Datasheet

ManualsBrandsLINEAR TECHNOLOGY ManualsPMICsPMIC - DC/DC voltage regulator Buck, Boost, Cuk, Flyback, Forward converter, SEPIC SOIC

LT1372/LT1377

500kHz and 1MHz

High Efficiency

1.5A Switching Regulators

■

Boost Regulators

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CCFL Backlight Driver

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Laptop Computer Supplies

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Multiple Output Flyback Supplies

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Inverting Supplies

The LT

1372/LT1377 are monolithic high frequency

switching regulators. They can be operated in all standard

switching configurations including boost, buck, flyback,

forward, inverting and “Cuk.” A 1.5A high efficiency switch

is included on the die, along with all oscillator, control and

protection circuitry. All functions of the LT1372/LT1377

are integrated into 8-pin SO/PDIP packages.

The LT1372/LT1377 typically consumes only 4mA quies-

cent current and has higher efficiency than previous parts.

High frequency switching allows for very small inductors

to be used. All surface mount components consume less

than 0.5 square inch of board space.

New design techniques increase flexibility and maintain

ease of use. Switching is easily synchronized to an exter-

nal logic level source. A logic low on the shutdown pin

reduces supply current to 12µA. Unique error amplifier

circuitry can regulate positive or negative output voltage

while maintaining simple frequency compensation tech-

niques. Nonlinear error amplifier transconductance re-

duces output overshoot on start-up or overload recovery.

Oscillator frequency shifting protects external compo-

nents during overload conditions.

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Faster Switching with Increased Efficiency

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Uses Small Inductors: 4.7µH

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All Surface Mount Components

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Only 0.5 Square Inch of Board Space

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Low Minimum Supply Voltage: 2.7V

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Quiescent Current: 4mA Typ

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Current Limited Power Switch: 1.5A

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Regulates Positive or Negative Outputs

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Shutdown Supply Current: 12µA Typ

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Easy External Synchronization

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8-Pin SO or PDIP Packages

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

12V Output Efficiency

OUTPUT CURRENT (A)

0.01

EFFICIENCY (%)

0.1 1

LT1372 • TA02

100

= 5V

5V-to-12V Boost Converter

LT1372/LT1377

6, 7

GND

LT1372 • TA01

S/S

L1*

4.7µH

C1**

22µF

C4**

22µF

0.047µF

0.0047µF

6.19k

53.6k

OUT

†

12V

MBRS120T3

OFF

*FOR LT1372 USE 10µH

COILCRAFT DO1608-472 (4.7µH) OR

COILCRAFT DT3316-103 (10µH) OR

SUMIDA CD43-4R7 (4.7µH) OR

SUMIDA CD73-100KC (10µH) OR

**AVX TPSD226M025R0200

4.7µH

10µH

OUT

(LT1377)

0.25A

0.35A

OUT

(LT1372)

0.29A

†

MAX I

OUT

+ +

FEATURES

DESCRIPTIO

APPLICATIO S

TYPICAL APPLICATIO

Summary of content (12 pages)

