Linear Technology LT1767EMS8-1.8, LT1767EMS8, LT1767EMS8E-5, LT1767EMS8E-3.3, LT1767EMS8E-2.5 Datasheet

FEATURES

■

1.5A Switch in a Small MSOP Package

■

Constant 1.25MHz Switching Frequency

■

High Power Exposed Pad (MS8E) Package

■

Wide Operating Voltage Range: 3V to 25V

■

High Efficiency 0.22Ω Switch

■

1.2V Feedback Reference Voltage

■

Fixed Output Voltages of 1.8V, 2.5V, 3.3V, 5V

■

2% Overall Output Tolerance

■

Uses Low Profile Surface Mount Components

■

Low Shutdown Current: 6µA

■

Synchronizable to 2MHz

■

Current Mode Loop Control

■

Constant Maximum Switch Current Rating at All Duty
Cycles*

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APPLICATIO S

■

DSL Modems

■

Portable Computers

■

Wall Adapters

■

Battery-Powered Systems

■

Distributed Power

LT1767/LT1767-1.8/

LT1767-2.5/LT1767-3.3/LT1767-5

Monolithic 1.5A, 1.25MHz

Step-Down Switching Regulators

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DESCRIPTIO

The LT®1767 is a 1.25MHz monolithic buck switching
regulator. A high efficiency 1.5A, 0.22Ω switch is included
on the die together with all the control circuitry required to
complete 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 range. A low
dropout internal regulator maintains consistent perfor­mance over a wide range of inputs from 24V systems to Li­Ion batteries. An operating supply current of 1mA im­proves efficiency, especially at lower output currents.
Shutdown reduces quiescent current to 6µA. Maximum
switch current remains constant at all duty cycles. Syn­chronization allows an external logic level signal to in­crease the internal oscillator from 1.4MHz to 2MHz.

The LT1767 is available in an 8-pin MSOP fused leadframe
package and a low thermal resistance exposed pad pack­age. Full cycle-by-cycle short-circuit protection 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

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TYPICAL APPLICATIO

12V to 3.3V Step-Down Converter

C2

0.1µF

V

IN

12V

C3

2.2µF

CERAMIC

*MAXIMUM OUTPUT CURRENT IS SUBJECT TO THERMAL DERATING.

OPEN

OR

HIGH

= ON

V

IN

SYNC

BOOST

LT1767-3.3

GND

V

SW

FBSHDN

V

C

C

C

1.5nF

R

C

4.7k

CMDSH-3

5µH

D1
UPS120

Efficiency vs Load Current

95

D2

90

L1

OUTPUT

3.3V

1.2A*

C1
10µF
CERAMIC

1767 TA01

85

80

EFFICIENCY (%)

75

70

0.2 0.4 0.6 0.8 1 1.2 1.4

0

LOAD CURRENT (A)

VIN = 10V

= 5V

V

OUT

VIN = 5V

= 3.3V

V

OUT

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1767 TA01a

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LT1767/LT1767-1.8/
LT1767-2.5/LT1767-3.3/LT1767-5

WW

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ABSOLUTE MAXIMUM RATINGS

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(Note 1)

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

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

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

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

FB Pin Voltage .......................................................... 6V

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

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W

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PACKAGE/ORDER INFORMATION

ORDER PART NUMBER

TOP VIEW

BOOST

1

V

2

IN

3

SW

4

GND

MS8 PACKAGE

8-LEAD PLASTIC MSOP

T

= 125°C, θJA = 110°C/W

JMAX

GROUND PIN CONNECTED
TO LARGE COPPER AREA

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

8
7
6
5

SYNC
V

C

FB
SHDN

LT1767EMS8
LT1767EMS8-1.8
LT1767EMS8-2.5
LT1767EMS8-3.3
LT1767EMS8-5

MS8 PART MARKING

LTLS
LTWG
LTWD
LTWE
LTWF

SYNC Pin Current .................................................. 1mA

Operating Junction Temperature Range (Note 2)

