Datasheet

13
LTC1530
1530fa
where L is the inductor value in µH. With proper frequency
compensation, the combination of the inductor and output
capacitor values determine the transient recovery time. In
general, a smaller value inductor improves transient
response at the expense of ripple and inductor core
saturation rating. A 2µH inductor has a 0.9A/µs rise time
in this application, resulting in a 5.5µs delay in responding
to a 5A load current step. During this 5.5µs, the difference
between the inductor current and the output current is
made up by the output capacitor. This action causes a
temporary voltage droop at the output. To minimize this
effect, the inductor value should usually be in the 1µH to
5µH range for most 5V input LTC1530 circuits. Different
combinations of input and output voltages and expected
loads may require different values.
Once the required inductor value is selected, choose the
inductor core type based on peak current and efficiency
requirements. Peak current in the inductor is equal to the
maximum output load current plus half of the peak-to-
peak inductor ripple current. Inductor ripple current is set
by the inductor’s value, the input voltage, the output
voltage and the operating frequency. If the efficiency is
high, ripple current is approximately equal to:
I
VV V
fLV
RIPPLE
IN OUT OUT
OSC O IN
=
−
()()
()()()
where
f
OSC
= LTC1530 oscillator frequency
L
O
= Inductor value
Solving this equation for a typical 5V to 2.8V application
with a 2µH inductor, ripple current is:
22 056
300 2
2
..V
kHz H
A
()()
()()
=
µ
P-P
Peak inductor current at 11.2A load:
11 2
2
2
12 2..A
A
A+=
The ripple current should generally fall between 10% and
40% of the output current. The inductor must be able to
withstand this peak current without saturating, and the
copper resistance in the winding should be kept as low as
possible to minimize resistive power loss. Note that in
APPLICATIO S I FOR ATIO
WUUU
RDS(ON) TYPICAL INPUT
AT 25
° C RATED CURRENT CAPACITANCE
θθ
θθ
θ
JC
T
JMAX
MANUFACTURER PART NO. PACKAGE ( Ω ) (A) Ciss (pF) ( ° C/W) ( ° C)
Siliconix SUD50N03-10 TO-252 0.019 15A at 25°C 3200 1.8 175
10A at 100°C
Siliconix Si4410DY SO-8 0.020 10A at 25°C 2700 — 150
8A at 75°C
ON Semiconductor MTD20N03HDL DPAK 0.035 20A at 25°C 880 1.67 150
16A at 100°C
Fairchild FDS6680 SO-8 0.01 11.5A at 25°C 2070 25 150
ON Semiconductor MTB75N03HDL* D
2
PAK 0.0075 75A at 25°C 4025 1.0 150
59A at 100°C
IR IRL3103S D
2
PAK 0.014 56A at 25°C 1600 1.8 175
40A at 100°C
IR IRLZ44 TO-220 0.028 50A at 25°C 3300 1.0 175
36A at 100°C
Fuji 2SK1388 TO-220 0.037 35A at 25°C 1750 2.08 150
Note: Please refer to the manufacturer’s data sheet for testing conditions and detailed information.
*Users must consider the power dissipation and thermal effects in the LTC1530 if driving external MOSFETs with high values of input capacitance.
Refer to the PV
CC
Supply Current vs GATE Capacitance in the Typical Performance Characteristics section.
Table 1. Recommended MOSFETs for LTC1530 Applications