LM3559TLX/NOPB National Semiconductor, LM3559TLX/NOPB Datasheet - Page 38

• Manufacturer Part Number: LM3559TLX/NOPB
• Description: LM3559
• Manufacturer: National Semiconductor
• Series: -r

Specifications of LM3559TLX/NOPB

• Constant Current: Yes
• Constant Voltage: -
• Topology: High Side, PWM, Step-Up (Boost)
• Number Of Outputs: 2
• Internal Driver: Yes
• Type - Primary: Flash/Torch
• Type - Secondary: White LED
• Frequency: 1.8MHz ~ 2.2MHz
• Voltage - Supply: 2.5 V ~ 5.5 V
• Voltage - Output: -
• Mounting Type: Surface Mount
• Package / Case: 16-UFBGA
• Operating Temperature: -40°C ~ 85°C
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

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Layout Recommendations
The high switching frequency and large switching currents of
the LM3559 make the choice of layout important. The follow-
ing steps should be used as a reference to ensure the device
is stable and maintains proper LED current regulation across
its intended operating voltage and current range.
1.
2.
3.
Place C
and as close to the device as possible. The input
capacitor conducts the driver currents during the low side
MOSFET turn-on and turn-off and can see current spikes
over 1A in amplitude. Connecting the input capacitor
through short wide traces to both the IN and GND
terminals will reduce the inductive voltage spikes that
occur during switching and which can corrupt the V
Place C
and as close as possible to the OUT and GND terminal.
The returns for both C
at one point, and as close to the GND pin as possible.
Connecting C
the series inductance on the OUT and GND terminals
that can corrupt the V
excessive noise in the device and surrounding circuitry.
Connect the inductor on the top layer close to the SW pin.
There should be a low-impedance connection from the
inductor to SW due to the large DC inductor current, and
at the same time the area occupied by the SW node
should be small so as to reduce the capacitive coupling
of the high dV/dt present at SW that can couple into
nearby traces.
OUT
IN
on the top layer (same layer as the LM3559)
on the top layer (same layer as the LM3559)
OUT
through short wide traces will reduce
OUT
IN
FIGURE 20. Thermistor Resistive Divider Response vs Temperature
and C
and GND line and cause
OUT
should come together
IN
line.
38
4.
5.
6.
Avoid routing logic traces near the SW node so as to
avoid any capacitively coupled voltages from SW onto
any high impedance logic lines such as TX1/TORCH/
GPIO1, TX2/INT/GPIO2, HWEN, LEDI/NTC (NTC
mode), SDA, and SCL. A good approach is to insert an
inner layer GND plane underneath the SW node and
between any nearby routed traces. This creates a shield
from the electric field generated at SW.
Terminate the Flash LED cathodes directly to the GND
pin of the LM3559. If possible, route the LED returns with
a dedicated path so as to keep the high amplitude LED
currents out of the GND plane. For Flash LEDs that are
routed relatively far away from the LM3559, a good
approach is to sandwich the forward and return current
paths over the top of each other on two layers. This will
help in reducing the inductance of the LED current paths.
The NTC Thermistor is intended to have its return path
connected to the LEDs cathode. This allows the
thermistor resistive divider voltage (V
comparators threshold as V
thermistor to LED cathode junction should be connected
as close as possible in order to reduce the thermal
impedance between the LED and the thermistor. The
draw back is that the thermistor's return will see the
switching currents from the LM3559's boost converter.
Because of this, it is necessary to have a filter capacitor
at the NTC pin which terminates close to the GND of the
LM3559 (see CBYP in ).
30102834
NTC
is falling. Additionally, the
NTC
) to trip the