LT1765/LT1765-1.8/LT1765-2.5/
LT1765-3.3/LT1765-5
Monolithic 3A, 1.25MHz
Step-Down Switching Regulator
FEATURES
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DESCRIPTION
The LT
®
1765 is a 1.25MHz monolithic buck switching
regulator. A high efficiency 3A, 0.09Ω switch is included
on the die together with all the control circuitry required
to construct a high frequency, current mode switching
regulator. Current mode control provides fast transient
response and excellent loop stability.
New design techniques achieve high efficiency at high
switching frequencies over a wide operating voltage
range. A low dropout internal regulator maintains con-
sistent performance over a wide range of inputs from
24V systems to Li-Ion batteries. An operating supply
current of 1mA improves efficiency, especially at lower
output currents. Shutdown reduces quiescent current to
15μA. Maximum switch current remains constant at all
duty cycles. Synchronization allows an external logic level
signal to increase the internal oscillator into the range of
1.6MHz to 2MHz.
Full cycle-by-cycle current control and thermal shutdown
are provided. High frequency operation allows the reduc-
tion of input and output filtering components and permits
the use of chip inductors.
L,
LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
*Patent Pending
3A Switch in a Thermally Enhanced 16-Lead
TSSOP or 8-Lead SO Package
Constant 1.25MHz Switching Frequency
Wide Operating Voltage Range: 3V to 25V
High Efficiency 0.09Ω Switch
1.2V Feedback Reference Voltage
Uses Low Profile Surface Mount Components
Low Shutdown Current: 15μA
Synchronizable to 2MHz
Current Mode Loop Control
Constant Maximum Switch Current Rating at
All Duty Cycles*
Available in 8-Lead SO and 16-Lead Thermally
Enhanced TSSOP Packages
APPLICATIONS
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DSL Modems
Portable Computers
Regulated Wall Adapters
Battery-Powered Systems
Distributed Power
TYPICAL APPLICATION
5V to 3.3V Step-Down Converter
CMDSH-3
0.18μF
85
V
IN
LT1765-3.3
OFF ON
SHDN
SYNC
FB
GND
V
C
2.2nF
UPS120
4.7μF
CERAMIC
V
SW
EFFICIENCY (%)
INPUT
5V
2.2μF
CERAMIC
BOOST
1.5μH
OUTPUT
3.3V
2.5A
90
Efficiency vs Load Current
V
IN
= 10V
V
OUT
= 5V
80
75
1765 TA01
70
0
1.0
1.5
0.5
SWITCH CURRENT (A)
2.0
1765 • TAO1a
1765fd
1
LT1765/LT1765-1.8/LT1765-2.5/
LT1765-3.3/LT1765-5
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Input Voltage ........................................................... 25V
BOOST Pin Above SW ............................................. 20V
Max BOOST Pin Voltage ............................................35V
SHDN
Pin ................................................................. 25V
FB Pin Current......................................................... 1mA
SYNC Pin Current ................................................... 1mA
Operating Junction Temperature Range
(Note 2)................................................. –40°C to 125°C
Storage Temperature Range ................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec) ................ 300°C
PIN CONFIGURATION
TOP VIEW
GND
BOOST
V
IN
V
IN
SW
SW
NC
GND
1
2
3
4
5
6
7
8
17
16 GND
15 NC
14 SYNC
13 V
C
12 FB
11 SHDN
10 NC
9
GND
BOOST 1
V
IN
2
SW 3
GND 4
TOP VIEW
8 SYNC
7 V
C
6 FB
5 SHDN
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 90°C/W,
θ
JC(PIN 4)
= 30°C/W
GROUND PIN CONNECTED TO LARGE COPPER AREA
FE PACKAGE
16-LEAD PLASTIC TSSOP
θ
JA
= 45°C/W,
θ
