6 A Load Switch with Voltage Detector
April 9, 2019
The R5542 is a versatile load switch embedded in an ultra-small wafer level chip scaled package and is able to switch currents up to 6 A. The purpose of a load switch is to switch a power supply rails by an electronic switch; such kind of solution is smaller and less external components compared to FET. Because load switches have various additional features which are not available in FET.
In practice, the R5542 is positioned in between the battery or other supply voltage and the actual application circuit (load). The internal on-resistance is only 9 mΩ and will cause almost no voltage drop between input and output, in this way the power dissipation of the chip is kept to a minimum. The actual switching element of the R5542 consists of an N-Channel MOSFET and is controlled by the LCE input to switch off the power rails. Other advantages of a load switch are the possibility to set up a specific power-on sequence of various power supplies but also the total BOM count and total required board-space is significantly reduced compared to using discrete components in an equivalent circuit. As for the current consumption, the load switch consumes Typ.10 µA in On-mode and 1 µA in Off-mode.
The load switch has a number of safety circuits, like a reverse current protection to prevent a reverse current flow from the output to the input. This feature is only available when the LCE pin disables the load switch. Another Under Voltage Lock Out or UVLO function is present which disables the chip when the input voltage is below certain threshold voltage. In addition, the R5542 has a soft-start circuit to switch the load switch smoothly and to reduce inrush current.
The R5542 has an additional voltage detector on board which makes it possible to control the load switch when falling below a specific voltage threshold. All voltage detector terminals are isolated from the load switch, meaning that it can be configured and powered independently (by the VDI input). A delay can be created on the output by adding a resistor and capacitor on the VDO output. One can select the threshold in a range from 2.0 to 5.0 V in a 0.1 V step, this setting is internally fixed and does not require any external components. A practical example is that the voltage detector measures the load switch input voltage and disconnects it when this voltage drops below a certain level. Various other configurations are possible as well. (If this function is redundant, disabled the function is possible.)
The ball pin configuration of the WLCSP package is convenient according to electronics designers; all pin functions are accessible from the outer pins, which makes it easier to design the circuit board layout.
The new R5542 is a convenient tool with a powerful integrated MOSFET driver to switch the supply rails of the application while hardly occupying any board-space due to the small sized chip scaled package. Moreover, the protection circuits increase the safety level of the power supply. Most important is the achievement to reduce the total BOM count and to save mounting space.