LT1767E .......................................... –40°C to 125°C

Storage Temperature Range ................ –65°C to 150°C

Lead Temperature (Soldering, 10 sec)................. 300°C

ORDER PART NUMBER

BOOST

1

V

2

IN

3

SW

4

GND

MS8E PACKAGE

8-LEAD PLASTIC MSOP

T

= 125°C, θJA = 40°C/W

JMAX

EXPOSED GND PAD
CONNECTED TO LARGE
COPPER AREA ON PCB

TOP VIEW

8
7
6
5

SYNC
V

C

FB
SHDN

LT1767EMS8E
LT1767EMS8E-1.8
LT1767EMS8E-2.5
LT1767EMS8E-3.3
LT1767EMS8E-5

MS8E PART MARKING

LTZG
LTZH
LTZJ
LTZK
LTZL

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 CONDITION MIN TYP MAX UNITS

Maximum Switch Current Limit TA = 0°C to 125°C 1.5 2 3 A

TA = < 0°C 1.3 3 A

Oscillator Frequency 3.3V < VIN < 25V 1.1 1.25 1.4 MHz

● 1.1 1.5 MHz

Switch On Voltage Drop ISW = –1.5A, 0°C ≤ TA ≤ 125°C and –1.3A, TA < 0°C 330 400 mV

● 500 mV

VIN Undervoltage Lockout (Note 3) ● 2.47 2.6 2.73 V
VIN Supply Current VFB = V
Shutdown Supply Current V

Feedback Voltage 3V < VIN < 25V, 0.4V < VC < 0.9V LT1767 (Adj) 1.182 1.2 1.218 V

FB Input Current LT1767 (Adj) ● – 0.25 –0.5 µA

SHDN

(Note 3) ● 1.176 1.224 V

+ 17% ● 1 1.3 mA

NOM

= 0V, VIN = 25V, VSW = 0V 6 20 µA

● 45 µA

LT1767-1.8 ● 1.764 1.8 1.836 V
LT1767-2.5 ● 2.45 2.5 2.55 V
LT1767-3.3 ● 3.234 3.3 3.366 V
LT1767-5 ● 4.9 5 5.1 V

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LT1767/LT1767-1.8/

TEMPERATURE (°C)

–50

–25 0 25 50 75 100 125

FREQUENCY (MHz)

1767 G03

1.50

1.45

1.40

1.35

1.30

1.25

1.20

1.15

1.10

LT1767-2.5/LT1767-3.3/LT1767-5

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 CONDITION MIN TYP MAX UNITS

FB Input Resistance LT1767-1.8 ● 10.5 15 21 kΩ

LT1767-2.5
LT1767-3.3 ● 19 27.5 39 kΩ
LT1767-5

Error Amp Voltage Gain 0.4V < VC < 0.9V 150 350
Error Amp Transconductance ∆IVC = ±10µA ● 500 850 1300 µMho
VC Pin Source Current VFB = V
VC Pin Sink Current VFB = V

– 17% ● 80 120 160 µA

NOM

+ 17% ● 70 110 180 µA

NOM

VC Pin to Switch Current Transconductance 2.5 A/V
VC Pin Minimum Switching Threshold Duty Cycle = 0% 0.35 V
VC Pin 1.5A ISW Threshold 0.9 V
Maximum Switch Duty Cycle VC = 1.2V, ISW = 400mA 85 90 %

Minimum Boost Voltage Above Switch ISW = –1.5A, 0°C ≤ TA ≤ 125°C and –1.3A, TA < 0°C ● 1.8 2.7 V
Boost Current ISW = –0.5A (Note 4) ● 10 15 mA

ISW = –1.5A, 0°C ≤ TA ≤ 125°C and –1.3A, TA < 0°C (Note 4) ● 30 45 mA

SHDN Threshold Voltage ● 1.27 1.33 1.40 V
SHDN Input Current (Shutting Down) SHDN = 60mV Above Threshold ● –7 –10 –13 µA
SHDN Threshold Current Hysteresis SHDN = 100mV Below Threshold ● 4710 µA
SYNC Threshold Voltage 1.5 2.2 V
SYNC Input Frequency 1.5 2 MHz
SYNC Pin Resistance I

= 1mA 20 kΩ

SYNC

● 14.7 21 30 kΩ

● 29 42 60 kΩ

● 80 %

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

Note 2: The LT1767E 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.

