Recommended External Components
OUTPUT CAPACITOR: COUT
The output capacitor COUT directly affects the magnitude of
the output ripple voltage. In general, the higher the value of
COUT, the lower the output ripple magnitude. Multilayer ce-
ramic capacitors with low ESR are the best choice. Capacitor
voltage rating must be sufficient, 25V or greater is recom-
mended. Examples of suitable capacitors are: TDK
C3216X5R1E475K, Panasonic ECJ3YB1E475K and ECJ4Y-
B1E475K.
Some ceramic capacitors, especially those in small pack-
ages, exhibit a strong capacitance reduction with the in-
creased applied voltage (DC bias effect). The capacitance
value can fall below half of the nominal capacitance. Too low
output capacitance can make the boost converter unstable.
Output capacitor value reduction due to DC bias should be
less than 70% at 20V (minimum 3 µF of real capacitance re-
maining).
INPUT CAPACITOR: CIN
The input capacitor CIN directly affects the magnitude of the
input ripple voltage and to a lesser degree the VOUT ripple. A
higher value CIN will give a lower VIN ripple.
OUTPUT DIODE: DOUT
A schottky diode should be used for the output diode. To
maintain high efficiency the average current rating of the
schottky diode should be greater than the peak inductor cur-
rent (1A). Schottky diodes with a low forward drop and fast
switching speeds are ideal for increasing efficiency in portable
applications. Choose a reverse breakdown voltage of the
schottky diode significantly larger (~30V) than the output volt-
age. Do not use ordinary rectifier diodes, since slow switching
speeds and long recovery times cause the efficiency and the
load regulation to suffer. A schottky diode with low parasitic
capacitance helps in reducing EMI noise. Examples of suit-
able diodes are: Central Semiconductor CMMSH1-40 and
Infineon BAS52-02V.
EMI FILTER COMPONENTS: CSW, RSW, LSW and CHF
EMI filter (RSW, CSW and LSW ) on the SW pin may be needed
to slow down the fast switching edges and reduce ringing.
These components should be as near as possible to the SW
pin to ensure reliable operation. High frequency capacitor
(CSW) in the boost output helps in suppressing the high fre-
quency noise from the switcher. 50V or greater voltage rating
is recommended for the capacitors. The ferrite bead DC re-
sistance should be less than 0.1Ω and current rating 1A or
above. The impedance at 100 MHz should be 30 – 300Ω.
Examples of suitable types are TDK MPZ1608S101A and
Taiyo-Yuden FBMH 1608HM600-T.
INDUCTOR: L1
A 4.7 µH shielded inductor is suggested for LP5520 boost
converter. The inductor should have a saturation current rat-
ing higher than the peak current it will experience during
circuit operation (0.5 – 1.0A depending on the output current).
Less than 500 mΩ ESR is suggested for high efficiency. Open
core inductors cause flux linkage with circuit components and
interfere with the normal operation of the circuit. This should
be avoided. For high efficiency, choose an inductor with a high
frequency core material such as ferrite to reduce the core
losses. To minimize radiated noise, use a toroid, pot core or
shielded core inductor. The inductor should be connected to
the SW pin as close to the IC as possible. Examples of suit-
able inductors are: TDK VLF3010AT-4R7MR70 and Coilcraft
LPS3010-472NL.
LIST OF RECOMMENDED EXTERNAL COMPONENTS
Symbol Symbol Explanation Value Unit Type
CVDDA C between VDDA and GND 100 nF Ceramic, X7R / X5R
CVDDD C between VDDD and GND 100 nF Ceramic, X7R, X5R
CVLDO C between VLDO and GND 1 µF Ceramic, X7R / X5R
CVDDIO C between VDDIO and GND 100 nF Ceramic, X7R / X5R
COUT
C between FB and GND 2 x 4.7 µF Ceramic, X7R / X5R, tolerance
±10%, DC bias effect ~ –30% at
20V
CIN C between battery voltage and GND 10 µF Ceramic, X7R / X5R
L1L between SW and VBAT 4.7 µH Shielded, low ESR, ISAT 0.5A
D1
Rectifying Diode (Vf @ maxload) 0. 3 - 0.5 V Schottky diode, reverse voltage
30V, repetitive peak current 0.5A
CSW Optional C in EMI filter 330 pF Ceramic, X7R / X5R, 50V
RSW Optional R in EMI filter 3.9 Ω±1%
CHF Optional high frequency output C 33 - 100 pF Ceramic, X7R, X5R, 50V
LSW Ferrite bead in SW pin 30 - 300 Ω
at 100 Mhz
LEDs User Defined
www.national.com 26
LP5520