Download HowToUseCCRModels

Simulating with ON Semi
CCR Models in SPICE
By: Travis Alexander
October 2013
1 • Small Signal Division • October 2013
Simulating with CCRs
• All CCR models work for AC and DC sources.
• All CCR models are valid up to 1 MHz.
• CCRs may be placed in parallel with each other to
increase regulated current.
Sample DC schematic with
NSI50350ADT4G and LED.
Sample schematic for 120 Vac,
depicting bridge, CCR, and LEDs.
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Simulating Adjustable CCRs
• You may fine tune the Radj resistor until you achieve
desired current.
• To simulate “open” Radj, connect a >1 MΩ resistor between
Radj and cathode (K).
Valid schematic for NSI45035JZ with
Radj = Open. For this part, yields ~35mA.
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Valid schematic for NSI50150AD with
Radj = 4Ω. For this part, yields ~350mA.
Using CCRs in Series
• In simulation, series CCRs
appear to be a convenient way to
drop extra voltage.
• Practically, this is poor design,
as no two CCRs are the same.
Tolerances cause practical problems with series
CCRs, but cannot be easily replicated in simulations.
• Practical scenario:
– Series CCRs: At startup, total
current limited is by lower current
device. Excess voltage builds up
over lower device, eventually
overheats and shorts device, overvoltage then transfers to higher
current device, overheats, and burns
out. Both CCRs are lost.
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One useful way to connect CCRs in series
is with parallel zeners—shown below.
Thermal Considerations
• The models are designed to reflect steady-state behavior at
ambient temperature.
• Practically, CCRs also have a temporal NTC (negative
temperature coefficient) to help prevent thermal runaway.
• With actual hardware, the initial pulse current may measure
higher, and then settle over time.
A data sheet plot for the NSIC2050BT3G
depicts this NTC over time (shown right).
The simulation model for this device replicates
the steady-state behavior (post-NTC).
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LTSpice Symbols & Models
Models:
•
•
•
ON Semiconductor provides encrypted CCR device models for use in LTSpice.
By default, save encrypted model files (.sp) in the same directory with simulation
schematics (.asc).
When given an “Open” versus “Save” option for the file after downloading, try to pick
“Save.”
–
–
Files often undergo name changes when opened in temporary download folders, which can cause mapping
problems later. Choosing the direct “Save” option simplifies this process, even if a rename is required later.
Opening the file immediately upon download can also errors in the subcircuit definition in encrypted files. The cause
of this is not known.
Symbols:
•
•
ON Semiconductor provides symbols (.asy) for all LTSpice CCR models.
Save provided CCRs symbols folder in default symbols directory
–
Example: C:\Program Files\LTC\LTSpiceIV\lib\sym
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LTSpice Symbols Setup
(1) Download “CCRs.zip” from ON Semiconductor’s website.
(2) Extract and save in default symbols library (such as LTSpice\lib\sym) for simplest
integration.
(3) Close and re-open LTSpice to have your new CCR symbols library ready.
(4) Save any desired models to the directory containing the schematic (.asc). By
default, symbols map to models here.
(5) Simulate!
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Thank you!
For additional questions and support, please contact:
Travis Alexander
Marketing & Applications Engineering Intern
5005 E. McDowell Rd, Phoenix, AZ 85008
Email: [email protected]
Phone: (602) 244-5823
Small Signal Division