While designing a microcontroller board for a clients product, I came across a requirement where in the microcontroller was needed to drive a load with a current requirement around 100mA from a single output pin. But the microcontroller output pin is not capable of driving such a high current through the load.
Now the questions.
Wasn't it possible to drive it using a simple Low side driver with a NPN transistor?
No, it was not possible to use a low side driver because the load was a bunch of LED's with their cathode already connected to ground. To activate the LED's the anode pins of LED's should be connected to +3.3V. This needs to be done using a high side driver which when enabled connects the anodes of LED's to +3.3V.
What is the most common solution for a high side switch?
Its more common to use a PNP transistor or a P-channel mosfet as a high side driver. But these are not easily driven by a microcontroller and consume more space on PCB for biasing and stuff. These are not suitable for driving loads higher than the microcontrollers operating voltage.
Which solution i used?
While looking for high side switching options in mouser website, i came across AAT4280A. It is nice low cost high side load switch which fits perfectly into my application with a very small size.
AAT4280A can switch from 1.5V to 6V DC and can be directly driven by microcontroller and supports CMOS and TTL voltage levels at input control. The On/Off control can be used to switch the power ON/OFF to the load.
Here is how i connected this load switch to the TFT backlight LED input
The AAT4280A is a P-channel MOSFET power switch designed for high-side load switching applications. The device has a typical RDS(ON) of 80mOhm, allowing increased load switch power handling capacity.
Cost is only $0.17 = Rs.10/- per peice. If you order from Aqtronics, you will get it at Rs.17/-.
For how to order from Aqtronics, look at Where to buy electronics components in India?
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