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 to
relax the requirements for input and output capacitance. The
operating supply voltage range is from 3.6V to 20V, making
it suitable for lithium-ion battery stacks as well as point of
load power supply applications from a 12V or 5V supply.
The operating frequency is programmable from 500kHz to
4MHz with an external resistor and may be synchronized
to an external clock signal. The high frequency capabil-
ity 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 applica-
tions that operate at high frequency while demanding fast
transient response. An internal phase locked 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 LTC3633A can select between forced continuous mode
and high efficiency Burst Mode operation. The LTC3633A
and LTC3633A-1 differ in their output voltage sense range
(refer to Table 1 in the Operation section for a description
of the entire LTC3633A product family).
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.
n
n
n
n
n
n
n
n
n
3.6V to 20V 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 Mode Operation
Output Voltage Tracking and Soft-Start Capability
Short-Circuit Protected
Overvoltage Input and Overtemperature Protection
Power Good Status Outputs
LTC3633: 16V Absolute Maximum V
IN
LTC3633A: 20V Absolute Maximum V
IN
, Pin Compatible
with LTC3633
Low Profile (4mm
×
5mm) QFN-28 and 28-Lead
TSSOP Packages
APPLICATIONS
n
n
n
Distributed Power Systems
Battery Powered Instruments
Point of Load Power Supplies
TYPICAL APPLICATION
V
IN
6V TO 20V
47µF
x2
RUN1
RUN2
INTV
CC
ITH1
ITH2
LTC3633A
RT
MODE/SYNC
PHMODE
V2P5
TRACKSS2
TRACKSS1
PGOOD2
PGOOD1
BOOST2
BOOST1
SW2
V
ON2
V
FB2
10k
SW1
V
ON1
V
FB1
V
IN2
V
IN1
100
90
2.2µF
EFFICIENCY (%)
80
70
60
50
40
30
20
V
OUT1
3.3V AT 3A
10
Efficiency vs Load Current
Burst Mode
OPERATION
V
OUT2
5V AT 3A
1.5µH
0.1µF
0.1µF
1µH
22µF
73.2k
SGND PGND
0
0.001
V
IN
= 12V
0.01
V
OUT
= 5V
V
OUT
= 3.3V
1
0.1
LOAD CURRENT (A)
10
3633a TA01b
10k 45.3k
22µF
3633a TA01a
3633a1fb
For more information
www.linear.com/LTC3633A
1
LTC3633A/LTC3633A-1
ABSOLUTE MAXIMUM RATINGS
(Note 1)
V
IN1
, V
IN2
................................................... –0.3V to 20V
PGOOD1, PGOOD2, V
ON1
, V
ON2
................. –0.3V to 18V
BOOST1, BOOST2 ...................................... –0.3V to 23V
BOOST1-SW1, BOOST2-SW2 ................... –0.3V to 3.6V
V2P5, INTV
CC
, TRACKSS1, TRACKSS2 ...... –0.3V to 3.6V
ITH1, ITH2, RT, 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
Operating Junction Temperature Range
(Notes 2, 3) ............................................ –40°C to 125°C
Storage Temperature Range................... –65°C to 150°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
V
FB2
TRACKSS2
V
ON2
ITH2
SW2
SW2
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
V
FB1
PGOOD1 1
PHMODE 2
RUN1 3
MODE/SYNC 4
RT 5
RUN2 6
SGND 7
PGOOD2 8
28 27 26 25 24 23
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
= 30°C/W
EXPOSED PAD (PIN 29) IS PGND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3633AEUFD#PBF
LTC3633AIUFD#PBF
LTC3633AEFE#PBF
LTC3633AIFE#PBF
LTC3633AEUFD-1#PBF
LTC3633AIUFD-1#PBF
LTC3633AEFE-1#PBF
LTC3633AIFE-1#PBF
TAPE AND REEL
LTC3633AEUFD#TRPBF
LTC3633AIUFD#TRPBF
LTC3633AEFE#TRPBF
LTC3633AIFE#TRPBF
LTC3633AIUFD-1#TRPBF
LTC3633AEFE-1#TRPBF
LTC3633AIFE-1#TRPBF
PART MARKING*
3633A
3633A
LTC3633AFE
LTC3633AFE
633A1
LTC3633AFE-1
LTC3633AFE-1
PACKAGE DESCRIPTION
28-Lead (4mm
×
5mm) Plastic QFN
28-Lead (4mm
×
5mm) Plastic QFN
28-Lead Plastic TSSOP
28-Lead Plastic TSSOP
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
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
LTC3633AEUFD-1#TRPBF 633A1
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/
3633a1fb
2
For more information
www.linear.com/LTC3633A
LTC3633A/LTC3633A-1
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
J
= 25°C (Note 2). V
IN1
= V
IN2
= 12V, unless otherwise noted.
