LM36010 Datasheet, PDF (33/37 Pages) Texas Instruments – Synchronous-Boost, Single-LED Flash Driver With 1.5-A High-Side Current Source

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LM36010
SNVSAN4A – APRIL 2017 – REVISED JULY 2017
9 Power Supply Recommendations
The LM36010 is designed to operate from an input voltage supply range between 2.5 V and 5.5 V. This input
supply must be well regulated and capable to supply the required input current. If the input supply is located far
from the LM36010 additional bulk capacitance may be required in addition to the ceramic bypass capacitors.
10 Layout
10.1 Layout Guidelines
The high switching frequency and large switching currents of the LM36010 make the choice of layout important.
The following steps are to 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. Place C_IN on the top layer (same layer as the LM36010) and as close as possible to the device. The input
capacitor conducts the driver currents during the low-side MOSFET turnon and turnoff and can detect current
spikes over 1 A in amplitude. Connecting the input capacitor through short, wide traces to both the IN and
GND pins reduces the inductive voltage spikes that occur during switching which can corrupt the V_IN line.
2. Place C_OUT on the top layer (same layer as the LM36010) and as close as possible to the OUT and GND
pins. The returns for both C_IN and C_OUT must come together at one point, as close as possible to the GND
pin. Connecting C_OUT through short, wide traces reduce the series inductance on the OUT and GND pins that
can corrupt the V_OUT and GND lines and cause excessive noise in the device and surrounding circuitry.
3. Connect the inductor on the top layer close to the SW pin. There must 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 must be small so as to reduce the capacitive coupling of the high dV/dT present at SW that can couple
into nearby traces.
4. 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 STROBE, 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.
5. Terminate the flash LED cathode directly to the GND pin of the LM36010. If possible, route the LED return
with a dedicated path so as to keep the high amplitude LED current out of the GND plane. For a flash LED
that is routed relatively far away from the LM36010, a good approach is to sandwich the forward and return
current paths over the top of each other on two layers. This helps reduce the inductance of the LED current
path.
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