Preliminary
EUP2520
Inductor Selection
Using VSUB in Current Mode Configuration
The inductor used with EUP2520 must have a
saturation current greater than the device switch peak
current limit. Choosing inductors with low DCR
decreases power losses and increases efficiency. A 10
If Vsub is used to drive a string of LEDs, instead of
using figure 4 configuration (voltage mode). The LEDs
can be arranged in current mode configuration to control
load current.
µ
H inductor is optimal for the applications. If a
smaller inductor is used, the larger the inductor ripple
current. Care must be taken to select the inductor such
that the peak current rating of the inductor accounts for
maximum load current for the operating condition. It
is best to select an inductor with a peak current rating
of the maximum switch peak current of the device.
The following equation is useful for determining the
2× I
×
V − V
− V
DIODE
OUT
O
IN _ MIN
_ MAX
Lmin =
2
I
×f max
Peak
inductor value for a given application condition. Where
IOUT_MAX=maximum output load current, VOUT= output
voltage, VIN_VIN= minimum input voltage, VDIODE
diode forward voltage, IPEAK= Peak Current and f
= maximum switch frequency.
=
max
Figure 6.
Diode Selection
Main & Sub Enable
To maintain high efficiency, the average current rating
The EUP2520 has two independent enable pins to
control the main and sub displays. A high on the Main
Enable signal will enable the main display. While a
high on the Sub Enable pin will enable the sub
display. When Main Display enable, PWM pin must
be High or PWM Signal. Both Main & Sub enable
pins should not be ON at the same time during normal
operation. If for any reason, the main and Sub enable
are high, the main display will enable by default and
the sub display will disable by default. The following
truth table summarize the logic state.
of the schottky diode should be larger than the peak
inductor current. Schottky diodes with a low forward
drop and fast switching speeds are ideal for increasing
efficiency in portable applications. Choose a reverse
breakdown of the schottky diode larger than the
output voltage. Some recommended diodes are
MBR0530T1
from
ON
semiconductor
and
CMMSHI-40 from Central Semiconductor.
Capacitor Selection
Choose low ESR capacitors for the output to minimize
output voltage ripple. Ceramic capacitors such as X5R
and X7R are recommended for use as input and output
filiters. These capacitors provide an ideal balance
between small size, cost, reliability and performance.
Do not use Y5V ceramic capacitors as hey have poor
dielectric performance over temperature and poor
voltage characteristic for a given value. For most
applications, a 1 µF ceramic output capacitor is
sufficient for the main-display. A minimum of 4.7µF
output capacitor is recommended for VSUB output.
Larger output capacitor can be used to reduce ripple
voltage. The EUP2520 has a maximum OVP of 24.2V,
Table 1.
MAIN_EN SUB_EN PWM
MAIN
OFF
ON
SUB
OFF
OFF
OFF
0
1
0
0
X
1
X
1
0
OFF
PWM
PWM
X
OFF
ON
DIMMING
OFF
a
25V minimum rated capacitor voltage is
recommended for the application to ensure proper
biasing.
Local bypassing for the input is needed on EUP2520.
Multi-layer ceramic capacitors with low ESR are a
good choice for this as well. A 10
µF capacitor is
sufficient for most applications. Using larger
DS2520 Ver0.1 May. 2007
11
EUTECH [ EUTECH MICROELECTRONICS INC ]
