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MBI1816
16-Channel Constant-Current LED Driver
November 2004, V1.00
- 7 -
OE
The maximum allowable package power dissipation is determined as PD(max) = (Tj – Ta) / Rth(j-a). When 16 output
channels are turned on simultaneously, the actual package power dissipation is PD(act) = (IDD x VDD) + (IOUT x Duty x
VDS x 16). Therefore, to keep PD(act) ≤ PD(max), the allowable maximum output current as a function of duty cycle is:
IOUT = { [ (Tj – Ta) / Rth(j-a) ] – (IDD x VDD) } / VDS / Duty / 16,
where Tj = 125
°C;
Duty= tON / T;
tON: the time of LEDs turning on; T:
signal period
*Note 1: The thermal resistor Rth(j-a) =117 °C/W; it is based on the following structure.
The PCB area L2xW2 is 4 times to the
IC
’s area L1xW1.
The thickness of the PCB is 1.6 mm,
copper foil 1 OZ. The thermal pad on the
IC
’s bottom has to be mounted on the
copper foil.
L1
W1
W2
L2
Copper foil
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