JC(PAD)
= 10°C/W
EXPOSED PAD (PIN 17) SOLDERED TO LARGE COPPER PLANE
ORDER INFORMATION
LEAD FREE FINISH
LT1765EFE#PBF
LT1765EFE-1.8#PBF
LT1765EFE-2.5#PBF
LT1765EFE-3.3#PBF
LT1765EFE-5#PBF
LT1765ES8#PBF
LEAD BASED FINISH
LT1765EFE
LT1765EFE-1.8
LT1765EFE-2.5
LT1765EFE-3.3
LT1765EFE-5
LT1765ES8
TAPE AND REEL
LT1765EFE#TRPBF
LT1765EFE-1.8#TRPBF
LT1765EFE-2.5#TRPBF
LT1765EFE-3.3#TRPBF
LT1765EFE-5#TRPBF
LT1765ES8#TRPBF
TAPE AND REEL
LT1765EFE#TR
LT1765EFE-1.8#TR
LT1765EFE-2.5#TR
LT1765EFE-3.3#TR
LT1765EFE-5#TR
LT1765ES8#TR
PART MARKING
1765EFE
1765EFE-1.8
1765EFE-2.5
1765EFE-3.3
1765EFE-5
1765
PART MARKING
1765EFE
1765EFE-1.8
1765EFE-2.5
1765EFE-3.3
1765EFE-5
1765
PACKAGE DESCRIPTION
16-Lead Plastic TSSOP
16-Lead Plastic TSSOP
16-Lead Plastic TSSOP
16-Lead Plastic TSSOP
16-Lead Plastic TSSOP
8-Lead Plastic SO
PACKAGE DESCRIPTION
16-Lead Plastic TSSOP
16-Lead Plastic TSSOP
16-Lead Plastic TSSOP
16-Lead Plastic TSSOP
16-Lead Plastic TSSOP
8-Lead Plastic SO
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
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
Consult LTC Marketing for parts specified with wider operating temperature ranges.
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/
1765fd
2
LT1765/LT1765-1.8/LT1765-2.5/
LT1765-3.3/LT1765-5
ELECTRICAL CHARACTERISTICS
The
l
denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T
A
= 25°C.
V
IN
= 15V, V
C
= 0.8V, Boost = V
IN
+ 5V,
SHDN,
SYNC and switch open unless otherwise noted.
PARAMETER
Maximum Switch Current Limit
Oscillator Frequency
Switch On Voltage Drop
V
IN
Undervoltage Lockout
V
IN
Supply Current
Shutdown Supply Current
Feedback Voltage
V
SHDN
= 0V, V
IN
= 25V, V
SW
= 0V
3V < V
IN
< 25V, 0.4V < V
C
< 0.9V
(Note 3)
LT1765 (Adj)
LT1765-1.8
LT1765-2.5
LT1765-3.3
LT1765-5
FB Input Current
FB Input Resistance
LT1765 (Adj)
LT1765-1.8
LT1765-2.5
LT1765-3.3
LT1765-5
0.4V < V
C
< 0.9V
ΔI
VC
=
±10μA
V
FB
= V
NOM
– 17%
V
FB
= V
NOM
+ 17%
Duty Cycle = 0%
V
C
= 1.2V, I
SW
= 800mA, V
IN
= 6V
I
SW
= 3A
I
SW
= 1A (Note 4)
I
SW
= 3A (Note 4)
85
80
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CONDITIONS
3.3V < V
IN
< 25V
I = 3A
(Note 3)
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MIN
3
1.1
2.47
TYP
4
1.25
270
2.6
1
15
MAX
6
1.6
430
2.73
1.3
35
55
1.218
1.224
1.836
2.55
3.366
5.1
–0.5
21
30
39
60
1300
160
180
UNITS
A
MHz
mV
V
mA
μA
μA
V
V
V
V
V
V
μA
kΩ
kΩ
kΩ
kΩ
μMho
μA
μA
A/V
V
V
%
%
1.182
1.176
1.764
2.45
3.234
4.9
10.5
14.7
19
29
150
500
80
70
1.2
1.8
2.5
3.3
5
–0.25
15
21
27.5
42
350
850
120
110
5
0.4
0.9
90
1.8
20
70
FB Error Amp Voltage Gain
FB Error Amp Transconductance
V
C
Pin Source Current
V
C
Pin Sink Current
V
C
Pin to Switch Current Transconductance
V
C
Pin Minimum Switching Threshold
V
C
Pin 3A ISW Threshold
Maximum Switch Duty Cycle
Minimum Boost Voltage Above Switch
Boost Current
SHDN
Threshold Voltage
SHDN
Threshold Current Hysteresis
SHDN
Input Current (Shutting Down)
SYNC Threshold Voltage
SYNC Input Frequency
SYNC Pin Resistance
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2.7
30
140
1.40
10
–13
2.2
2
V
mA
mA
V
μA
μA
V
MHz
kΩ
1.27
4
–7
1.6
1.33
7
–10
1.5
SHDN
= 60mV Above Threshold
l
I
SYNC
= 1mA
20
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 LT1765E is guaranteed to meet performance specifications
from 0°C to 125°C. Specifications over the –40°C to 125°C operating
junction temperature range are assured by design, characterization and
correlation with statistical process controls.
