LM3502SQX-35/NOPB National Semiconductor, LM3502SQX-35/NOPB Datasheet - Page 16

• Manufacturer Part Number: LM3502SQX-35/NOPB
• Description: IC LED DRIVR WHITE BCKLGT 16-LLP
• Manufacturer: National Semiconductor
• Series: PowerWise®r
• Type: Backlight, White LEDr

Specifications of LM3502SQX-35/NOPB

• Topology: PWM, Step-Up (Boost)
• Number Of Outputs: 2
• Internal Driver: Yes
• Type - Primary: Backlight
• Type - Secondary: White LED
• Frequency: 800kHz ~ 1.2MHz
• Voltage - Supply: 2.5 V ~ 5.5 V
• Voltage - Output: 33 V ~ 34 V
• Mounting Type: Surface Mount
• Package / Case: 16-LLP
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: 750mA
• Internal Switch(s): Yes
• Efficiency: 80%
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM3502SQX-35

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Application Information
DIODE SELECTION
To maintain high efficiency it is recommended that the aver-
age current rating (I
larger than the peak inductor current (I
mum, the average current rating of the diode should be
larger than the maximum LED current. To maintain diode
integrity the peak repetitive forward current (I
greater than or equal to the peak inductor current (I
Diodes with low forward voltage ratings (V
capacitance magnitudes (C
high efficiency. The chosen diode must have a reverse
breakdown voltage rating (V
than the output voltage (V
is chosen, Schottky or not, certain selection criteria must be
followed:
1. V
2. I
3. I
Some recommended diode manufacturers included but are
not limited to:
SHUTDOWN AND START-UP
On startup, the LM3502 contains special circuitry that limits
the peak inductor current which prevents large current
spikes from loading the battery or power supply. When Cntrl
≥ 1.4V and both the En1 and En2 signals are less than 0.3V,
the LM3502 will enter a low I
During this low I
below the supply voltage and the soft-start will be reset to
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On
Semiconductor
Central
Semiconductor
F
FRM
R
or I
and V
≥ I
O
Lpeak
≥ I
RRM
GMK212BJ105MD
(0805/35V)
GRM40-035X7R105K
(0805/50V)
C3216X7R1H105KT
(1206/50V)
C3216X7R1C475K
(1206/16V)
08053D105MAT
(0805/25V)
08056D475KAT
(0805/6.3V)
1206ZD475MAT
(1206/10V)
LOAD
Q
>
SS12(1A/20V)
SS14(1A/40V)
SS16(1A/60V)
MBRM120E
(1A/20V)
MBRS1540T3
(1.5A/40V)
MBR240LT
(2A/40V)
CMSH1- 40M
(1A/40V)
mode the output voltage is a diode drop
F
or I
V
or I
OUT
OUT
O
out
) of the selected diode should be
J
). No matter what type of diode
Q
or C
R
state and regulation will end.
and/or V
T
or C
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D
Lpeak
RRM
) are conducive to
F
(Continued)
) and low junction
) that is larger
). At the mini-
FRM
) must be
Lpeak
).
16
limit the peak inductor current at the next startup. When both
En1 and En2 are less than 0.3V, the P1 PMOS and N2
NMOS switches will turn off.
When Cntrl
will shutdown and the output voltage will be a diode drop
below the supply voltage. If the Cntrl pin is low for more than
12ms, the soft-start will reset to limit the peak inductor cur-
rent at the next startup.
When Cntrl is
device will not shutdown and reset the soft-start but shut off
the NMOS N1 Power Device to allow for PWM contrl of the
LED current.
THERMAL SHUTDOWN
The LM3502 stops regulating when the internal semiconduc-
tor junction temperature reaches approximately 140˚C. The
internal thermal shutdown has approximately 20˚C of hyster-
esis which results in the LM3502 turning back on when the
internal semiconductor junction temperature reaches 120˚C.
When the thermal shutdown temperature is reached, the
softstart is reset to prevent inrush current when the die
temperature cools.
UNDER VOLTAGE PROTECTION
The LM3503 contains protection circuitry to prevent opera-
tion for low input supply voltages. When Vin drops below
2.3V, typically the LM3502 will no longer regulate. In this
mode, the output volage will be one diode drop below Vin
and the softstart will be reset. When Vin increases above
2.4V, typically, the device will begin regulating again.
OVER VOLTAGE PROTECTION
The LM3502 contains dedicated circuitry for monitoring the
output voltage. In the event that the LED network is discon-
nected from the LM3502, the output voltage will increase
and be limited to 15.5V(typ.) for the 16V version , 24V(typ.)
for the 25V version, 34V(typ.) for the 35V version and
42V(typ.) for the 44V version (see eletrical table for more
details). In the event that the network is reconnected, regu-
lation will resume at the appropriate output voltage.
LAYOUT CONSIDERATIONS
All components, except for the white LEDs, must be placed
as close as possible to the LM3502. The die attach pad
(DAP) must be soldered to the ground plane.
The input bypass capacitor C
be placed close to the IC and connect between the V
PGND pins. This will reduce copper trace resistance which
effects input voltage ripple of the IC. For additional input
voltage filtering, a 100nF bypass capacitor can be placed in
parallel with C
ground. The output capacitor, C
the IC and be connected between the V
pins. Any copper trace connections for the C
can increase the series resistance, which directly effects
output voltage ripple and efficiency. The current setting re-
sistor, R1, should be kept close to the Fb pin to minimize
copper trace connections that can inject noise into the sys-
tem. The ground connection for the current setting resistor
network should connect directly to the PGND pin. The AGND
pin should be tied directly to the PGND pin. Trace connec-
tions made to the inductor should be minimized to reduce
power dissipation and increase overall efficiency while re-
ducing EMI radiation. For more details regarding layout
guidelines for switching regulators, refer to Applications Note
AN-1149.
<
0.3V for more than 12ms, typicaly, the LM3502
<
IN
0.3 but for less than 12ms, typically, the
to shunt any high frequency noise to
IN
, as shown in Figure 1, must
OUT
, must be placed close to
OUT1
OUT
and PGND
capacitor
IN
and