TYPICAL PERFORMANCE CHARACTERISTICS

FB VOLTAGE (V)

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.

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FB vs Temperature (Adj) Switch On Voltage Drop Oscillator Frequency

1.22

1.21

1.20

1.19

1.18
–50

–25 0 25 50 75 100 125

TEMPERATURE (°C)

1767 G01

400

350

300

250

200

150

SWITCH VOLTAGE (mV)

100

50

0

0 0.5

SWITCH CURRENT (A)

125°C

25°C

–40°C

1 1.5

1767 G02

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LT1767/LT1767-1.8/
LT1767-2.5/LT1767-3.3/LT1767-5

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TYPICAL PERFOR A CE CHARACTERISTICS

SHDN Threshold vs Temperature SHDN Supply Current vs V

1.40

1.38

1.36

1.34

SHDN THRESHOLD (V)

1.32

1.30
–50

–25 0 25 50 75 100 125

TEMPERATURE (°C)

1767 G04

7

SHDN = 0V

6

5

4

3

CURRENT (µA)

IN

V

2

1

0

0 5 10 15 20 25 30

VIN (V)

IN

1767 G05

SHDN IP Current vs Temperature

–12

–10

–8

–6

–4

SHDN INPUT (µA)

–2

0

–25 0 25 50 75 100 125

–50

TEMPERATURE (°C)

Minimum Input Voltage for 2.5V Out SHDN Supply Current Input Supply Current

3.5

3.3

3.1

2.9

INPUT VOLTAGE (V)

2.7

300

VIN = 15V

250

200

150

CURRENT (µA)

IN

100

V

50

1200

1000

800

600

CURRENT (µA)

IN

400

V

200

MINIMUM

VOLTAGE

SHUTTING DOWN

STARTING UP

1767 G06

INPUT

2.5

0.001 0.01
LOAD CURRENT (A)

Current Limit Foldback

2.0

1.5

SWITCH CURRENT

1.0

0.5

SWITCH PEAK CURRENT (A)

0

0 0.2

FB CURRENT

0.4 0.6 0.8 1 1.2

FEEDBACK VOLTAGE (V)

0.1 1

1767 G07

1767 G10

0

0.2 0.4 0.6 0.8 1 1.2 1.4

0

SHUTDOWN VOLTAGE (V)

1767 G08

Maximum Load Current,
V

= 5V

OUT

40

FB INPUT CURRENT (µA)

30

20

10

0

1.5

1.3

1.1

0.9

OUTPUT CURRENT (A)

0.7

0.5
0 5 10 15 20 25

INPUT VOLTAGE (V)

L = 4.7µH

L = 2.2µH

L = 1.5µH

1767 G11

0

0 5 10 15 20 25 30

INPUT VOLTAGE (V)

Maximum Load Current,
V

= 2.5V

OUT

1.5

1.3

1.1

OUTPUT CURRENT (A)

0.9

0.7
05

10 15 20 25

INPUT VOLTAGE (V)

L = 4.7µH

L = 2.2µH

L = 1.5µH

sn1767 1767fas

1767 G09

1767 G12

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PIN FUNCTIONS

LT1767/LT1767-1.8/

LT1767-2.5/LT1767-3.3/LT1767-5

FB: The feedback pin is used to set output voltage using an
external voltage divider that generates 1.2V at the pin with
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 short-circuit 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 (adjustable part only) 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. Without this added voltage, the typical
switch voltage loss would be about 1.5V. The additional
boost voltage allows the switch to saturate and voltage
loss approximates that of a 0.22Ω FET structure.

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 in this path will
create a voltage spike at switch off, adding to the V
voltage across the internal NPN.

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

CE

when possible. Keep the path between the input bypass
and the GND pin short. The GND pin of the MS8 package
is directly attached to the internal tab. This pin should be
attached to a large copper area to improve thermal
resistance. The exposed pad of the MS8E package is also
connected to GND. This should be soldered to a large
copper area to improve its thermal resistance.

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 VBR <0.8V.

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 equal to
operating frequency, up 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 0.35V for very light loads and 0.9V at maximum
load. It can be driven to ground to shut off the output.

initial

sn1767 1767fas

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