LINEAR TECHNOLOGY LT1765, LT1765-1.8, LT1765-2.5, LT1765-3.3, LT1765-5 Technical data

查询LT1765EFE供应商

FEATURES

■

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

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APPLICATIO S

■

DSL Modems

■

Portable Computers

■

Regulated Wall Adapters

■

Battery-Powered Systems

■

Distributed Power

LT1765/LT1765-1.8/LT1765-2.5/

LT1765-3.3/LT1765-5

Monolithic 3A, 1.25MHz

Step-Down Switching Regulator

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DESCRIPTIO

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 consistent
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 reduc­tion of input and output filtering components and permits
the use of chip inductors.

, LTC and LT are registered trademarks of Linear Technology Corporation.

* Patent Pending

TYPICAL APPLICATIO

INPUT

5V

2.2µF

CERAMIC

ONOFF

V

IN

SYNC

BOOST

LT1765-3.3

GND

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Efficiency vs Load Current5V to 3.3V Step-Down Converter

CMDSH-3

0.18µF

V

SW

FBSHDN

V

C

2.2nF

1.5µH

UPS120

OUTPUT

3.3V

2.5A

4.7µF
CERAMIC

1765 TA01

90

85

80

EFFICIENCY (%)

75

70

0

0.5

1.0

SWITCH CURRENT (A)

VIN = 10V
V

OUT

1.5

= 5V

2.0

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LT1765/LT1765-1.8/LT1765-2.5/

FE PACKAGE

16-LEAD PLASTIC TSSOP

1

2

3

4

5

6

7

8

TOP VIEW

16

15

14

13

12

11

10

9

GND

BOOST

V

IN

V

IN

SW

SW

NC

GND

GND

NC

SYNC

V

C

FB

SHDN

NC

GND

17

LT1765-3.3/LT1765-5

WW

W

ABSOLUTE AXI U RATI GS

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(Note 1)

Input Voltage .......................................................... 25V

BOOST Pin Above SW ............................................ 20V

Max BOOST Pin Voltage .......................................... 35V

SHDN Pin ............................................................... 25V

FB Pin Current ....................................................... 1mA

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PACKAGE/ORDER I FOR ATIO

ORDER PART

TOP VIEW

BOOST

1

V

2

IN

SW

3

GND

4

S8 PACKAGE

8-LEAD PLASTIC SO

T

= 125°C, θJA = 90°C/W,

JMAX

θ

JC(PIN 4)

GROUND PIN CONNECTED TO

LARGE COPPER AREA

= 30°C/W

8

SYNC

V

7

C

FB

6

SHDN

5

NUMBER

LT1765ES8

S8 PART

MARKING

1765

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

ORDER PART

NUMBER

LT1765EFE
LT1765EFE-1.8
LT1765EFE-2.5
LT1765EFE-3.3
LT1765EFE-5

FE PART MARKING

1765EFE

θJA = 45°C/W, θ

EXPOSED PAD (PIN 17) SOLDERED TO LARGE

COPPER PLANE

JC(PAD)

= 10°C/W

1765EFE18
1765EFE25
1765EFE33

1765EFE-5

Consult LTC Marketing for parts specified with wider operating temperature ranges.

ELECTRICAL CHARACTERISTICS

The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
VIN = 15V, VC = 0.8V, Boost = VIN + 5V, SHDN, SYNC and switch open unless otherwise noted.

PARAMETER CONDITIONS MIN TYP MAX UNITS

Maximum Switch Current Limit 346 A

Oscillator Frequency 3.3V < VIN < 25V ● 1.1 1.25 1.6 MHz

Switch On Voltage Drop I = 3A ● 270 430 mV

VIN Undervoltage Lockout (Note 3) ● 2.47 2.6 2.73 V

VIN Supply Current ● 1 1.3 mA

Shutdown Supply Current V

Feedback Voltage 3V < VIN < 25V, 0.4V < VC < 0.9V LT1765 (Adj) 1.182 1.2 1.218 V

2

= 0V, VIN = 25V, VSW = 0V 15 35 µA

SHDN

(Note 3)

LT1765-1.8 ● 1.764 1.8 1.836 V

LT1765-2.5 ● 2.45 2.5 2.55 V

LT1765-3.3 ● 3.234 3.3 3.366 V

LT1765-5 ● 4.9 5 5.1 V

● 55 µA

● 1.176 1.224 V

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LT1765/LT1765-1.8/LT1765-2.5/

LT1765-3.3/LT1765-5

ELECTRICAL CHARACTERISTICS

The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.

