Datasheet

ManualsBrandsLINEAR TECHNOLOGY ManualsPMICsPMIC - DC/DC voltage regulator Buck, Boost, Cuk, Flyback, Forward converter, SEPIC D2PAK

LT1370

sn1370 1370fs

500kHz High Efficiency

6A Switching Regulator

The LT

1370 is a monolithic high frequency current mode

switching regulator. It can be operated in all standard

switching configurations including boost, buck, flyback,

forward, inverting and “Cuk.” A 6A high efficiency switch

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

protection circuitry.

The LT1370 typically consumes only 4.5mA quiescent

current and has higher efficiency than previous parts.

High frequency switching allows for very small inductors

to be used.

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

reduces output overshoot on start-up or overload recov-

ery. Oscillator frequency shifting protects external com-

ponents during overload conditions.

DESCRIPTION

■

Faster Switching with Increased Efficiency

■

Uses Small Inductors: 4.7µH

■

All Surface Mount Components

■

Low Minimum Supply Voltage: 2.7V

■

Quiescent Current: 4.5mA Typ

■

Current Limited Power Switch: 6A

■

Regulates Positive or Negative Outputs

■

Shutdown Supply Current: 12µA Typ

■

Easy External Synchronization

■

Switch Resistance: 0.065Ω Typ

TYPICAL APPLICATION

FEATURES

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

■

Boost Regulators

■

Laptop Computer Supplies

■

Multiple Output Flyback Supplies

■

Inverting Supplies

APPLICATIONS

5V to 12V Boost Converter

LT1370

GND

LT1370 • TA01

S/S

L1*

C1**

22µF

25V

C4**

22µF

25V

× 2

0.047µF

0.0047µF

6.19k

53.6k

OUT

†

12V

MBRD835L

OFF

COILTRONICS

UP2-4R7 (4.7µH)

UP4-100 (10µH)

AVX TPSD226M025R0200

+ +

4.7µH

10µH

OUT

1.8A

†

MAX I

OUT

12V Output Efficiency

LOAD CURRENT (A)

EFFICIENCY (%)

1.0 1.2 1.4 1.6 1.80.2 0.4 0.6 0.8 2.0

LT1370 • TA02

= 5V

L = 10µH

Summary of content (16 pages)

