I have a display with the backlight LEDs arranged 6S4P (so 4 parallel strings of 6 LEDs joined internally, so must be driven as single string) and have been trying to find a suitable driver for it - I thought the TPS61169 looked promising but now I've run the numbers I think I'm busting the 1.2A switch current limit.
Using TI's reference circuit & calculations from the datasheet (plus measured voltage on an example screen):
- Vin = 5v
- Total LED voltage (converter Vout) = ~26V
- Total LED current (Iout) = 240mA
- Assuming ~80% efficiency
- Inductor = 10uH
- Switch frequency = 1.2MHz (fixed)
- VFB = 204mV
- Diode Vf = 0.5v
- Sense resistor (RLED) = 0R85
- Input current (ILDC) = 1560mA
- Inductor ripple current (ILP-P) = 337mA
- Peak inductor current (ILP) = 1728mA
So assuming ILP will flow through the switch that's going to let the magic smoke out of the IC.
So, are my calculations correct? If so, without wanting to violate the "no shopping questions" rule, pointers to a more suitable device (ideally in the same footprint) would be most appreciated.