= 15V, VC = 0.8V, Boost = VIN + 5V, SHDN, SYNC and switch open unless otherwise noted.

V

IN

PARAMETER CONDITIONS MIN TYP MAX UNITS

FB Input Current LT1765 (Adj) ● – 0.25 – 0.5 µA

FB Input Resistance LT1765 ● 10.5 15 21 kΩ

LT1765-1.8
LT1765-3.3
LT1765-5

FB Error Amp Voltage Gain 0.4V < VC < 0.9V 150 350

FB Error Amp Transconductance ∆IVC = ±10µA ● 500 850 1300 µMho

VC Pin Source Current VFB = V

VC Pin Sink Current VFB = V

VC Pin to Switch Current Transconductance 5 A/V

VC Pin Minimum Switching Threshold Duty Cycle = 0% 0.4 V

VC Pin 3A ISW Threshold 0.9 V

Maximum Switch Duty Cycle VC = 1.2V, ISW = 800mA, VIN = 6V 85 90 %

Minimum Boost Voltage Above Switch ISW = 3A ● 1.8 2.7 V

Boost Current ISW = 1A (Note 4) ● 20 30 mA

I

SW

SHDN Threshold Voltage ● 1.27 1.33 1.40 V

SHDN Threshold Current Hysteresis ● 4710 µA

SHDN Input Current (Shutting Down) SHDN = 60mV Above Threshold ● –7 –10 –13 µA

SYNC Threshold Voltage 1.5 2.2 V

SYNC Input Frequency 1.6 2 MHz

SYNC Pin Resistance I

Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.

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.

SYNC

– 17% ● 80 120 160 µA

NOM

+ 17% ● 70 110 180 µA

NOM

= 3A (Note 4) ● 70 140 mA

= 1mA 20 kΩ

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.

● 14.7 21 30 kΩ

● 19 27.5 39 kΩ

● 29 42 60 kΩ

● 80 %

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LT1765/LT1765-1.8/LT1765-2.5/

VIN (V)

0 5 10 15 20 25 30

V

IN

CURRENT (µA)

1765 G05

7

6

5

4

3

2

1

0

SHDN = 0V

LT1765-3.3/LT1765-5

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TYPICAL PERFOR A CE CHARACTERISTICS

FB vs Temperature (Adj)

1.220

1.215

1.210

1.205

1.200

1.195

FB VOLTAGE (V)

1.190

1.185

1.180
–50

050

–25 25 75 125

TEMPERATURE (°C)

SHDN Threshold vs Temperature

1.40

1.38

1.36

1.34

SHDN THRESHOLD (V)

1.32

100

1765 G01

350

300

250

200

150

100

SWITCH VOLTAGE (mV)

50

0

0

SWITCH CURRENT (A)

Oscillator FrequencySwitch On Voltage Drop

1.50

TA = 125°C

TA = –40°C

TA = 25°C

1

23

1765 G02

1.45

1.40

1.35

1.30

1.25

FREQUENCY (MHz)

1.20

1.15

1.10
–25 0 25 50 75 100 125

–50

TEMPERATURE (°C)

SHDN Supply Current vs V

1765 G03

IN

1.30
–50

–25 0 25 50 75 100 125

TEMPERATURE (°C)

1765 G04

SHDN IP Current vs Temperature

–12

–10

–8

–6

–4

SHDN INPUT (µA)

–2

0

–50

SHUTTING DOWN

STARTING UP

–25 0 25 50 75 100 125

TEMPERATURE (°C)

1765 G06

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LT1765/LT1765-1.8/LT1765-2.5/

1765 G11

INPUT VOLTAGE (V)

0 5 10 15 20 25

OUTPUT CURRENT (A)

3.0

2.8

2.6

2.4

2.2

2.0

L = 4.7µH

L = 2.2µH

L = 1.5µH

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TYPICAL PERFOR A CE CHARACTERISTICS

Minimum Input Voltage for

2.5V Out

3.5

3.3

3.1

2.9

INPUT VOLTAGE (V)

