UM3510_16 Datasheet, PDF (9/13 Pages) Union Semiconductor, Inc. – 1A, 2.25MHz, Synchronous Step-Down DC-DC Converter

UM3510
Application Information
Output Voltage Setting
The output voltage can be caculated according to the formula below with an internal reference
volatge V_REF typical 0.6V:
R1
V_OUT = V_REF × 1 + _R2
To minimize the current through the feedback divider network, the recommended value of R2 is
about 180kΩ. The sum of R1 and R2 should not exceed about 1MΩ to keep the network robust
against noise. An external feed forward capacitor C1 is required for optimum load transient
response. The value of C1 should be in the range between 10pF and 33pF.
Route the FB line away from noise sources, such as the inductor or the SW line.
Inductor Selection
A 1µH to 10µH inductor with DC current rating at least 25% higher than the maximum load
current is recommended for most applications. For best efficiency, the inductor DC resistance
shall be <200mΩ.
For most designs, the inductance value can be derived from the following equation:
L
=
V_OUT ×
V_IN ×
V_IN
∆I_L
− V_OUT
× f_OSC
Where ∆I_L is the inductor ripple current. Choose inductor ripple current approximately 30% of the
maximum load current, 1000mA.
The maximum inductor peak current is:
I_{L MAX}
= I_LOAD
+
∆I_L
2
The following table is a list of recommended inductors.
Dimension [mm³]
4.5×4×3.2
3×3×1.5
3×3×1.5
List of Recommended Inductors
Inductor Type
744773022
LQH3NPN2R2NM0
LPS3015
Supplier
Würth Elektronik
MURATA
Coilcraft
Input Capacitor Selection
The input capacitor reduces the surge current drawn from the input and switching noise from the
device. The input capacitor impedance at the switching frequency shall be less than the input
source impedance to prevent high frequency switching current passing to the input. Ceramic
capacitors with X5R or X7R dielectrics are highly recommended because of their low ESR and
small temperature coefficients. For most applications, a 10µF capacitor is sufficient. The input
capacitor can be increased without any limit for better input voltage filtering.
Output Capacitor Selection
The output capacitor keeps output voltage ripple small and ensures regulation loop stable. The
output capacitor impedance shall be low at the switching frequency. Ceramic capacitor with X5R
or X7R dielectrics are recommended. The output ripple ∆V_OUT is approximately:
∆V_OUT
≤
V_OUT × V_IN − V_OUT
V_IN × f_OSC × L
×
1
ESR + _{8 × fOSC × COUT}
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http://www.union-ic.com Rev.01 Jan.2016
9/13