EYE ON NPI - Nexperia NPS4053 5.5 V Load Switch

This week's EYE ON NPI will take a load off your mind, it's Nexperia's NPS4053 5.5 V Load Switch (https://www.digikey.com/en/product-highlight/n/nexperia/nps4053-5_5-v-load-switch) - it's Nexperia's first load switch and they did a great job with the NPS4053 which can be used for a variety of situations where you want to separate power supplies for protection or power savings. I'll admit, I've never used a load switch chip before - so this EYE ON NPI was a bit of a learning experience. Traditionally we've used 3 major ways to switch current. First is, of course, a simple switch - we use something like this on our QT Py Lipo BFF (https://www.adafruit.com/product/5397) where we want to allow mechanical switching and the amount of current isn't super high. The slide switch is specified for 300mA and we double-up the DPDT to allow for 600mA. This could be expanded upon with a power switch that can handle up to 240VAC and 5A (https://www.adafruit.com/product/3991) - but of course someone has to flip the switch. We could solve that issue by going with a relay or a solid-state-relay (https://blog.adafruit.com/2023/08/03/eye-on-npi-sensata-crydoms-series-1-ac-panel-mount-solid-state-relays-eyeonnpi-digikey-sensata-digikey-adafruit/) but they have some downsides as well: high cost, large space requirements. We need something much smaller! On our dev boards we have historically used two techniques for flipping on/off power to subcircuits. One is the P-FET high-side switch, which you can see on our Metro boards on the DC jack (https://www.digikey.com/short/d3j7z977). This method is classic, and works well but has a few downsides: you need a second transistor to control high voltages with a low voltage signal since the gate is pulled up to the high input voltage. Also, there's that built-in diode that is will conduct current from the output back to the input - you can see in our schematic how we also have to add a forward-diode to protect against that. Altogether, you would need 2 transistors, a diode and a couple resistors to make a FET-based switch. There's also another downside to FET switches, which is that they are not current limited, so if you happen to be switching a significant amount of current, it could cause a transitory spike on your main power supply...which causes a brownout! Something we experienced when we tried using a P-FET to switch on-off an I2C port. It worked great for low-current sensors but would crash the board when used with a 100mA-draw air quality sensor. So we used a fully separate LDO on the Feather ESP32-S2's (https://www.digikey.com/short/4nj457zb) - this works because we have a volt or more drop from the conversion from 5V to 3.3V so if there's a dip in the voltage, it isn't going to affect the main micro's power supply. This works because the LDO is only a few cents (https://www.digikey.com/short/fnr9jtnj), and we happen to have the headroom. It also has true-disconnect (no extra diode needed!) and is compatible with lower voltage logic signals. But, most devices have a DC/DC converter which is going to be a lot larger than a SOT-23-5 LDO - and there might not be as much headroom. That's where the Nexperia NPS4053 5.5 V Load Switch (https://www.digikey.com/short/ttjt5mjw) comes in! It combines all the analog electronics you need to easily switch loads of up to 5.5V at 2A, with all the niceties that you'd normally have to manage by hand. Instead of a second diode, it has true-cutoff. Instead of a separate current-limiting circuit (https://en.wikipedia.org/wiki/Crowbar_(circuit)), you can set the current limiting with a resistor and the load switch will turn from Constant Voltage to Constant Current mode. The chip also handles transients nicely, with soft-start, so that you don't get a shock to the power supply if the sub-circuit turns on all at once! In addition, there's Under Voltage Lockouts and short circuit protection. If something does go wrong, the chip will disconnect the load and drive the FAULT pin low, so you can communicate to the user that something is amiss. For many of the short/temp/over-current errors, the chip will naturally recover. With an adorable 2x2mm HVSON package and a cost of only 20 cents in quantity, the Nexperia NPS4053 5.5 V Load Switch (https://www.digikey.com/short/ttjt5mjw) will fit into the same board slot as a transistor for not much more, and replace a ton of power management circuitry with elegant simplicity! And, best of all - it's in stock right now at DigiKey for immediate shipment, in both commercial/industrial (https://www.digikey.com/en/products/detail/nexperia-usa-inc/NPS4053GHZ/21286453) and Q100Z variants (https://www.digikey.com/en/products/detail/nexperia-usa-inc/NPS4053GH-Q100Z/21286452). Order today, then kick your feet up on an ottoman and take a load off: you can relax while DigiKey picks, packs and ships your order instantaneously so that you will have parts in hand by tomorrow morning.