FEATURES
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LTC3633
Dual Channel 3A, 15V
Monolithic Synchronous
Step-Down Regulator
DESCRIPTION
The LTC
®
3633 is a high efficiency, dual-channel monolithic
synchronous buck regulator using a controlled on-time,
current mode architecture, with phase lockable switching
frequency. The two channels can run 180° out of phase,
which relaxes the requirements for input and output ca-
pacitance. The operating supply voltage range is from 3.6V
to 15V, making it suitable for dual cell lithium-ion batteries
as well as point of load power supply applications from
a 12V or 5V supply.
The operating frequency is programmable and synchroniz-
able from 500kHz to 4MHz with an external resistor. The
high frequency capability allows the use of small surface
mount inductors and capacitors. The unique constant
frequency/controlled on-time architecture is ideal for
high step-down ratio applications that operate at high
frequency while demanding fast transient response. An
internal phase lock loop servos the on-time of the internal
one-shot timer to match the frequency of the internal clock
or an applied external clock.
The LTC3633 can select between forced continuous mode
and high efficiency Burst Mode operation.
L,
LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks
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.
3.6V to 15V Input Voltage Range
3A Output Current per Channel
Up to 95% Efficiency
Low Duty Cycle Operation: 5% at 2.25MHz
Selectable 0°/180° Phase Shift Between Channels
Adjustable Switching Frequency: 500kHz to 4MHz
External Frequency Synchronization
Current Mode Operation for Excellent Line and
Load Transient Response
0.6V Reference Allows Low Output Voltages
User Selectable Burst Mode
®
Operation or Forced
Continuous Operation
Output Voltage Tracking and Soft-Start Capability
Short-Circuit Protected
Overvoltage Input and Overtemperature Protection
Low Power 2.5V Linear Regulator Output
Power Good Status Outputs
Available in (4mm
×
5mm) QFN-28 and 28-Lead
TSSOP Packages
APPLICATIONS
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Distributed Power Systems
Battery Powered Instruments
Point of Load Power Supplies
TYPICAL APPLICATION
V
IN
3.6V TO 15V
47μF
x2
RUN1
RUN2
V
IN2
V
IN1
INTV
CC
ITH1
ITH2
RT
EFFICIENCY (%)
100
2.2μF
90
80
70
60
50
40
30
0.1μF
SW2
V
ON2
V
FB2
73.2k
22μF
10k
SW1
V
ON1
V
FB1
10k
45.3k
22μF
3633 TA01a
Efficiency vs Load Current
Burst Mode
OPERATION
LTC3633
TRACKSS2
PGOOD2
BOOST2
V
OUT2
5V AT 3A
1.5μH
0.1μF
MODE/SYNC
PHMODE
V2P5
TRACKSS1
PGOOD1
BOOST1
1μH
V
OUT1
3.3V AT 3A
20
10
0
1
V
IN
= 12V
10
V
OUT
= 5V
V
OUT
= 3.3V
1000
100
LOAD CURRENT (mA)
10000
3633 TA01b
SGND PGND
3633f
1
LTC3633
ABSOLUTE MAXIMUM RATINGS
(Note 1)
V
IN1
, V
IN2
................................................... –0.3V to 16V
V
IN1
, V
IN2
Transient ...................................................18V
PGOOD1, PGOOD2, V
ON1
, V
ON2
................. –0.3V to 16V
BOOST1, BOOST2 ................................... –0.3V to 19.6V
BOOST1-SW1, BOOST2-SW2 ................... –0.3V to 3.6V
V2P5, INTV
CC
, TRACKSS1, TRACKSS2 ...... –0.3V to 3.6V
ITH1, ITH2, REXT, MODE/SYNC .... –0.3V to INTV
CC
+ 0.3V
V
FB1
, V
FB2
, PHMODE. .................. –0.3V to INTV
CC
+ 0.3V
RUN1, RUN2 .................................... –0.3V to V
IN
+ 0.3V
SW1, SW2 ....................................... –0.3V to V
IN
+ 0.3V
SW Source and Sink Current (DC) (Note 2) ................3A
Operating Junction Temperature Range
(Note 3).................................................. –40°C to 125°C
Storage Temperature Range................... –65°C to 125°C
PIN CONFIGURATION
TOP VIEW
