step-down DC/DC converter that can deliver up to 10A
output current from a 4.5V to 32V (36V maximum) input
supply. It uses a constant on-time valley current mode
control architecture to deliver very low duty cycle opera-
tion at high frequency with excellent transient response.
The operating frequency is selected by an external resistor
and is compensated for variations in V
IN
and V
OUT
.
The LTC3611 can be configured for discontinuous or
forced continuous operation at light load. Forced continu-
ous operation reduces noise and RF interference while
discontinuous mode provides high efficiency by reducing
switching losses at light loads.
Fault protection is provided by internal foldback current
limiting, an output overvoltage comparator and an optional
short-circuit shutdown timer. Soft-start capability for sup-
ply sequencing is accomplished using an external timing
capacitor. The regulator current limit is user programmable.
A power good output voltage monitor indicates when
the output is in regulation. The LTC3611 is available in a
compact 9mm × 9mm QFN package.
10A Output Current
Wide V
IN
Range = 4.5V to 32V (36V Maximum)
Internal N-Channel MOSFETs
True Current Mode Control
Optimized for High Step-Down Ratios
t
0N(MIN)
≤ 100ns
Extremely Fast Transient Response
Stable with Ceramic C
OUT
±1% 0.6V Voltage Reference
Power Good Output Voltage Monitor
Adjustable On-Time/Switching Frequency (>1MHz)
Adjustable Current Limit
Programmable Soft-Start
Output Overvoltage Protection
Optional Short-Circuit Shutdown Timer
Low Shutdown I
Q
: 15μA
Available in a 9mm × 9mm 64-Pin QFN Package
APPLICATIONS
n
n
Point of Load Regulation
Distributed Power Systems
L,
LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners. Protected by U.S. Patents including
5481178, 6100678, 6580258, 5847554, 6304066.
TYPICAL APPLICATION
High Efficiency Step-Down Converter
0.1μF V
OUT
182k
V
ON
RUN/SS
100pF
LTC3611
1μH
SW
680pF
12.5k
I
TH
SGND
39.2k
INTV
CC
11k
V
RNG
PGOOD
EXTV
CC
PGND
V
FB
3611 TA01a
Efficiency and Power Loss vs
Load Current
100
90
V
IN
4.5V TO 32V
EFFICIENCY (%)
80
70
60
50
40
30
20
POWER LOSS,
V
IN
= 25V
1
0.1
1
LOAD CURRENT (A)
10
3611 TA01b
V
OUT
= 2.5V
V
IN
= 5V
V
IN
= 25V
10000
I
ON
V
IN
10μF
×3
1000
POWER LOSS (mW)
0.22μF
BOOST
INTV
CC
FCB
4.7μF
100μF
×2
V
OUT
2.5V
10A
POWER LOSS,
V
IN
= 5V
100
10
30.1k
10
0
0.01
9.5k
3611fb
1
LTC3611
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
54 INTV
CC
53 INTV
CC
64 PGND
63 PGND
62 PGND
61 PGND
60 PGND
59 PGND
58 PGND
57 PGND
56 PGND
50 SGND
49 SGND
52 SV
IN
51 SV
IN
55 SW
Input Supply Voltage (V
IN
, I
ON
) .................. 36V to –0.3V
Boosted Topside Driver Supply Voltage
(BOOST) ................................................ 42V to –0.3V
SW Voltage ............................................... 36V to –5V
INTV
CC
, EXTV
CC
, (BOOST – SW), RUN/SS,
PGOOD Voltages ...................................... 7V to –0.3V
FCB, V
ON
, V
RNG
Voltages............ INTV
CC
+ 0.3V to –0.3V
I
TH
, V
FB
Voltages ....................................... 2.7V to –0.3V
Operating Temperature Range
(Note 4) ............................................. –40°C to 125°C
Junction Temperature (Note 2) ............................. 125°C
Storage Temperature Range...................–55°C to 125°C
PGND 1
PGND 2
PGND 3
SW 4
SW 5
SW 6
SW 7
SW 8
SW 9
SW 10
SW 11
PV
IN
12
PV
IN
13
PV
IN
14
PV
IN
15
PV
IN
16
65
PGND
48 SGND
47 SGND
46 SGND
45 SGND
44 EXTV
CC
43 V
FB
66
SW
42 SGND
41 I
ON
40 SGND
39 FCB
68
SGND
38 I
TH
37 V
RNG
36 PGOOD
35 V
ON
34 SGND
33 SGND
67
PV
IN
SGND 28
BOOST 29
RUN/SS 30
SGND 31
WP PACKAGE
64-LEAD (9mm × 9mm) QFN MULTIPAD
T
JMAX
= 125°C,
θ
JA
= 28°C/W
ORDER INFORMATION
LEAD FREE FINISH
LTC3611EWP#PBF
LTC3611IWP#PBF
LEAD BASED FINISH
LTC3611EWP
LTC3611IWP
TAPE AND REEL
LTC3611EWP#TRPBF
LTC3611IWP#TRPBF
TAPE AND REEL
LTC3611EWP#TR
LTC3611IWP#TR
PART MARKING*
LTC3611WP
LTC3611WP
PART MARKING*
LTC3611WP
LTC3611WP
PACKAGE DESCRIPTION
64-Lead (9mm
×
9mm) Plastic QFN
64-Lead (9mm
×
9mm) Plastic QFN
PACKAGE DESCRIPTION
64-Lead (9mm
×
9mm) Plastic QFN
64-Lead (9mm
×
9mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
SGND 32
PV
IN
17
PV
IN
18
PV
IN
19
PV
IN
20
PV
IN
21
PV
IN
22
PV
IN
23
PV
IN
24
PV
IN
25
SW 26
NC 27
3611fb
2
LTC3611
ELECTRICAL CHARACTERISTICS
SYMBOL
Main Control Loop
V
IN
I
Q
Operating Input Voltage Range
Input DC Supply Current
Normal
Shutdown Supply Current
Feedback Reference Voltage
LTC3611E
LTC3611I
Feedback Voltage Line Regulation
Feedback Voltage Load Regulation
Feedback Input Current
Error Amplifier Transconductance
Forced Continuous Threshold
Forced Continuous Pin Current
On-Time
Minimum On-Time
Minimum Off-Time
Maximum Valley Current
Maximum Reverse Valley Current
Output Overvoltage Fault Threshold
RUN Pin Start Threshold
RUN Pin Latchoff Enable Threshold
RUN Pin Latchoff Threshold
Soft-Start Charge Current
Soft-Start Discharge Current
Undervoltage Lockout
Undervoltage Lockout Release
Top Switch On-Resistance
Bottom Switch On-Resistance
RUN/SS Pin Rising
RUN/SS Pin Falling
V
RUN/SS
= 0V
V
RUN/SS
= 4.5V, V
FB
= 0V
V
IN
Falling
V
IN
Rising
l
l
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V unless otherwise noted.
