SOT-26 linear LED driver for strings up to 36V

The company describes AL5819, as it is known, as “ideal for 5V, 12V, and 24V LED lamps and strips”.

Vin and the top of the LED string can be the same or different – mixing and matching over 5-36V and 100mV to 36V respectively.

Current sensing is though a fixed internal low-value resistor, and current setting is via a more manageable value external resistor (diagrams) – the calculation is R=1,500/current, so 15k for 100mA, and there is a 200mA limit for values down to 0Ω.

Dimming is possible by adjusting this resistor or pulse-width modulating it using a series transistor – the data sheet shows values between 200Hz to 1kHz being used.

Drop-out is 250mV up to 60mA, and the company points out that more than one device can be paralleled for more current or power.

Heat removal is largely down the the legs of the 3 x 3mm footprint SOT26 package and, with such a tiny package, heat can easily be the limiting factor for current and voltage handling.

Local copper area will set the regulator’s power limits – on a 1 x 1inch square of 2oz FR-4 MPR substrate, said the company, junction to ambient resistance is 143°C/W.

De-rating starts at Tj=25°C and drops linearly to 145°C, with current limiting starting at 135°C. All current is stopped at +165ºC and will re-start at 145ºC. Official operating range is -40 to +125°C.

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