Page Comparison

...

• We will likely be using parallel led strings (this is pretty common in lights now days) so we need a good way to deal with this. We want to balance led strings. One example would be if there are leds in parallel and they have a forward voltage of 3.3V, since there is up to 20% variation it could be a huge difference in the voltage needed. Additionally, the lower voltage draws more current than expected compared to the higher voltage string.

• In general, if temp goes up, the forward voltage will drop and it will draw a lot more current → we should mount on a common heat sink (I believe this is being done in the current boards)

• We can use a current mirror (this is being done in the current boards) for regulating current

• if using dimmable lights, pwm is the way to go

...

• Use independent opamps for each string instead of a current mirror, might have extra voltage but the current level should be good. More effective, less efficient, other considerations include needing a FET in a power package and that the switching frequency will be lower

• We could add balsast resistors though this is probably not needed since we are using the current mirrors

• Sounds expensive but using a mag-amp with one dc driver for dimmable leds

• Increase the FOV of the lights

• increase power efficiency

  • Vary threshold voltages (use low voltage thresholds)

  • stack transistors in series

  • if we are using linear regulators switch to switching regulators

    • we can use fast switching mosfets

  • add more thermal vias if possible.

  • Make sure we keep the ground and power planes for low impedance paths

  • Adding decoupling and bypass capacitors (for filtering) near power pins of components

  • Center high power components for better thermal efficiency

  • even thought the driver boards are small, try to keep things away from the edge of the board

  • if necessary add heat sinks

  • Test the current boards with a PDN analyzer?

PCB Layout Considerations

Cap near the supply voltage
check signal integrity
keep path length short

Notes for our led driver

• we can apply a 0.2V or lower to enter standby saving power

• choose low esr cap (place it as close to the IC as possible) (on avg 4.7 to 10uf)

• caps should be X7R or X5R for stability

• diode showld be fast low cap. schottky with low reverse leakage

Recommendations for minimizing radiated EMI and other transients and thermal considerations are:

1. The decoupling capacitor (C1) has to be placed as close as possible to the VIN pin and D1 Cathode

2. The freewheeling diode’s (D1) anode, the SW pin and the inductor have to be placed as close as possible to each other to avoid ringing.

3. The Ground return path from C1 must be a low impedance path with the ground plane as large as possible

4. The LED current sense resistor (Rs) has to be placed as close as possible to the VIN and SET pins.

5. The majority of the conducted heat from the AL8860Q is through the GND pin 2. A maximum earth plane with thermal vias into a second
   earth plane will minimise self-heating

6. To reduce emissions via long leads on the supply input and LEDs, low RF impedance capacitors should be used at the point where the
   wires are joined to the PC

Probable Upgrades

Add reverse polarity protection using PMOS transistor

...