PARAMETER
CONDITIONS
MIN
4.5
900
15
I
TH
= 1.2V (Note 3)
–40°C ≤ T
J
≤ 85°C
–40°C ≤ T
J
≤ 125°C
V
IN
= 4V to 30V, I
TH
= 1.2V (Note 3)
I
TH
= 0.5V to 1.9V (Note 3)
V
FB
= 0.6V
I
TH
= 1.2V (Note 3)
V
FCB
= 0.6V
I
ON
= 60μA, V
ON
= 1.5V
I
ON
= 60μA, V
ON
= 0V
I
ON
= 180μA, V
ON
= 0V
I
ON
= 30μA, V
ON
= 1.5V
V
RNG
= 0V, V
FB
= 0.56V, FCB = 0V
V
RNG
= 1V, V
FB
= 0.56V, FCB = 0V
V
RNG
= 0V, V
FB
= 0.64V, FCB = 0V
V
RNG
= 1V, V
FB
= 0.64V, FCB = 0V
l
l
l
l
TYP
MAX
32
2000
30
0.606
0.610
–0.3
±50
2
0.66
–2
310
100
500
UNITS
V
μA
μA
V
V
%/V
%
nA
mS
V
μA
ns
ns
ns
ns
A
A
V
FB
l
0.594
0.590
0.600
0.600
0.002
–0.05
–5
ΔV
FB(LINEREG)
ΔV
FB(LOADREG)
I
FB
g
m(EA)
V
FCB
I
FCB
t
ON
t
ON(MIN)
t
OFF(MIN)
I
VALLEY(MAX)
I
VALLEY(MIN)
ΔV
FB(OV)
V
RUN/SS(ON)
V
RUN/SS(LE)
V
RUN/SS(LT)
I
RUN/SS(C)
I
RUN/SS(D)
V
IN(UVLO)
V
IN(UVLOR)
R
DS(ON)
1.4
0.54
190
1.7
0.6
–1
250
120
60
290
6
8
–4
–6
7
0.8
10
15
–6
–8
10
1.5
4
3.5
–8
–10
13
2
4.5
4.2
–3
3
3.9
4
22
14
A
A
%
V
V
V
μA
μA
V
V
mΩ
mΩ
–0.5
0.8
–1.2
1.8
3.4
3.5
15
9
3611fb
3
LTC3611
ELECTRICAL CHARACTERISTICS
SYMBOL
V
INTVCC
ΔV
LDO(LOADREG)
V
EXTVCC
ΔV
EXTVCC
ΔV
EXTVCC(HYS)
PGOOD Output
ΔV
FBH
ΔV
FBL
ΔV
FB(HYS)
V
PGL
PGOOD Upper Threshold
PGOOD Lower Threshold
PGOOD Hysteresis
PGOOD Low Voltage
V
FB
Rising
V
FB
Falling
V
FB
Returning
I
PGOOD
= 5mA
7
–7
10
–10
1
0.15
13
–13
2.5
0.4
%
%
%
V
PARAMETER
Internal V
CC
Voltage
Internal V
CC
Load Regulation
EXTV
CC
Switchover Voltage
EXTV
CC
Switch Drop Voltage
EXTV
CC
Switchover Hysteresis
Internal V
CC
Regulator
6V < V
IN
< 30V, V
EXTVCC
= 4V
I
CC
= 0mA to 20mA, V
EXTVCC
= 4V
I
CC
= 20mA, V
EXTVCC
Rising
I
CC
= 20mA, V
EXTVCC
= 5V
l
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V unless otherwise noted.
CONDITIONS
MIN
4.7
4.5
TYP
5
–0.1
4.7
150
500
300
MAX
5.6
±2
UNITS
V
%
V
m/V
m/V
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
as follows:
T
J
= T
A
+ (P
D
• 28°C/W) (θ
JA
is simulated per JESD51-7 high
effective thermal conductivity test board)
θ
JC
= 1°C/W (θ
JC
is simulated when heatsink is applied at the
bottom of the package)
Note 3:
The LTC3611 is tested in a feedback loop that adjusts V
FB
to
achieve a specified error amplifier output voltage (I
TH
). The specification at
85°C is not tested in production. This specification is assured by design,
characterization, and correlation to testing at 125°C.
Note 4:
The LTC3611E is guaranteed to meet performance specifications
from 0°C to 125°C. Specifications over the –40°C to 125°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls. The LTC3611I is guaranteed over the full
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