ELM620BA 1.4MHz
high efficiency synchronous PWM step up DC/DC converter
■Application notes
1) PCB layout guidelines
The high speed operation of ELM620BA demands careful attention to board layout, and in order to get adver-
tised performance, a well-planned layout is required. Figure-1 is an example which shows the recommended
component placement with optional Schottky diode. A large ground pin copper area will help to lower the chip
temperature. A multilayer board with a separate ground plane is ideal, but not absolutely necessary.
Fig-1
1
2
3
6
5
4
VIN
SW
Vin
GND VOUT
FB EN
EN
Vout
Figure 1: Recommended component placement for single layer board with optional Schottky diode. Traces car-
rying high current are direct. Trace area at FB pin is small. Lead length to battery is short.
2) Inductor selection
ELM620BA can utilize small surface mount and chip inductors due to its fast 1.4MHz switching frequency.
Typically, a 2.2μH inductor is recommended for most applications; larger values of inductance will allow great-
er output current capability by reducing the inductor ripple current. Increasing the inductance above 10μH will
increase size while providing little improvement in output current capability.
Vin×D
2×f×L
Iout(max) = η × (Ip −
) × (1 − D)
where:
η = estimated efficiency
Vin = input (battery) voltage
f = switching frequency (1.4MHz typical)
Ip = peak current limit value (0.7A)
D = steady-state duty ratio = (Vout − Vin) / Vout
L = inductance value
The inductor current ripple is typically set for 20% to 40% of the maximum inductor current (IP). High fre-
quency ferrite core inductor materials reduce frequency dependent power losses compared to cheaper powdered
iron types. 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. Molded chokes and some chip induc-
tors usually do not have enough core to support the peak inductor currents of 950mA seen on ELM620BA. To
minimize radiated noise, ELM recommends using a toroid, pot core or shielded bobbin inductor. See Table for
some suggested components and suppliers.
Table : Recommended inductors.
L
(μH)
2.2
Max. DCR
(mΩ)
75
Max. DC current
Size: W × L × H
(mm3)
3.8×3.8×1.8
4.0×4.0×1.8
Part
Vendor
(A)
1.2
1.2
CDRH3D16
CDH3B16
Sumida
Ceaiya
2.2
70
Rev.1.0
10 - 5
ELM-TECH [ ELM Technology Corporation ]
