Hi. This presentation is titled "Beating Discrete Solutions with Integrated Loads Switches." For this portion of the presentation, we will be covering one of the topics-- inrush current management. Inrush current is a transient current drawn by the load capacitance of the system when first turned on. Depending on the amount of load capacitance, this can cause a large spike of inrush current that could cause the input supply to droop or cause damage to downstream components.

The figure in the top left shows an upstream power supply connected to a downstream load by a switch. When the switch is initially connected, the power supply is connected to the load. This sudden change in voltage will result in a spike of inrush current. The severity of the inrush current event will be determined by the input voltage, the amount of load capacitance, and the rate at which the load capacitor becomes charged.

Now, let's take a look at a few inrush current considerations to account for when choosing a switching solution. The rate at which the load capacitor becomes charged will determine the amount of inrush current. A faster rise time, as shown on the left, will result in a larger inrush current. With a slower rise time, as shown on the right, this will result in a lower inrush current.

The acceptable amount of inrush current varies from system to system. If the inrush current is too great, this can cause the input supply to dip, which could cause the system to reset or cause the current to damage the downstream load. Some factors to consider while determining the acceptable inrush current include the strength of the upstream power supply, the width of the board and PCB traces, rating of any connectors on the board, and the rating of the switch.

One disadvantage to this is discrete implementation is the nonlinearity of the inrush current. Since the ramp rate is dependent on the RC delay on the gate, the switch starts to turn on slowly and exponentially increases until the FET becomes fully on. This nonlinear dV dt of V out of the nonlinear inrush current spike.

For example, when comparing the discrete solution on the left to the integrated load switch solution on the right, both circuits are starting into the same [? 100-microfarad ?] load at 1.8 volts. However, the discrete solution causes a nonlinear 450-milliamp inrush current spike, while the integrated load switch solution limits the current to under 200 milliamps.

The last factor to consider is the power dissipation across the switch while turning on. If a switch has a controlled output rise time, then there's a large amount of power dissipation initially during turn-on. Initially, there will be the full voltage drop across the switch, and the power dissipation will be at the highest. As the output starts to rise in voltage, the power dissipation will start to decrease.

A faster turn-on will reduce the total energy dissipated in the switch from power dissipation, but the inrush current will rise. Done discretely, this power dissipation can be managed by looking at the SOA curve of the MOSFET, usually found in the MOSFET datasheet.

In summary, a discrete solution offers the benefits of customizing the inrush current by adjusting the various passive components. However, it also comes with various downsides, including a larger solution size and number of components, sometimes requiring three to six components to achieve the same functionality. Also, with the longer rise time, the design will also have a longer fall time. There's also a nonlinear turn-on behavior which can result in a larger spike of inrush current. And the power dissipation from large capacitor in rise time could damage the MOSFET solution.

In comparison, an integrated load switch offers an easy rise time functionality by adjusting a single external component. The number of components is also reduced, and the output will rise with the linear turn-on behavior. Even with the long rise time, the turn-off time can still be small due to a feature known as QOD, which we will discuss later. And some of the load switches come with features such as thermal shutdown, which prevent overheating damage during turn-on. One downside is that the peak current rating might be higher than in a discrete MOSFET solution.

In the next presentation, we will be discussing load protection during fall conditions.