LM3433SQ-36AEV/NOPB National Semiconductor, LM3433SQ-36AEV/NOPB Datasheet - Page 2

• Manufacturer Part Number: LM3433SQ-36AEV/NOPB
• Description: BOARD EVALUATION FOR LM3433SQ
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM3433SQ-36AEV/NOPB

• Current - Output / Channel: 30A
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 6V
• Features: Dimmable
• Voltage - Input: -9 ~ -14V
• Utilized Ic / Part: LM3433
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM3433SQ-36AEV

www.national.com
the LM3433 has enough internal drive current capability to
drive the dimming FETs without the use of external compo-
nents. The R
be slower but all related components could be removed. In
this case R14 should be loaded and the following components
may be removed: U5, U6, R33, D6, C22, and C25.
Alternatively if a high voltage gate driver is used (VCC = |VEE|
+ Vf where Vf if the LED forward voltage drop) then D5 and
C23 may be added to power the gate driver IC directly with
the charge pump and U6, D6, and C25 may be removed.
High Current Operation and
Component Lifetime
When driving high current LEDs, particularly when PWM dim-
ming, component lifetime may become a factor. In these
cases the input ripple current that the input capacitors are re-
quired to withstand can become large. At lower currents long
life ceramic capacitors may be able to handle this ripple cur-
rent without a problem. At higher currents more input capac-
itance may be required. To remain cost effective this may
require putting one or more aluminum electrolytic capacitors
in parallel with the ceramic input capacitors. Since the oper-
ational lifetime of LEDs is very long (up to 50,000 hours) the
longevity of an aluminum electrolytic capacitor can become
the main factor in the overall system lifetime. The first con-
sideration for selecting the input capacitors is the RMS ripple
current they will be required to handle. This current is given
by the following equation:
The parallel combination of the ceramic and aluminum elec-
trolytic input capacitors must be able to handle this ripple
current. The aluminum electrolytic in particular should be able
DS(ON)
will increase and the switch transitions will
2
to handle the ripple current without a significant rise in core
temperature. A good rule of thumb is that if the case temper-
ature of the capacitor is 5°C above the ambient board tem-
perature then the capacitor is not capable of sustaining the
ripple current for its full rated lifetime and a more robust or
lower ESR capacitor should be selected.
The other main considerations for aluminum electrolytic ca-
pacitor lifetime are the rated lifetime and the ambient operat-
ing temperature. An aluminum electrolytic capacitor comes
with a lifetime rating at a given core temperature, such as
5000 hours at 105°C. As dictated by physics the capacitor
lifetime should double for each 7°C below this temperature
the capacitor operates at and should halve for each 7°C
above this temperature the capacitor operates at. A good
quality aluminum electrolytic capacitor will also have a core
temperature of approximately 3°C to 5°C above the ambient
temperature at rated RMS operating current. So as an exam-
ple, a capacitor rated for 5,000 hours at 105°C that is oper-
ating in an ambient environment of 85°C will have a core
temperature of approximately 90°C at full rated RMS operat-
ing current. In this case the expected operating lifetime of the
capacitor will be approximately just over 20,000 hours. The
actual lifetime (Life
Where Life
perature T
85°C the core temperature is 85°C + 5°C = 90°C. (105°C -
90°C)/7°C = 2.143. 2^2.413 = 4.417. So the expected lifetime
is 5,000*4.417 = 22,085 hours. Long life capacitors are rec-
ommended for LED applications and are available with rat-
ings of up to 20,000 hours or more at 105°C.
CORE
RATED
. For example: If the ambient temperature is
is the rated lifetime at the rated core tem-
ACTUAL
) can be found using the equation: