LTC3605A
20V, 5A Synchronous
Step-Down Regulator
FEATURES
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DESCRIPTION
The LTC
®
3605A is a high efficiency, monolithic synchro-
nous buck regulator using a phase lockable controlled
on-time constant frequency, current mode architecture.
PolyPhase operation allows multiple LTC3605A regula-
tors to run out of phase while using minimal input and
output capacitance. The operating supply voltage range
is from 20V down to 4V, making it suitable for dual, triple
or quadruple lithium-ion battery inputs as well as point
of load power supply applications from a 12V or 5V rail.
The operating frequency is programmable from 800kHz to
4MHz with an external resistor. The high frequency capabil-
ity allows the use of small surface mount inductors. For
switching noise sensitive applications, it can be externally
synchronized from 800kHz to 4MHz. The PHMODE pin
allows user control of the phase of the outgoing clock
signal. The unique constant frequency/controlled on-time
architecture is ideal for high step-down ratio applications
that are operating at high frequency while demanding
fast transient response. Two internal phase-lock loops
synchronize the internal oscillator to the external clock
and also servos the regulator on-time to lock on to either
the internal clock or the external clock if it’s present.
L,
LT, LTC, LTM, PolyPhase, OPTI-LOOP Linear Technology and the Linear logo are registered
,
trademarks and Hot Swap is a trademark of Linear Technology Corporation. All other trademarks
are the property of their respective owners. Protected by U.S. Patents, including 5481178,
5847554, 6580258, 6304066, 6476589, 6774611.
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High Efficiency: Up to 96%
5A Output Current
4V to 20V V
IN
Range
Integrated Power N-Channel MOSFETs
(70mΩ Top and 35mΩ Bottom)
Adjustable Frequency 800kHz to 4MHz
PolyPhase
®
Operation (Up to 12 Phases)
Output Tracking
0.6V ±1% Reference Accuracy
Current Mode Operation for Excellent Line and Load
Transient Response
Shutdown Mode Draws Less Than 15µA Supply
Current
LTC3605: 15V Absolute Maximum V
IN
LTC3605A: 22V Absolute Maximum V
IN
The LTC3605A Is Pin Compatible with the LTC3605
Available in 24-Pin (4mm
×
4mm) QFN Package
Point of Load Power Supply
Portable Instruments
Distributed Power Systems
Battery-Powered Equipment
APPLICATIONS
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TYPICAL APPLICATION
High Efficiency 1MHz, 5A Step-Down Regulator
V
IN
4V TO 20V
22µF
×2
Efficiency and Power Loss
100
90
80
EFFICIENCY (%)
V
OUT
= 3.3V
10
PV
IN
CLKOUT
CLKIN
SV
IN
INTV
CC
70
60
50
40
30
20
10
0
0.01
0.1
1
LOAD CURRENT (A)
V
IN
= 8V
V
IN
= 12V
V
IN
= 20V
10
3605A TA01b
1
POWER LOSS (W)
2.2µF
0.1µF 1µH
11.5k
2.55k
16k
PGND
47µF
×2
BOOST
PGOOD
LTC3605A
SW
V
ON
V
IN
RUN
RT
FB
ITH
162k
V
OUT
3.3V
0.1
0.01
220pF
3605A TA01a
3605af
1
LINEAR [ LINEAR INTEGRATED SYSTEMS ]
