Using a load switch instead of a regular mosfet offers several features including simplified design, small footprint, and protection features. In such systems, all but the most crucial of circuitry is removed from the battery output. Use smart load switches for current limit protection. A number of highside load switches can be used to disconnect unused loads and save power. A primer on highside fet load switches part 2 of 2. Pchannel mosfets, the best choice for highside switching.
By qi deng, senior product marketing manager, mixedsignal products. The definition of a highside load switch is that it is controlled by an external enable signal, and connects or disconnects a power source. To put it in perspective, the power dissipation of the load resistor is 5 watts. A primer on highside fet load switches part 1 of 2 ee. To return gate control to a more acceptable logic format, add an nchannel mosfet figure 3. When the wall unit power supply is connected to vin, the load is disconnected from the battery by a fully isolated switch which allows the load voltage to fluctuate. What are they, why do you need them and how do you. Figure 4 illustrates this approach, where a bottom nchannel fet, with its gate tied to the gate control core and its drain tied to the load, is turned on to discharge the capacitive load when the main switch, the top pchannel, is turned off. High side switch load driving safe inductive and capacitive load driving through integrated clamp and adjustable current limiting while the smart high side switch is current limiting there is a large amount of power dissipation. Load switch options the many possible applications for load switches let the load switch manufacturers offer multiple load switch configurations. The gate driver charges and discharges the gate of the fet in a controlled manner, thereby controlling. To narrow down on which fet we would use we can start by saying we want a part.
The definition of a highside load switch is that it is controlled by an external enable signal, and connects or disconnects a power source battery. The schematic shows body diodes which are part of every mosfet reminding that mosfets cannot provide a reverse current protection. The highside load switch often is used in applications in which battery life is very important. A primer on highside fet load switches part 1 of 2 ee times. Getting ntype performance out of ptype fets has meant larger area. A primer on highside fet load switches part 2 of 2 ee times. Nxp semiconductors an14 mosfet load switch pcb with thermal measurement mosfet based highside load switch is depicted in figure 2. When using a pchannel mosfet in a load switch circuit. Edn a primer on highside fet load switches part 2 of 2. An53 micropower high side mosfet drivers pdf analog devices. When using a p channel mosfet in a load switch circuit.
Like it sounds, this is a circuit that switches the high side or positive voltage to a load. Highside load switches are highly integrated power switches used to connect and disconnect a power source from a load. Sot235 power switch ics power distribution are available at mouser electronics. An14 mosfet load switch pcb with thermal measurement. Edn a primer on highside fet load switches part 1 of 2. Using a load switch instead of a regular mosfet offers several features. For r3 calculate the cic value, assume that it gives b. Using a pchannel mosfet may place some severe restraints on the gate drive, since the gate must be close to v dd figure 1b. An804 pchannel mosfets, the best choice for highside switching. Highside load switches and their operations continue to be popular choices for many engineers and designers, for applications including batterypowered portable devices such as featurerich mobile handsets, mobile gps equipment, and consumer entertainment gadgets.
The adp198 is a highside load switch designed for operation between 1. This is because v ds is large and the charging current is flowing through the switch. A useful circuit to have in designers toolbox is the high side switch. This article takes an easytounderstand and nonmathematical approach to explain the various aspects mosfet based highside load. Used as a highside switch, a pchannel mosfet in a totempole. Block diagrams of the mic94060123 pchannel, highside, load switches. A basic load switch such as the nx3p190 from nxp figure 3 resembles the circuit in figure 1 it has the pchannel mosfet controlled by a levelshifting and slewrate control circuit. Using an nchannel mosfet in this way simplifies the gate drive for a highvoltage, highside, pchannel mosfet. At the heart of any load switch is a mosfet usually an enhancement. Highside load switches protect portable electronic systems. Highside load switches are highly integrated power switches used to connect and disconnect.
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