EP4001_15 Datasheet, PDF (9/10 Pages) Eorex Corporation – High Efficiency, Step-Up Converter with EXT

eorex
EP4001
Inductor Selection
The EP4001 can utilize small surface mount and chip inductors operating at 450KHz switching frequency.
The inductor current ripple is typically set for 20% to 40% of the maximum inductor current. The inductor
should have low ESR (series resistance of the windings) to reduce the I2R power losses, and must be
able to handle the peak inductor current without saturating.
Output and Input Capacitor Selection
Low ESR (equivalent series resistance) capacitors should be used to minimize the output voltage ripple.
Low ESR input capacitors reduce input switching noise and reduce the peak current drawn from the
battery. The input decoupling capacitor should be located as close as possible to the device.
Output Voltage Setting
The output voltage of the switching regulator (V_OUT) is determined by (Eq.1)
Feedback Loop Design
The value selection for R1 and R2 is based on the trade-off between quiescent current consumption and
interference immunity. Higher values for R1 and R2 will reduce the quiescent current, while Lower values
for R1 and R2 has the advantage of a better noise immunity, and is less sensitive to other interferences.
However, a resistor having a value higher than 5mΩ is not recommended. The noise immunity of the
feedback loops can be improved by using a proper value of feed forward capacitor in parallel with R1.
The value for this capacitor is between 0 to 33pF for feedback resistors of mΩ, and 10nF to 0.1μF for
feedback resistors of tens to hundreds kΩ. Be aware that such kind of “high impedance feedback Loops”
is sensitive to any interference, which require careful layout and avoid any interference.
Layout Guide
1. The power traces, which are consisted of GND trace, the SW trace and the V_IN trace should be kept
short, direct and wide.
2. Keep the switching node, SW, away from the sensitive FB node.
3. Keep the distance between pin SW and L1 as close as possible, and no more than 3-4mm.
4. Keep the distance between capacitor C3 and L1 as close as possible, no more than 3-4mm.
5. Connect the (+) plate of C_IN to V_IN as closely as possible. This capacitor provides the AC current to the
internal power MOSFETs.
6. Connect pin FB directly to the feedback resistors. The resistive divider R1/ R2 must be connected
between the (+) plate of C_OUT and ground.
7. Keep the (-) plates of C_IN and C_OUT as close as possible.
Aug. 2006
www.eorex.com
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