Note 3:
Minimum input voltage is defined as the voltage where the internal
regulator enters lockout. Actual minimum input voltage to maintain a
regulated output will depend on output voltage and load current. See
Applications Information.
Note 4:
Current flows into the BOOST pin only during the on period of the
switch cycle.
1765fd
3
LT1765/LT1765-1.8/LT1765-2.5/
LT1765-3.3/LT1765-5
TYPICAL PERFORMANCE CHARACTERISTICS
FB vs Temperature (Adj)
1.220
1.215
SWITCH VOLTAGE (mV)
1.210
FB VOLTAGE (V)
1.205
1.200
1.195
1.190
1.185
1.180
–50
–25
0
25
50
75
100
125
350
300
250
200
150
100
50
0
0
TEMPERATURE (°C)
1765 G01
Switch On Voltage Drop
T
A
= 125°C
T
A
= –40°C
T
A
= 25°C
2
1
SWITCH CURRENT (A)
3
1765 G02
Oscillator Frequency
1.50
1.45
1.38
1.35
1.30
1.25
1.20
1.15
1.10
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
SHDN THRESHOLD (V)
1.40
FREQUENCY (MHz)
1.40
SHDN
Threshold vs Temperature
1.36
1.34
1.32
1.30
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
1765 G03
1765 G04
SHDN
Supply Current vs V
IN
7
SHDN = 0V
6
V
IN
CURRENT (μA)
V
IN
CURRENT (μA)
5
4
3
2
1
0
0
5
10
15
V
IN
(V)
20
25
30
1765 G05
SHDN
I
P
Current vs Temperature
7
SHDN = 0V
6
5
4
3
2
1
0
0
5
10
15
V
IN
(V)
20
25
30
1765 G05
1765fd
4
LT1765/LT1765-1.8/LT1765-2.5/
LT1765-3.3/LT1765-5
TYPICAL PERFORMANCE CHARACTERISTICS
Minimum Input Voltage for
2.5V Out
3.5
300
V
IN
= 15V
3.3
INPUT VOLTAGE (V)
V
IN
CURRENT (μA)
0.1
0.01
LOAD CURRENT (A)
1
1765 G07
SHDN
Supply Current
250
200
150
100
50
0
3.1
2.9
2.7
2.5
0.001
0
0.2
0.4 0.6 0.8
1
1.2
SHUTDOWN VOLTAGE (V)
1.4
1765 G08
Input Supply Current
1200
1000
V
IN
CURRENT (μA)
800
600
400
200
0
0
5
10
15
20
INPUT VOLTAGE (V)
25
30
1765 G09
Current Limit Foldback
4
40
SWITCH PEAK CURRENT (A)
FB INPUT CURRENT (μA)
UNDERVOLTAGE
LOCKOUT
3
SWITCH CURRENT
2
30
20
1
FB CURRENT
0
10
0
0.2
0.4
0.6
0.8
FEEDBACK VOLTAGE (V)
1
0
1.2
1765 G10
Maximum Load Current,
V
OUT
= 5V
3.0
3.0
Maximum Load Current,
V
OUT
= 2.5V
2.8
OUTPUT CURRENT (A)
L = 4.7μH
OUTPUT CURRENT (A)
L = 4.7μH
2.8
2.6
L = 2.2μH
2.6
L = 1.5μH
2.4
2.4
L = 2.2μH
2.2
L = 1.5μH
2.0
0
5
10
15
INPUT VOLTAGE (V)
20
25
1765 G11
2.2
0
5
10
15
INPUT VOLTAGE (V)
20
25
1765 G12
1765fd
5
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