a schematic, review the
Help Topics in LTspice IV.
Happy simulations!
LTspice IV Power User Tip
NEW LTspice IV DEMO CIRCUITS
The LTspice IV circuit collection is available at www.linear.com/DemoCircuits.
Here are some of the new demonstration circuits now available:
SOLAR PANEL INPUT
<40V OC VOLTAGE
16V PEAK POWER VOLTAGE
MBRS140
10µF
MBRS340
LT3652
VIN_REG
Switching Regulators
SHDN
• LTC3618: Dual monolithic synchronous step-down converter for
DDR termination (2.25V–5.5V to
VDDQ at ±3A, VTTR at ±10m A, VTT at
±3A) www.linear.com/3618
CHRG
• LTC3617: Monolithic synchronous
step-down regulator for DDR termination (2.25-5.5V to VTTR at 10m A,
VTT at ±6A) www.linear.com/3617
• LTC3536: 1A low noise, buck-boost
DC/DC converter (1.8V–5.5V to 3.3V at
1.0A) www.linear.com/3536
Battery Charger
• LT3652: 1A solar-panel-powered 3-stage 12V lead-acid fast/
float charger (10V–16V to 12V at
1A) www.linear.com/3652
SW
VIN
499k
100k
1µF
BZX84C6V2L
BOOST
1N914
SENSE
BAT
FAULT
NTC
TIMER
VFB
L1
22µH
SYSTEM
LOAD
0.1Ω
910
10µF
309k
+
100µF
174k
+
4.7µF
1M
1N4148
L1: WURTH 7447779122
12V LEAD
ACID BATTERY
10k
100k
B = 3380
muRata
NCP18XH103
The LTspice IV demonstration circuit for this 1A solar-panel-powered 3-stage 12V lead-acid fast/float charger
is available at www.linear.com/3652
Linear Regulators
• LT3032: Dual 150m A Positive/Negative
Low Noise LDO Linear Regulator
(5V to 3.3V at 0.15A & –5V to –3.3V at
0.15A) www.linear.com/3032
• LT3015: 1.5A, low noise, negative linear regulator with precision current limit (–7V to –5.0V at
–1.5A) www.linear.com/3015 n
• LT3029: Dual 500m A /500m A LDO,
low noise, µpower linear regulator
(3V to 1.8V at 0.5A & 3V to 1.5V at
0.5A) www.linear.com/3029
The demonstration circuit for this1.5A, low noise, negative linear regulator
with precision current limit is available at www.linear.com/3015
GND
SHDN
VIN
–5.5V TO
–30V
3.40k
1%
LT3015
10µF
IN
10µF
ADJ
OUT
10.5k
1%
VOUT
–5V
–1.5A
January 2012 : LT Journal of Analog Innovation | 27