BD60A00NUX_12 Datasheet, PDF (8/25 Pages) Rohm – White LED Driver

BD60A00NUX
BD60A60NUX
Datasheet
●Protection
・Over voltage protection
At such an error of output open as the output DC/DC and the LED is not connected to IC, the DC/DC boosts too much
and the VOUT terminal exceeds the absolute maximum ratings, and may destruct the IC. Therefore, when the VOUT
becomes sensing voltage or higher, the over voltage limit protection works, turns off the switching Tr, DC/DC will be
stopped, and the output voltage goes down slowly. When output voltage becomes below the hysteresis voltage of Over
voltage protection, A boost function works and output voltage reaches detection voltage again.
This operation is repeated unless the abnormalities in application are recovered.
・Schottky Diode open protection
In the case of external SBD is not connected to IC, or VOUT is shorted to GND, the coil or internal Tr may be destructed.
Therefore, at such an error as VOUT becoming 0.2V or below, turns off the output Tr, and prevents the coil and the IC
from being destructed.
And the IC changes from activation into non-activation, and current does not flow to the coil (0mA).
・Thermal shut down
This IC has thermal shut down function.
The thermal shut down works at 175˚C or higher, and the IC changes from activation into non-activation.
・Over Current Protection
Over current flows the current detection resistor that is connected to between internal switching transistor source and
GND. Current sense voltage turns more than detection voltage, over current protection is operating and it is prevented
from flowing more than detection current by reducing ON duty of switching Tr without stopping boost.
As over current detector of This IC is detected peak current, current more than over current setting value does not flow.
SW
+
-
< The estimate of the current value which need for the normal operation>
As over current detector of This IC is detected the peak current, it has to estimate peak current to flow to the coil by
operating condition.
In case of, ○ Switching frequency = fsw Typ.=0.6MHz
○ Supply voltage of coil = VIN
○ Inductance value of coil = L
○ Output voltage = VOUT
○ Total LED current = IOUT
○ Average current of coil = Iave ○ Peak current of coil = Ipeak
○ Efficiency = eff
○ ON time of switching transistor = Ton
Ipeak = (VIN / L) × (1 / fsw) × (1-(VIN / VOUT))
Iave=(VOUT × IOUT / VIN) / eff
Ton=(Iave × (1-VIN/VOUT) × (1/fsw) × (L/VIN) × 2)^1/2
As peak current varies according to whether there is the direct current superposed, the next is decided.
(1-VIN/VOUT) × (1/fsw) < Ton
peak current = Ipeak /2 + Iave (continuous mode CCM)
(1-VIN/VOUT) × (1/fsw) > Ton
peak current = (VIN / L)×Ton (discontinuous mode DCM)
(Example 1)
In case of, VIN=6.0V, L=10µH, fsw=0.6MHz, VOUT=32.5V, IOUT=25mA, current =85%
Ipeak = (6.0V / 10µH) × (1 / 0.6MHz) × (1-(6.0V / 32.5V)) =0.82 A
Iave = (32.5V × 25mA / 6.0V) / 85% = 0.16A
Ton = (0.16A × (1-6.0V / 32.5V) × (1 / 0.75MHz) × (10µH /6.0V) × 2)^1/2 = 0.85µs
(1-VIN/VOUT) × (1/fsw)=1.36µs > Ton
peak current = (6.0V / 10µH)×0.85µs =0.51A
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TSZ02201-0G3G0C200320-1-2
27.SEP.2012 Rev.001