2.7

SHDN Supply Current

300

VIN = 15V

250

200

150

CURRENT (µA)

IN

100

V

50

LT1765-3.3/LT1765-5

Input Supply Current

1200

1000

800

600

CURRENT (µA)

IN

400

V

200

UNDERVOLTAGE
LOCKOUT

2.5

0.001 0.01

SWITCH PEAK CURRENT (A)

LOAD CURRENT (A)

0.1 1

Current Limit Foldback

4

3

SWITCH CURRENT

2

1

FB CURRENT

0

0 0.2

0.4 0.6 0.8 1 1.2

FEEDBACK VOLTAGE (V)

1765 G07

0

0

0.2 0.4 0.6 0.8 1 1.2 1.4
SHUTDOWN VOLTAGE (V)

40

FB INPUT CURRENT (µA)

30

20

10

0

1765 G10

Maximum Load Current,
V

= 2.5V

OUT

3.0

0

0 5 10 15 20 25 30

1765 G08

Maximum Load Current,
V

= 5V

OUT

INPUT VOLTAGE (V)

1765 G09

2.8

2.6

OUTPUT CURRENT (A)

2.4

2.2
05

INPUT VOLTAGE (V)

L = 4.7µH

L = 2.2µH

L = 1.5µH

10 15 20 25

1765 G12

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LT1765/LT1765-1.8/LT1765-2.5/
LT1765-3.3/LT1765-5

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PI FU CTIO S

FB: The feedback pin is used to set output voltage using
an external voltage divider (adjustable version) that gen­erates 1.2V at the pin when connected to the desired
output voltage. The fixed voltage 1.8V, 2.5V, 3.3V and 5V
versions have the divider network included internally and
the FB pin is connected directly to the output. If required,
the current limit can be reduced during start up or short­circuit when the FB pin is below 0.5V (see the Current Limit
Foldback graph in the Typical Performance Characteris­tics section). An impedance of less than 5kΩ on the
adjustable version at the FB pin is needed for this feature
to operate.

BOOST: The BOOST pin is used to provide a drive voltage,
higher than the input voltage, to the internal bipolar NPN
power switch.

VIN: This is the collector of the on-chip power NPN switch.
This pin powers the internal circuitry and internal regula­tor. At NPN switch on and off, high di/dt edges occur on
this pin. Keep the external bypass capacitor and catch
diode close to this pin. All trace inductance on this path will
create a voltage spike at switch off, adding to the V
voltage across the internal NPN. Both VIN pins of the
TSSOP package must be shorted together on the PC
board.

GND: The GND pin acts as the reference for the regulated
output, so load regulation will suffer if the “ground” end of
the load is not at the same voltage as the GND pin of the
IC. This condition will occur when load current or other
currents flow through metal paths between the GND pin
and the load ground point. Keep the ground path short
between the GND pin and the load and use a ground plane
when possible. Keep the path between the input bypass
and the GND pin short. The exposed GND pad and/or GND
pins of the package are directly attached to the internal tab.
These pins/pad should be attached to a large copper area
to reduce thermal resistance.

CE

VSW: The switch pin is the emitter of the on-chip power
NPN switch. This pin is driven up to the input pin voltage
during switch on time. Inductor current drives the switch
pin negative during switch off time. Negative voltage must
be clamped with an external catch diode with a V
Both V
together on the PC board.

SYNC: The sync pin is used to synchronize the internal
oscillator to an external signal. It is directly logic compat­ible and can be driven with any signal between 20% and
80% duty cycle. The synchronizing range is from 1.6MHz
to 2MHz. See Synchronization section in Applications
Information for details. When not in use, this pin should be
grounded.

SHDN: The shutdown pin is used to turn off the regulator
and to reduce input drain current to a few microamperes.
The 1.33V threshold can function as an accurate under­voltage lockout (UVLO), preventing the regulator from
operating until the input voltage has reached a predeter­mined level. Float or pull high to put the regulator in the
operating mode.

VC: The VC pin is the output of the error amplifier and the
input of the peak switch current comparator. It is normally
used for frequency compensation, but can do double duty
as a current clamp or control loop override. This pin sits
at about 0.4V for very light loads and 0.9V at maximum
load. It can be driven to ground to shut off the output.

pins of the TSSOP package must be shorted

SW

<0.8V.

BR

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