1 Small Signal Division October 2013 Simulating with ON Semi CCR Models in SPICE By: Travis Alexander October 2013.

1 • Small Signal Division • October 2013

Simulating with ON Semi CCR Models in SPICE

By: Travis AlexanderOctober 2013

Small Signal Division

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.

Small Signal Division

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.

Valid schematic for NSI50150AD with Radj = 4Ω. For this part, yields ~350mA.

Small Signal Division

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.

• 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, over-voltage then transfers to higher current device, overheats, and burns out. Both CCRs are lost.

Tolerances cause practical problems with series CCRs, but cannot be easily replicated in simulations.

One useful way to connect CCRs in series is with parallel zeners—shown below.

Small Signal Division

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).

Small Signal Division

LTSpice Symbols & ModelsModels:• 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

Small Signal Division

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!

Small Signal Division

For additional questions and support, please contact:

Travis AlexanderMarketing & Applications Engineering Intern5005 E. McDowell Rd, Phoenix, AZ 85008

Email: [email protected]: (602) 244-5823

Thank you!