PAGE 1
LT1372/LT1377 500kHz and 1MHz High Efficiency 1.5A Switching Regulators U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO Faster Switching with Increased Efficiency Uses Small Inductors: 4.7µH All Surface Mount Components Only 0.5 Square Inch of Board Space Low Minimum Supply Voltage: 2.7V Quiescent Current: 4mA Typ Current Limited Power Switch: 1.
PAGE 2
LT1372/LT1377 W W W AXI U U ABSOLUTE RATI GS U U W PACKAGE/ORDER I FOR ATIO (Note 1) Supply Voltage ....................................................... 30V Switch Voltage LT1372/LT1377 .................................................. 35V LT1372HV .......................................................... 42V S/S Pin Voltage ....................................................... 30V Feedback Pin Voltage (Transient, 10ms) .............. ±10V Feedback Pin Current ...............................
PAGE 3
LT1372/LT1377 ELECTRICAL CHARACTERISTICS The ● denotes specifcatons which appy over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 5V, VC = 0.6V, VFB = VREF, VSW, S/S and NFB pins open, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN Maximum Switch Duty Cycle TYP 85 ● 130 Output Switch Breakdown Voltage 260 ns % LT1372/LT1377 LT1372HV 0°C ≤ TJ ≤ 125°C – 40°C ≤ TJ < 0°C (I Grade) ● 35 47 V ● 42 40 47 V V 0.5 0.8 Ω 1.9 1.7 2.7 2.
PAGE 4
LT1372/LT1377 U W TYPICAL PERFOR A CE CHARACTERISTICS 2.0 18 1.8 SHUTDOWN DELAY (µs) 14 1.4 12 1.2 10 1.0 SHUTDOWN DELAY 8 0.8 6 0.6 4 0.4 2 0.2 0 –50 –25 0 SHUTDOWN THRESHOLD (V) 1.6 SHUTDOWN THRESHOLD 0 25 50 75 100 125 150 TEMPERATURE (°C) 3.0 2.5 400 fSYNC = 700kHz (LT1372) fSYNC = 1.4MHz (LT1377) 2.0 LT1377 1.5 LT1372 1.0 0.5 0 –50 –25 2 1 0 –1 –2 –3 –4 –5 –1 0 1 2 3 4 5 6 S/S PIN VOLTAGE (V) 7 8 90 80 70 60 50 40 30 VC THRESHOLD 0.
PAGE 5
LT1372/LT1377 U U U PI FU CTIO S VIN (Pin 5): Bypass input supply pin with 10µF or more. The part goes into undervoltage lockout when VIN drops below 2.5V. Undervoltage lockout stops switching and pulls the VC pin low. VC (Pin 1): The compensation pin is used for frequency compensation, current limiting and soft start. It is the output of the error amplifier and the input of the current comparator. Loop frequency compensation can be performed with an RC network connected from the VC pin to ground.
PAGE 6
LT1372/LT1377 U OPERATIO The LT1372/LT1377 are current mode switchers. This means that switch duty cycle is directly controlled by switch current rather than by output voltage. Referring to the block diagram, the switch is turned “On” at the start of each oscillator cycle. It is turned “Off” when switch current reaches a predetermined level. Control of output voltage is obtained by using the output of a voltage sensing error amplifier to set current trip level. This technique has several advantages.
PAGE 7
LT1372/LT1377 U W U U APPLICATIO S I FOR ATIO Positive fixed voltage versions are available (consult Linear Technology marketing). Negative Output Voltage Setting The LT1372/LT1377 develops a – 2.49V reference (VNFR) from the NFB pin to ground. Output voltage is set by connecting the NFB pin to an output resistor divider (Figure 2). The – 30µA NFB pin bias current (INFB) can cause output voltage errors and should not be ignored. This has been accounted for in the formula in Figure 2.
PAGE 8
LT1372/LT1377 U W U U APPLICATIO S I FOR ATIO Choosing the Inductor For most applications the inductor will fall in the range of 2.2µH to 22µH. Lower values are chosen to reduce physical size of the inductor. Higher values allow more output current because they reduce peak current seen by the power switch, which has a 1.5A limit. Higher values also reduce input ripple voltage and reduce core loss.
PAGE 9
LT1372/LT1377 U W U U APPLICATIO S I FOR ATIO Table 1. Surface Mount Solid Tantalum Capacitor ESR and Ripple Current E CASE SIZE IRIPPLE = ESR (MAX Ω) RIPPLE CURRENT (A) 0.1 to 0.3 0.7 to 0.9 0.7 to 1.1 0.4 0.1 to 0.3 0.9 to 2.0 0.7 to 1.1 0.36 to 0.24 0.2 (Typ) 1.8 to 3.0 0.5 (Typ) 0.22 to 0.17 2.5 to 10 0.16 to 0.08 AVX TPS, Sprague 593D AVX TAJ 0.
PAGE 10
LT1372/LT1377 U W U U APPLICATIO S I FOR ATIO Frequency Compensation Loop frequency compensation is performed on the output of the error amplifier (VC pin) with a series RC network. The main pole is formed by the series capacitor and the output impedance (≈500kΩ) of the error amplifier. The pole falls in the range of 2Hz to 20Hz. The series resistor creates a “zero” at 1kHz to 5kHz, which improves loop stability and transient response.
PAGE 11
LT1372/LT1377 U TYPICAL APPLICATIONS N Positive-to-Negative Converter with Direct Feedback VIN 2.7V TO 16V + C1 22µF OFF VIN VSW LT1372/LT1377 NFB VC 2 D2 P6KE-15A D3 1N4148 1 • 8 4 + • R2 2.49k 1% D1 MBRS130LT3 3 VIN 2.7V TO 13V –VOUT† –5V R3 2.49k 1% 6, 7 R1 13k 1% C4 47µF 3 GND 1 + OFF C1 22µF 2 *COILTRONICS CTX10-2 (407) 241-7876 † MAX IOUT IOUT VIN 0.3A 3V 0.5A 5V 0.
PAGE 12
LT1372/LT1377 U TYPICAL APPLICATIONS N 2 Li-Ion Cell to 5V SEPIC Converter VIN 4V TO 9V OFF + ON 4 S/S C1 33µF 20V L1A* 10µH 5 VIN 8 VSW • VC + L1B* 10µH 1 6, 7 VOUT† 5V R2 18.7k 1% C2 1µF LT1372/LT1377 FB 2 GND MBRS130LT3 • R1 2k C5 0.0047µF C4 0.047µF U PACKAGE DESCRIPTION C3 100µF 10V C1 = AVX TPSD 336M020R0200 C2 = TOKIN 1E105ZY5U-C103-F C3 = AVX TPSD107M010R0100 *SINGLE INDUCTOR WITH TWO WINDINGS COILTRONICS CTX10-1 † MAX IOUT IOUT 0.45A 0.55A 0.65A 0.72A R3 6.