SYMBOL
V
IN1
PARAMETER
Supply Range
V
IN1
Supply Range
V
IN2
Supply Range
Output Voltage Range (Note 4)
I
Q
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
= 0.6V, V
IN
= 4V
V
IN
= 6V
V
RT
= INTV
CC
RT = 162k
RT = 80.6k
1.4
1.7
3.4
2.6
1.8
20
45
2
2
4
3.5
–2
130
65
V
IN
= 20V, V
RUN
= 0V
V
IN
Rising
V
IN
Falling
3.6V < V
IN
< 20V, 0mA Load
0mA to 50mA Load, V
IN
= 4V to 20V
l
l
ELECTRICAL CHARACTERISTICS
CONDITIONS
l
l
l
MIN
3.6
3.6
1.5
0.6
1.5
TYP
MAX
20
20
20
6
12
UNITS
V
V
V
V
V
mA
µA
µA
3.6V < V
IN1
< 20V
LTC3633A, V
ON
= V
OUT
LTC3633A-1, V
ON
= V
OUT
MODE = 0V
MODE = INTV
CC
, V
FB1
, V
FB2
> 0.6
RUN1 = RUN2 = 0V
1.3
500
13
l
V
FB
∆V
LINE_REG
∆V
LOAD_REG
I
FB
g
m(EA)
t
ON
t
OFF
f
OSC
I
LIM
R
DS(ON)
I
SW(LKG)
V
VIN-OV
0.594
0.6
0.002
0.05
0.606
V
%/V
%
V
IN
= 3.6V to 20V
ITH = 0.8V to 1.6V
±30
nA
mS
ns
ns
2.6
2.3
4.6
4.5
MHz
MHz
MHz
A
A
mΩ
mΩ
Positive Valley Switch Current Limit
Negative Inductor Valley Current Limit
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
= 20V
I
LOAD
= 0mA to 10mA
V
FB
Rising
V
FB
Falling
V
FB
Rising
V
FB
Falling
10mA Load
l
0.01
20.3
3.1
1.18
0.98
2.46
22.5
21.5
3.3
1.3
1.22
1.01
0
2.5
8
–8
–3
3
20
–5
5
20
40
400
0.28
0.3
1.4
±1
22.5
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
PGOOD Pull-Down Resistance
Power Good Filter Time
Internal Soft-Start Time
V
FB
During Tracking
TRACKSS Pull-Up Current
10% to 90% Rise Time
TRACKSS = 0.3V
700
0.315
µs
V
µA
3633a1fb
For more information
www.linear.com/LTC3633A
3
LTC3633A/LTC3633A-1
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
J
= 25°C (Note 2). V
IN1
= V
IN2
= 12V, unless otherwise noted.
SYMBOL
V
PHMODE
V
MODE/SYNC
PARAMETER
PHMODE Threshold Voltage
MODE/SYNC Threshold Voltage
SYNC Threshold Voltage
I
MODE
MODE/SYNC Input Current
CONDITIONS
PHMODE V
IH
PHMODE V
IL
MODE V
IH
MODE V
IL
SYNC V
IH
MODE = 0V
MODE = INTV
CC
MIN
1
1
0.95
1.5
–1.5
TYP
MAX
0.3
0.4
UNITS
V
V
V
V
V
µA
µA
ELECTRICAL CHARACTERISTICS
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:
The LTC3633A is tested under pulsed load conditions such
that T
J
≈ T
A
. The LTC3633AE is guaranteed to meet specifications from
0°C to 85°C junction temperature. Specifications over the –40°C to
125°C operating junction temperature range are assured by design,
characterization and correlation with statistical process controls. The
LTC3633AI is guaranteed over the full –40°C to 125°C operating junction
temperature range. Note that the maximum ambient temperature
consistent with these specifications is determined by specific operating
conditions in conjunction with board layout, the rated package thermal
impedance and other environmental factors. The junction temperature
(T
J
, in °C) is calculated from the ambient temperature (T
A
, in °C) and
power dissipation (P
D
, in Watts) according to the formula:
T
J
= T
A
+ (P
D
•
θ
JA
), where
θ
JA
(in °C/W) is the package thermal
impedance.
Note 3:
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 4:
Output voltages outside the specified range are not optimized for
controlled on-time operation. Refer to the Applications Information section
for further discussions related to the output voltage range.
Note 5:
Dynamic supply current is higher due to the internal gate charge
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