TRACKSS1
ITH1
V
ON1
ITH1
SW1
SW1
TRACKSS1
V
FB1
22 V
IN1
21 V
IN1
20 BOOST1
29
PGND
19 INTV
CC
18 V2P5
17 BOOST2
16 V
IN2
15 V
IN2
9 10 11 12 13 14
ITH2
V
ON2
SW2
TRACKSS2
SW2
V
FB2
PGOOD1
PHMODE
RUN1
MODE/SYNC
RT
RUN2
1
2
3
4
5
6
7
8
9
29
PGND
TOP VIEW
28 V
ON1
27 SW1
26 SW1
25 V
IN1
24 V
IN1
23 BOOST1
22 INTV
CC
21 V2P5
20 BOOST2
19 V
IN2
18 V
IN2
17 SW2
16 SW2
15 V
ON2
28 27 26 25 24 23
PGOOD1 1
PHMODE 2
RUN1 3
MODE/SYNC 4
RT 5
RUN2 6
SGND 7
PGOOD2 8
V
FB1
SGND 10
PGOOD2 11
V
FB2
12
TRACKSS2 13
ITH2 14
UFD PACKAGE
28-LEAD (4mm
×
5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 43°C/W
EXPOSED PAD (PIN 29) IS PGND, MUST BE SOLDERED TO PCB
FE PACKAGE
28-LEAD PLASTIC TSSOP
T
JMAX
= 125°C,
θ
JA
= 25°C/W
EXPOSED PAD (PIN 29) IS PGND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3633EUFD#PBF
LTC3633IUFD#PBF
LTC3633EFE#PBF
LTC3633IFE#PBF
TAPE AND REEL
LTC3633EUFD#TRPBF
LTC3633IUFD#TRPBF
LTC3633EFE#TRPBF
LTC3633IFE#TRPBF
PART MARKING*
3633
3633
LTC3633FE
LTC3633FE
PACKAGE DESCRIPTION
28-Lead (4mm
×
5mm) Plastic QFN
28-Lead (4mm
×
5mm) Plastic QFN
28-Lead Plastic TSSOP
28-Lead Plastic TSSOP
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
–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.
Consult LTC Marketing for information on non-standard lead based finish parts.
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/
3633f
2
LTC3633
ELECTRICAL CHARACTERISTICS
SYMBOL
V
IN
I
Q
PARAMETER
Supply Range
Input DC Supply Current (V
IN1
+ V
IN2
)
Both Channels Active (Note 5)
Sleep Current
Shutdown
Feedback Reference Voltage
Reference Voltage Line Regulation
Output Voltage Load Regulation
Feedback Pin Input Current
Error Amplifier Transconductance
Minimum On Time
Minimum Off Time
Oscillator Frequency
ITH = 1.2V
V
ON
= 1V, V
IN
= 4V
V
IN
= 6V
V
RT
= INTV
CC
RT = 160k
RT = 80k
1.4
1.7
3.4
2.6
2.6
1.8
20
40
2
2
4
3.5
3.5
130
65
130
65
V
IN
= 15V, V
RUN
= 0V
V
IN
Rising
V
IN
Falling
3.6V < V
IN
< 15V, 0mA Load
0mA to 50mA Load, V
IN
= 4V to 15V
l
l
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
J
= 25°C. V
IN
= 12V, INTV
CC
= 3.3V, unless otherwise noted.
CONDITIONS
l
MIN
3.6
TYP
MAX
15
UNITS
V
mA
μA
μA
MODE = 0V
MODE = INTV
CC
, V
FB1
, V
FB2
> 0.6
RUN = 0V
l
1.3
500
13
0.594
0.6
0.02
0.05
±30
0.606
V
FB
ΔV
LINE_REG
ΔV
LOAD_REG
I
FB
g
m(EA)
t
ON
t
OFF
f
OSC
V
%/V
%
nA
mS
ns
V
IN
= 3.6V to 15V
ITH = 0.8V to 1.6V
60
2.6
2.3
4.6
4.5
4.5
ns
MHz
MHz
MHz
A
A
mΩ
mΩ
mΩ
mΩ
I
LIM
Valley Switch Current Limit
Channel 1 (3A)
Channel 2 (3A)
Channel 1
Top Switch On-Resistance
Bottom Switch On-Resistance
Channel 2
Top Switch On-Resistance
Bottom Switch On-Resistance
Switch Leakage Current
V
IN
Overvoltage Lockout Threshold
INTV
CC
Voltage
INTV
CC
Load Regulation
RUN Threshold Rising
RUN Threshold Falling
RUN Leakage Current
V2P5 Voltage
PGOOD Good-to-Bad Threshold
PGOOD Bad-to-Good Threshold
V
IN
= 15V
I
LOAD
= 0mA to 10mA
V
FB
Rising
V
FB
Falling
V
FB
Falling
V
FB
Rising
10mA Load
l
R
DS(ON)
I
SW(LKG)
V
VIN-OV
0.01
16.8
15.8
3.1
1.18
0.98
2.46
17.5
16.5
3.3
0.7
1.22
1.01
0
2.5
8
–8
–3
3
20
–5
5
15
40
400
±1
18
17
3.5
1.26
1.04
±3
2.54
10
–10
μA
V
V
V
%
V
V
μA
V
%
%
%
%
Ω
μs
R
PGOOD
t
PGOOD
t
SS
I
TRACKSS
V
PHMODE
PGOOD Pull-Down Resistance
Power Good Filter Time
Internal Soft-Start Time
V
FB
During Tracking
TRACKSS Pull-Up Current
PHMODE Threshold Voltage
700
0.315
μs
V
μA
V
V
TRACKSS = 0.3V
PHMODE V
IH
PHMODE V
IL
0.28
1
0.3
1.4
0.3
3633f
3
LTC3633
ELECTRICAL CHARACTERISTICS
SYMBOL
V
MODE/SYNC
PARAMETER
MODE/SYNC Threshold Voltage
SYNC Threshold Voltage
I
MODE
MODE/SYNC Input Current
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
J
= 25°C. V
IN
= 12V, INTV
CC
= 3.3V, unless otherwise noted.
