Ramp Load

The Ramp Load subcircuit models a single, non-repeating ramp or step in load current using a resistor and a PWL current source.

The resistor models the starting, or minimum, load current.
The PWL current source models the ramp portion of the load current.

The Ramp Load subcircuit is used in the StepLoad() test objective. You can change any managed DVM load to use the Ramp Load by entering a Ramp() entry in the Load column.

Other similar loads include the following:

Ramp Pure Load - a ramped load where both the starting current and the ramp current are modeled with a current source.
Pulse Load - Single Current Pulse - a single current pulse load with the starting current modeled with a resistor
Pulse Load - Single Pure Current Pulse - a single current pulse load with the starting current modeled without a resistor

In this topic:

Model Name

Ramp Load

Simulator

This device is compatible with both the SIMetrix and SIMPLIS simulators.

Parts Selector
Menu Location

DVM > Loads > DVM Output Load - 2 Terminal
DVM > Loads > DVM Output Load - 3 Terminal
DVM > Loads > DVM Output Load - 4 Terminal

Symbol Library

None - the symbol is automatically generated when placed or edited.

Model File

SIMPLIS_DVM_ADVANCED.lb

Subcircuit Names

SIMPLIS_DVM_ADVANCED_LOAD_2T_RAMP
SIMPLIS_DVM_ADVANCED_LOAD_3T_RAMP
SIMPLIS_DVM_ADVANCED_LOAD_4T_RAMP

Symbols

Schematic - 2 Terminal

Schematic - 3 Terminal

Schematic - 4 Terminal

Parameters

The table below explains the parameters used in the Ramp Load subcircuit.

Parameter Name	Default	Data Type	Range	Units	Parameter Description
FINAL_CURRENT	750m	Real	min: 0	A	The final current for the PWL current source portion of the load. The Ramp Load continues at this current for all simulation times greater than TIME_DELAY + RISE_TIME. This can be a numeric value or a symbolic value, such as a percentage of full load.
LOAD_NAME	LOAD	String	n/a	n/a	Name of the DVM load. This name cannot contain spaces.
LOAD_RESISTANCE	2.00667	Real	min: 0	Ω	The resistance value which models the starting current of the load
RISE_TIME	100u	Real	min: 0	s	The ramp rise time in seconds
START_CURRENT	0	Real	min: 0	A	The starting current for the PWL current source portion of the load. This is typically set to 0 since the minimum load current is modeled with the LOAD_RESISTANCE parameter. This can be a numeric value or a symbolic value, such as a percentage of full load.
TIME_DELAY	10u	Real	min: 0	s	The time delay before the ramp initiates

Testplan Entry

To set any managed DVM load to a Ramp Load subcircuit, place a Ramp() testplan entry in the Load column.

The Ramp() testplan entry has the following syntax with the arguments explained in the table below.

Ramp(REF, I_START, I_FINAL)
Ramp(REF, I_START, I_FINAL, OPTIONAL_PARAMETER_STRING)

Argument	Range	Description
REF	n/a	The actual reference designator of the DVM load or the more generic syntax of OUTPUT:`n` where `n` is an integer indicating a position in the list of managed DVM loads.
I_START	min: 0	The starting current for the load. This can be a numeric value or a symbolic value, such as percentage of full load.
I_FINAL	min: 0	The final current for the load. This can be a numeric value or a symbolic value, such as a percentage of full load.
OPTIONAL_PARAMETER_STRING	n/a	Parameter string with timing parameters TIME_DELAY and/or RISE_TIME*

* If both parameters are specified, join the two parameter key-value pairs with a space, as shown in the example below. The order of the parameter names does not matter.

DVM calculates the LOAD_RESISTANCE parameter from the ???MATH???I_{START}???MATH??? argument and subtracts the equivalent starting current from the PWL portion of the load. The calculation for the LOAD_RESISTANCE parameter is based on the following:

The nominal output voltage which is entered in the Output page of the Full Power Assist DVM control symbol.
The starting load current given in the Ramp() function or the StepLoad() objective.

Note: If the specified starting current is 0 and the load is configured by DVM using either a Ramp() function or the StepLoad() test objective, DVM replaces the Ramp Load subcircuit with a Ramp Pure Load subcircuit. The Ramp Pure Load does not use a parallel resistance to model the starting current.

Timing

During a StepLoad() test, DVM sets the output under test to use the Ramp Load subcircuit. Then DVM sets the TIME_DELAY and RISE_TIME parameters for the Ramp Load. You can change the timing with the Ramp() function call by providing the timing parameters as an optional parameter string, which is the fourth argument to the Ramp() function call.

Example

The following example sets the first DVM managed load to a Ramp Load with a starting current of 1A and a final current of 5A.

Note: In this example, the Load column is the first column in the testplan and, therefore, begins with the special three character sequence: *?@.

*?@ Load
Ramp(OUTPUT:1, 1, 5, TIME_DELAY=25u RISE_TIME=100u)

The results of this testplan entry are shown below:

Annotation	Value
X0	TIME_DELAY
X1	TIME_DELAY + RISE_TIME
Y0	I_START(see note below)
Y1	I_FINAL (see note below)

Note: The actual load current depends on the LOAD_RESISTANCE parameter and the actual time-varying load voltage. The I_START current is modeled by a resistor with a resistance equal to the value of LOAD_RESISTANCE . The PWL current source has points defined by the START_CURRENT and FINAL_CURRENT parameter values.