1. WEBENCH Schematic Editor Hands On Problems
Configuring Input and Load Transient Simulations

2. Hands-on Exercise: Perform Load Transient Simulation In Editor/Simulator
Design Problem:
Goals:
Create the following design:
Device: LM2735X
Vin: V
Vout: 12V
Iout: 0.5A
Edit the design using the WEBENCH Editor/Simulator and create a load transient simulation using the following load parameters:
Initial current (I1): 0.25A
Pulsed current (I2): 0.5A
Initial delay time (Td): 3.1msec
Rise time (Tr): 1usec
Fall time (Tf): 1usec
Pulse width (Pw): 0.5msec
Pulse period (Per): 1msec
Utilize WEBENCH Power Designer to create a boost design
Understand how to configure a load transient simulation in the WEBENCH Editor/Simulator
Extra credit: Add a 2nd load source and view the simulation results. 2

3. Why does the editor use startup as default?
Edited schematics always begin with a generic startup simulation
This is to enable the most versatile schematic with no initial conditions
In the normal WEBENCH Simulator, non startup simulations utilize initial conditions on Vout and other nodes to speed up stabilization time. But this is not possible in the editor since we do not know what the schematic topology will be after editing.
To do a transient simulation, add a pulsed (or other transient) source to the desired node
Note that sometimes a simulation model may not start up normally with a fixed current source
May need to add a small resistor in parallel
Can use voltage sources in series or current sources in parallel
Current sources in series may generate convergence errors

4. How to proceed
Create the LM2735 design and click the Edit button in the top navigation bar to edit the schematic.
Once in the editor, click on the Simulation button to run a simulation in the editor/simulator to see the behavior with a resistive load (startup).
Note the time it takes to start up.

5. Original Schematic with Resistive Load
Time to start up

6. Next steps Click the Edit button to begin the editing operations.
Delete the resistive load
Click on the Place Part menu and select Pulse Current Source to add it to the schematic
Rotate the new source so the polarity is correct (+ up)
Go to the simulator page and enter the transient parameters including a 3.1msec delay to allow the system to start up
Run a simulation to see the behavior with a pulsed current source (load transient).
Initial current (I1): 0.25A
Pulsed current (I2): 0.5A
Initial delay time (Td): 3.1msec
Rise time (Tr): 1usec
Fall time (Tf): 1usec
Pulse width (Pw): 0.5msec
Pulse period (Per): 1msec

7. Edited Load Transient Schematic
Delay time to allow startup before pulse

8. Extra Credit: Edited Schematic With 2 Loads In Parallel
Added 0V voltage source to probe total load current
2 load sources in parallel

9. Next steps Click the Edit button to begin the editing operations.
Click on the Place Part menu and select Pulse Current Source to add it to the schematic along with the connecting wires
Go to the simulator page and enter the transient parameters for the 2nd source including a 3.2msec delay to allow the system to start up
Also update the parameters for the original source
Run a simulation to see the behavior with a pulsed current source (load transient).
New Pulsed Current Source:
Initial current (I1): 0.1A
Pulsed current (I2): 0.05A
Initial delay time (Td): 3.2msec
Rise time (Tr): 1usec
Fall time (Tf): 1usec
Pulse width (Pw): 250usec
Pulse period (Per): 500usec
Original Pulsed Current Source:
Initial current (I1): 0.25A
Pulsed current (I2): 0.5A
Initial delay time (Td): 3.1msec
Rise time (Tr): 1usec
Fall time (Tf): 1usec
Pulse width (Pw): 750usec
Pulse period (Per): 1500usec

10. Waveforms with 2 Loads In Parallel

11. Hands-on Exercise: Perform Input Transient Simulation In Editor/Simulator
Design Problem:
Goals:
Create the following design:
Device: LM25011
Vin: 14-22V
Vout: 3.3V
Iout: 2A
Edit the design using the WEBENCH Editor/Simulator and create an input transient simulation using the going from 18V down to 14V:
Initial voltage (V1): 0V
Pulsed voltage (V2): -4V
Initial delay time (Td): 3.1msec
Rise time (Tr): 1usec
Fall time (Tf): 1usec
Pulse width (Pw): 0.5msec
Pulse period (Per): 1msec
Understand how to configure an input transient simulation in the WEBENCH Editor/Simulator 11

12. Configuring Input Transient Simulations
Input transients require that the startup input voltage source be supplemented by a pulsed voltage source.
This pulsed source needs to be configured in series with the startup source and should have a delay time so the pulse does not occur until after the part has been started up.

13. How to proceed
Create the LM25011 design and click the Edit button in the top navigation bar to edit the schematic.
Once in the editor, click on the Simulation button to run a simulation in the editor/simulator to see the behavior with a startup voltage source.
Note the time it takes to start up.
Add the additional pulsed voltage source in series with the existing startup source.
Go to the simulator page
Double click on the new source and configure the simulation parameters (see next pages)
Run a new simulation and note the behavior of the input and output voltages.

14. Initial configuration uses a startup voltage source on the input
Time to start up
Original startup source parameters:
Initial voltage (V1): 0V
Pulsed voltage (V2): 18V
Initial delay time (Td): 0.1msec
Rise time (Tr): 10usec
Simulations are normally configured for startup mode. Note the startup time so you can delay the pulse until after this.

15. Add Additional Pulsed Voltage Source
Add pulse voltage source
New pulsed voltage source parameters (in series with existing startup source)
Initial voltage (V1): 0V
Pulsed voltage (V2): -4V
Initial delay time (Td): 2.7msec
Rise time (Tr): 50nsec
Fall time (Tf): 50nsec
Pulse width (Pw): 0.1msec
Pulse period (Per): 0.2msec
If you would like to configure a transient on the input source you can add a 2nd pulse source in series with the original startup source. Configure the initial delay to be after the device starts up.
Pulsed Vin after startup

16. Simulation Results
Delay time to allow startup before pulse