LTC3605 LINER [Linear Technology], LTC3605 Datasheet - Page 12

• Manufacturer Part Number: LTC3605
• Description: 20V, 5A Synchronous Step-Down Regulator
• Manufacturer: LINER [Linear Technology]

LTC3605A
OPERATION
inductance collapses abruptly when the peak design current
is exceeded. This results in an abrupt increase in inductor
ripple current and consequent output voltage ripple. Do
not allow the core to saturate!
Table 1. Inductor Selection Table
Vishay IHLP-2525CZ-01 Series
Vishay IHLP-1616BZ-11 Series
Toko FDV0620 Series
NEC/Tokin MLC0730L Series
Cooper HCP0703 Series
TDK RLF7030 Series
Wurth Electronik WE-HC 744312 Series
12
INDUCTANCE
0.33µH
0.47µH
0.68µH
0.82µH
0.22µH
0.47µH
0.20µH
0.47µH
0.47µH
0.75µH
0.22µH
0.47µH
0.68µH
0.82µH
0.25µH
0.47µH
0.72µH
1.0µH
1.5µH
1.5µH
2.2µH
1.5µH
1µH
1µH
1µH
1µH
1µH
11.8mW
14.2mW
18.3mW
10.5mW
4.1mW
6.5mW
9.4mW
4.1mW
4.5mW
8.3mW
4.5mW
7.5mW
2.8mW
4.2mW
5.5mW
8.8mW
9.6mW
2.5mW
3.4mW
7.5mW
9.5mW
15mW
10mW
14mW
12mW
9mW
8mW
DCR
MAX CURRENT
13.5A
12.4A
16.6A
12.2A
10.6A
5.7A
6.4A
6.1A
5.4A
18A
11A
10A
12A
23A
17A
15A
13A
11A
18A
16A
12A
11A
9A
7A
9A
9A
9A
4.3mm × 4.7mm
6.9mm × 7.7mm
6.9mm × 7.3mm
6.7mm × 7mm
7mm × 7.7mm
7mm × 7.3mm
7mm × 7.7mm
DIMENSIONS
HEIGHT
2.0mm
2.0mm
3.0mm
3.0mm
3.2mm
3.8mm
3mm
Different core materials and shapes will change the size/cur-
rent and price/current relationship of an inductor. Toroid
or shielded pot cores in ferrite or permalloy materials are
small and don’t radiate much energy, but generally cost
more than powdered iron core inductors with similar
characteristics. The choice of which style inductor to use
mainly depends on the price versus size requirements
and any radiated field/EMI requirements. New designs for
surface mount inductors are available from Toko, Vishay,
NEC/Tokin, Cooper, TDK and Wurth Electronik. Refer to
Table 1 for more details.
Checking Transient Response
The OPTI-LOOP compensation allows the transient re-
sponse to be optimized for a wide range of loads and
output capacitors. The availability of the ITH pin not
only allows optimization of the control loop behavior but
also provides a DC-coupled and AC-filtered closed-loop
response test point. The DC step, rise time and settling
at this test point truly reflects the closed-loop response.
Assuming a predominantly second order system, phase
margin and/or damping factor can be estimated using the
percentage of overshoot seen at this pin.
The ITH external components shown in the circuit on the
first page of this data sheet provides an adequate starting
point for most applications. The series R-C filter sets the
dominant pole zero loop compensation. The values can
be modified slightly (from 0.5 to 2 times their suggested
values) to optimize transient response once the final PC
layout is done and the particular output capacitor type and
value have been determined. The output capacitors need to
be selected because their various types and values deter-
mine the loop feedback factor gain and phase. An output
current pulse of 20% to 100% of full load current having
a rise time of 1µs to 10µs will produce output voltage and
ITH pin waveforms that will give a sense of the overall loop
stability without breaking the feedback loop.
Switching regulators take several cycles to respond to a
step in load current. When a load step occurs, V
mediately shifts by an amount equal to DI
ESR is the effective series resistance of C
begins to charge or discharge C
error signal used by the regulator to return V
OUT
generating a feedback
LOAD
OUT
. DI
• ESR, where
OUT
LOAD
OUT
to its
also
3605af
im-