How to Simulate PROFET™ Load Guard 12V Capacitive Load Switching with PSpice
In automotive applications, there are input capacitors (ranging from hundreds of µF up to mF) which enables the module working reliably in case of voltage spikes or oscillations. The capacitive load switching (CLS) mode was implemented as a feature of PROFET™ Load Guard 12V devices to handle the initial inrush current of the capacitor and charge bigger capacitors, without triggering protection function. This behavior can be studied using the PSpice simulation model.
How to set up the testbench?
The easiest way is to download the simulation model from the Infineon website and start from the predefine testbench.
In order to enable the CLS mode on the input pin, a PWM signal should be applied with the specified frequency and duty cycle from the datasheet (freq=30kHz, duty cycle=50%). In PSpice this can be done with a VPULSE source by defining the parameters like in the Figure 2. The Pulse Width and Time Period should be calculated based on frequency and duty cycle needed to enable the CLS mode.
The load is described taking in account the important specifications of a real capacitor, parasitic resistors, ESR in series with the capacitor and a parallel resistor. This can be easily modified by the user in order to see the behavior for different types of loads ranging from hundreds of µF up to mF. When you change it, you may also have to adapt the simulation time to see the capacitor fully charged.
How to interpret the simulation results?
After setting up the testbench is time to run the simulation. If you need more details about creating a simulation profile and simulate, check PSpice Getting Started document form the model package.
Some points about the results:
- First plot consists in the PWM signal with 30kHZ frequency and 50% duty cycle;
- In the second plot, we can see the output voltage that indicates the capacitor charging in steps;
- Third plot represents the output current: the capacitor is charged by pumping current in order to avoid latching OFF the device;
- In the fourth plot, is the thermal behavior of the device. Dynamic overtemperature protection is reduced to a lower value with continuous restart, doing so the current pumping method is applied on the load without reaching very high temperatures.
Also with the simulation model some electrical parameters can be measured in typical conditions:
- Current limitation set by the OCT pin;
- CLS activation and de-activation delays;
- Thermal shutdown temperature.
Simulate online on Infineon Designer
The testbench presented in this article can be found online on Infineon Designer. It can be simulated as it is or login into an account and adapt to your application requirements.