CONDITIONS
MODE V
IH
MODE V
IL
SYNC V
IH
MODE = 0V
MODE = INTV
CC
MIN
1
0.4
0.95
1.5
–1.5
TYP
MAX
UNITS
V
V
V
μA
μA
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:
Guaranteed by long term current density limitations.
Note 3:
The LTC3633E is guaranteed to meet specified performance from
0°C to 85°C. Specifications over the –40°C to 125°C operating junction
temperature range are assured by design, characterization and correlation
with statistical process controls. The LTC3633I is guaranteed to meet
specifications over the full –40°C to 125°C operating junction
temperature range
Note 4:
This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability.
Note 5:
Dynamic supply current is higher due to the internal gate charge
being delivered at the switching frequency.
3633f
4
LTC3633
TYPICAL PERFORMANCE CHARACTERISTICS
otherwise noted.
Efficiency vs Load Current
Burst Mode Operation
100
90
80
EFFICIENCY (%)
EFFICIENCY (%)
70
60
50
40
30
20
10
0
1
10
1000
100
LOAD CURRENT (mA)
10000
3633 G01
T
J
= 25°C, V
IN
= 12V, f
SW
= 1MHz, L = 1μH unless
Efficiency vs Load Current
Forced Continuous Mode
Operation
100
90
80
EFFICIENCY (%)
70
60
50
40
30
V
OUT
= 1.8V
100
90
80
70
60
50
40
30
V
IN
= 4V
V
IN
= 8V
V
IN
= 12V
1
10
1000
100
LOAD CURRENT (mA)
10000
3633 G02
Efficiency vs Load Current
Burst Mode
OPERATION
FORCED
CONTINUOUS
OPERATION
V
OUT
= 1.8V
V
IN
= 4V
V
IN
= 8V
V
IN
= 12V
20
10
0
20
10
0
1
10
V
OUT
= 5V
V
OUT
= 3.3V
1000
100
LOAD CURRENT (mA)
10000
3633 G03
Efficiency vs Load Current
100
90
80
EFFICIENCY (%)
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.1
1
V
IN
= 4V
V
IN
= 8V
V
IN
= 12V
V
IN
= 15V
10
1000
100
LOAD CURRENT (mA)
10000
3633 G04
Efficiency vs Input Voltage
Burst Mode Operation
100
95
90
85
80
75
70
65
60
4
6
I
LOAD
= 10mA
I
LOAD
= 100mA
I
LOAD
= 1A
I
LOAD
= 3A
10
12
8
INPUT VOLTAGE (V)
14
16
3633 G05
Reference Voltage
vs Temperature
0.605
0.603
V
FB
(V)
0.601
0.599
0.597
0.595
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3633 G06
Load Regulation
1.6
Burst Mode OPERATION
FORCED CONTINUOUS
FREQUENCY VARIATION (%)
10
8
6
Oscillator Frequency
vs Temperature
2.6
2.4
FREQUENCY (MHz)
2.2
2.0
1.8
1.6
Oscillator Internal Set Frequency
vs Temperature
R
T
= INTV
CC
1.2
ΔV
OUT
/V
OUT
(%)
4
2
0
–2
–4
–6
–8
0.8
0.4
0.0
–0.4
0
0.5
1
1.5
I
LOAD
(A)
2
2.5
3
3633 G07
–10
–50
–25
0
50
75
25
TEMPERATURE (°C)
100
125
1.4
–50
–25
0
50
75
25
TEMPERATURE (°C)
100
125
3633 G08
3633 G09
3633f
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