78 Application Programs
Application 3. Controlling Output Voltage Ramp Up at Turn On
Overview Of Application
When control over the rate of voltage ramp up at turn-on of the power module output is required, the desired shape can be
approximated by downloading and executing a series of voltage and dwell time points.
For this example, you need to program the power module to change its output from 2 volts to 10 volts, slewing through the 8
volt transition in 0.5 seconds. This results in a turn-on ramp-up of 16 V per second.
The MPS can create this voltage versus time characteristic using Lists. The desired characteristic (in this case, linear) is
simulated using the 20 available voltage points. To determine the value of each point in the transition, simply divide the
change in voltage by 20. To determine the dwell time of each voltage point, divide the total transition time by 19. After the
List has been executed, the module will continue to output the final value (in this case, 10 volts) until the output has been
reprogrammed to another value. Note that the dwell-time of the last point is not part of the transition time.
To determine the slowest ramp up (longest transition time) that can be generated, you must consider how smooth you need
the voltage versus time characteristic to be. As the dwell time associated with each point gets longer, the output voltage will
become more like a "stair step" and less like a linear transition. (see Figure B3-1)
To determine the fastest ramp up (shortest transition time) that can be generated, you must consider the minimum dwell time
specification (10 ms) and the maximum risetime of specification the power module (20 ms). If you program 10 ms dwell
times, the power module will not be able to reach its output voltage before the next voltage point is output. (see Figure B3-
2)
MPS Features Used
•
20-point voltage List.
•
Dwell time.
•
Dwell-paced Lists.
Advantages/Benefits Of The MPS Solution
By using Lists, the module changes its output voltage automatically, so that the computer is not devoted to reprogramming
the output voltage.
The outputs can change faster when dwell paced than when the computer must explicitly reprogram each change.
The sequence is simpler to program (no timing loops). By using dwell times, the timing of each point is accurate and
repeatable.
The computer does not provide timing for the sequence. For negative-going ramps, the active downprogrammers in the
module output can quickly discharge the module’s output capacitors and any capacitance in the DUT when negative going
ramps are required.
Implementation Details
How the MPS Implements The Sequence
The module is programmed to List mode.
The module will execute a dwell-paced List.
The 20 voltage points are downloaded to the module.
The 20 dwell times are downloaded to the module.
When the transition must occur, the module is triggered by the computer.
The module output ramps under its own control.
