lithic 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-2 can select between forced continuous
mode and high efficiency Burst Mode operation. The
LTC3633A-2 and LTC3633A-3 differ in their output volt-
age sense range (refer to Table 1 in the Operation section
for a description of the entire LTC3633A product family).
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 Operation
Output Voltage Tracking and Soft-Start Capability
Short-Circuit Protected
Overvoltage Input and Overtemperature Protection
Power Good Status Outputs
Available in (4mm
×
5mm) QFN-28 and 28-Lead
TSSOP Packages
APPLICATIONS
n
n
n
Distributed Power Systems
Battery Powered Instruments
Point of Load Power Supplies
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.
TYPICAL APPLICATION
V
IN
6V TO 20V
47µF
x2
PV
IN2
RUN1
RUN2
PV
IN1
SV
IN
2.2µF
EFFICIENCY (%)
100
90
80
70
60
50
40
30
20
V
OUT1
3.3V AT 3A
10
INTV
CC
ITH1
LTC3633A-2
ITH2
RT
MODE/SYNC
PHMODE
TRACKSS1
PGOOD1
BOOST1
SW1
V
ON1
V
FB1
Efficiency vs Load Current
Burst Mode
OPERATION
V
OUT2
5V AT 3A
1.5µH
0.1µF
TRACKSS2
PGOOD2
BOOST2
SW2
V
ON2
V
FB2
10k
0.1µF
1µH
22µF
73.2k
SGND PGND
0
0.001
10k 45.3k
22µF
3633a23 TA01a
V
IN
= 12V
0.01
V
OUT
= 5V
V
OUT
= 3.3V
1
0.1
LOAD CURRENT (A)
10
3633a23 TA01b
3633a23fb
For more information
www.linear.com/LTC3633A-2
1
LTC3633A-2/LTC3633A-3
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PV
IN1
, PV
IN2
, SV
IN
...................................... –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
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 ............................................. –0.3V to SV
IN
+ 0.3V
RUN2 ......................................................... –0.3V to 20V
Operating Junction Temperature Range
(Notes 3, 4) ............................................ –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 PV
IN1
21 PV
IN1
20 SV
IN
29
PGND
19 BOOST1
18 INTV
CC
17 BOOST2
16 PV
IN2
15 PV
IN2
9 10 11 12 13 14
V
FB2
ITH2
V
ON2
SW2
TRACKSS2
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 PV
IN1
24 PV
IN1
23 SV
IN
22 BOOST1
21 INTV
CC
20 BOOST2
19 PV
IN2
18 PV
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
= 25°C/W
EXPOSED PAD (PIN 29) IS PGND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3633AEUFD-2#PBF
LTC3633AIUFD-2#PBF
LTC3633AEFE-2#PBF
LTC3633AIFE-2#PBF
LTC3633AEUFD-3#PBF
LTC3633AIUFD-3#PBF
LTC3633AEFE-3#PBF
LTC3633AIFE-3#PBF
TAPE AND REEL
LTC3633AIUFD-2#TRPBF
LTC3633AEFE-2#TRPBF
LTC3633AIFE-2#TRPBF
LTC3633AIUFD-3#TRPBF
LTC3633AEFE-3#TRPBF
LTC3633AIFE-3#TRPBF
PART MARKING*
633A2
LTC3633AFE-2
LTC3633AFE-2
633A3
LTC3633AFE-3
LTC3633AFE-3
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-2#TRPBF 633A2
LTC3633AEUFD-3#TRPBF 633A3
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/
3633a23fb
2
For more information
www.linear.com/LTC3633A-2
LTC3633A-2/LTC3633A-3
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
J
= 25°C (Note 2). PV
IN1
= PV
IN2
= SV
IN
= 12V unless otherwise noted.
SYMBOL
SV
IN
PARAMETER
Supply Range
PV
IN1
Supply Range
PV
IN2
Supply Range
Output Voltage Range (Note 4)
I
Q
3.6V < SV
IN
< 20V
LTC3633A-2, V
ON
= V
OUT
LTC3633A-3, V
ON
= V
OUT
CONDITIONS
l
l
l
ELECTRICAL CHARACTERISTICS
MIN
3.6
1.5
1.5
0.6
1.5
TYP
MAX
20
20
20
6
12
UNITS
V
V
V
V
V
mA
µA
µA
Input DC Supply Current (PV
IN1
+ PV
IN2
+ SV
IN
)
Both Channels Active (Note 5)
MODE = 0V
Sleep Current
MODE = INTV
CC
, V
FB1
, V
FB2
> 0.6
Shutdown
RUN1 = RUN2 = 0V
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, PV
IN
= 4V
PV
IN
= 6V
V
RT
= INTV
CC
RT = 162k
RT = 80.6k
1.4
1.7
3.4
2.6
PV
IN
= 3.6V to 20V
ITH = 0.8V to 1.6V
l
1.3
500
13
0.594
0.6
0.002
0.05
±30
1.8
20
45
2
2
4
3.5
–2
130
65
2.6
2.3
4.6
4.5
0.606
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
V
%/V
%
nA
mS
ns
ns
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
PGOOD Good-to-Bad Threshold
PGOOD Bad-to-Good Threshold
V
FB
Rising
V
FB
Falling
V
FB
Rising
V
FB
Falling
10mA Load
PV
IN
= 20V, V
RUN
= 0V
PV
IN
Rising
PV
IN
Falling
3.6V < SV
IN
< 20V, 0mA Load
0mA to 50mA Load, SV
IN
= 4V to 20V
l
l
0.01
20.3
3.1
1.18
0.98
22.5
21.5
3.3
1.3
1.22
1.01
0
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
10
–10
µA
V
V
V
%
V
V
µA
%
%
%
%
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
3633a23fb
For more information
www.linear.com/LTC3633A-2
3
LTC3633A-2/LTC3633A-3
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
J
= 25°C (Note 2). PV
IN1
= PV
IN2
= SV
IN
= 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-2/LTC3633A-3 is tested under pulsed load
conditions such that T
J
≈ T
A
. The LTC3633AE-2/ LTC3633AE-3 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-2/ LTC3633AI-3 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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FPGA/CPLD
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