PAGE 1
LT1370 500kHz High Efficiency 6A Switching Regulator U FEATURES DESCRIPTION ■ The LT ®1370 is a monolithic high frequency current mode switching regulator. It can be operated in all standard switching configurations including boost, buck, flyback, forward, inverting and “Cuk.” A 6A high efficiency switch is included on the die, along with all oscillator, control and protection circuitry. ■ ■ ■ ■ ■ ■ ■ ■ ■ Faster Switching with Increased Efficiency Uses Small Inductors: 4.
PAGE 2
LT1370 W W W AXI U U ABSOLUTE RATI GS Supply Voltage ....................................................... 30V Switch Voltage LT1370 ............................................................... 35V LT1370HV .......................................................... 42V S/S, SHDN, SYNC Pin Voltage ................................ 30V Feedback Pin Voltage (Transient, 10ms) .............. ±10V Feedback Pin Current ...........................................
PAGE 3
LT1370 ELECTRICAL CHARACTERISTICS VIN = 5V, VC = 0.6V, VFB = VREF, VSW, S/S and NFB pins open, TA = 25°C unless otherwise noted. SYMBOL AV f PARAMETER CONDITIONS MIN TYP MAX UNITS Error Amplifier Clamp Voltage High Clamp, VFB = 1V 1.5 1.8 2.30 V Low Clamp, VFB = 1.5V 0.2 0.3 0.52 Error Amplifier Voltage Gain VC Pin Threshold Duty Cycle = 0% Switching Frequency 2.7V ≤ VIN ≤ 25V 0°C ≤ TJ ≤ 125°C – 40°C ≤ TJ ≤ 0°C (I-Grade) Maximum Switch Duty Cycle V/ V 0.9 1.1 1.
PAGE 4
LT1370 U W TYPICAL PERFORMANCE CHARACTERISTICS Switch Saturation Voltage vs Switch Current Switch Current Limit vs Duty Cycle 8.2 550 SWITCH CURRENT LIMIT (A) 75°C 400 25°C 350 300 0°C 250 200 150 100 2.8 7.8 7.6 7.4 7.2 4 2 3 SWITCH CURRENT (A) 5 10 20 30 40 50 60 70 80 90 100 DUTY CYCLE (%) 0 6 20 2.0 18 1.8 SHUTDOWN DELAY (µs) 1.4 12 1.2 10 1.0 SHUTDOWN DELAY 0.8 6 0.6 4 0.4 2 0.2 0 –50 –25 0 SHUTDOWN THRESHOLD (V) 1.
PAGE 5
LT1370 U W TYPICAL PERFORMANCE CHARACTERISTICS VC Pin Threshold and High Clamp Voltage vs Temperature Feedback Input Current vs Temperature 2.2 1.8 1.6 1.4 1.2 VC THRESHOLD 0 25 50 75 100 125 150 TEMPERATURE (°C) 700 NEGATIVE FEEDBACK INPUT CURRENT (µA) VC HIGH CLAMP FEEDBACK INPUT CURRENT (nA) VC VOLTAGE (V) 0 800 2.0 1.
PAGE 6
LT1370 W BLOCK DIAGRAM VIN SHUTDOWN DELAY AND RESET SW LOW DROPOUT 2.3V REG ANTI-SAT S/S SYNC LOGIC OSC DRIVER SWITCH 5:1 FREQUENCY SHIFT + 100k NFB NFBA – COMP 50k – FB + 1.245V REF + EA IA VC GND SENSE AV ≈ 20 0.005Ω – GND LT1370 • BD U OPERATION The LT1370 is a current mode switcher. This means that switch duty cycle is directly controlled by switch current rather than by output voltage.
PAGE 7
LT1370 U OPERATION Unique error amplifier circuitry allows the LT1370 to directly regulate negative output voltages. The negative feedback amplifier’s 100k source resistor is brought out for negative output voltage sensing. The NFB pin regulates at – 2.48V while the amplifier output internally drives the FB pin to 1.245V. This architecture, which uses the same main error amplifier, prevents duplicating functions and maintains ease of use. Consult LTC Marketing for units that can regulate down to – 1.25V.
PAGE 8
LT1370 U U W U APPLICATIO S I FOR ATIO Shutdown and Synchronization The device has a dual function S/S pin which is used for both shutdown and synchronization. This pin is logic level compatible and can be pulled high, tied to VIN or left floating for normal operation. A logic low on the S/S pin activates shutdown, reducing the part’s supply current to 12µA. Typical synchronization range is from 1.05 to 1.8 times the part’s natural switching frequency, but is only guaranteed between 600kHz and 800kHz.
PAGE 9
LT1370 U U W U APPLICATIO S I FOR ATIO ) ) V V (V –V ) IPEAK = (IOUT) OUT + IN OUT IN VIN 2(f)(L)(VOUT) VIN = Minimum input voltage f = 500kHz switching frequency 3. Decide if the design can tolerate an “open” core geometry, like a rod or barrel, which has high magnetic field radiation, or whether it needs a closed core, like a toroid, to prevent EMI problems.
PAGE 10
LT1370 U U W U APPLICATIO S I FOR ATIO Input Capacitors Output Diode The input capacitor of a boost converter is less critical due to the fact that the input current waveform is triangular and does not contain large squarewave currents as is found in the output capacitor. Capacitors in the range of 10µF to 100µF with an ESR of 0.1Ω or less work well up to full 6A switch current. Higher ESR capacitors may be acceptable at low switch currents.
PAGE 11
LT1370 U U W U APPLICATIO S I FOR ATIO Layout Considerations For maximum efficiency, LT1370 switch rise and fall times are made as short as possible. To prevent radiation and high frequency resonance problems, proper layout of the components connected to the switch node is essential. B field (magnetic) radiation is minimized by keeping output diode, switch pin and output bypass capacitor leads as short as possible. Figure 3 shows recommended positions for these components.
PAGE 12
LT1370 U TYPICAL APPLICATIONS N Positive-to-Negative Converter with Direct Feedback VIN 2.7V TO 13V + T1* 2 D2 P6KE-15A D3 1N4148 1 • C1 100µF VIN ON OFF VSW S/S 4 + • C4 100µF ×2 R2 2.49k 1% D1 MBRD835L LT1370 NFB VC C3 0.0047µF R3 2.49k 1% GND C2 0.047µF R1 2k –VOUT† –5V 3 *BH ELECTRONICS 501-0726 †MAX I OUT IOUT VIN 1.75A 3V 2.25A 5V 3A 9V LT1370 • TA03 Dual Output Flyback Converter with Overvoltage Protection R2 6.19k 1% R1 68.1k 1% VIN 2.
PAGE 13
LT1370 U TYPICAL APPLICATIONS N Two Li-Ion Cells to 5V SEPIC Converter** VIN 4V TO 9V L1A* 6.8µH VIN ON OFF • VSW S/S C1 33µF 20V FB GND • VC C3 100µF 10V ×2 + L1B* 6.8µH R1 2k C4 0.047µF VOUT† 5V R2 18.7k 1% C2 4.7µF LT1370 + D1 MBRD835L R3 6.19k 1% C5 0.0047µF LT1370 • TA05 C1 = AVX TPSD 336M020R0200 C2 = TOKIN 1E475ZY5U-C304 C3 = AVX TPSD107M010R0100 * BH ELECTRONICS 501-0726 ** INPUT VOLTAGE MAY BE GREATER OR LESS THAN OUTPUT VOLTAGE †MAX I OUT IOUT VIN 2A 4V 2.2A 5V 2.6A 7V 2.
PAGE 14
LT1370 U TYPICAL APPLICATIONS N Laser Power Supply 0.01µF 5kV 1800pF 10kV 47k 5W 1800pF 10kV 8 11 L1 1 4 5 HV DIODES 3 2 LASER + 2.2µF Q1 0.47µF 150Ω L2 82µH MUR405 VIN 12V TO 25V VSW 10k VIN + Q2 10k FB LT1370 2.2µF VC GND 0.1µF VIN 1N4002 (ALL) 190Ω 1% + 10µF L1 = COILTRONICS CTX02-11128 L2 = GOWANDA GA40-822K Q1, Q2 = ZETEX ZTX849 0.47µF = WIMA 3X 0.
PAGE 15
LT1370 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. R Package 7-Lead Plastic DD Pak (LTC DWG # 05-08-1462) 0.256 (6.502) 0.060 (1.524) TYP 0.060 (1.524) 0.390 – 0.415 (9.906 – 10.541) 0.165 – 0.180 (4.191 – 4.572) 0.045 – 0.055 (1.143 – 1.397) 15° TYP 0.060 (1.524) 0.183 (4.648) +0.008 0.004 –0.004 0.059 (1.499) TYP 0.330 – 0.370 (8.382 – 9.398) ( +0.203 0.102 –0.102 0.095 – 0.115 (2.413 – 2.921) 0.075 (1.905) 0.300 (7.
PAGE 16
LT1370 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1171 100kHz 2.5A Boost Switching Regulator Good for Up to VIN = 40V LTC 1265 12V 1.2A Monolithic Buck Converter Converts 5V to 3.3V at 1A with 90% Efficiency LT1302 Micropower 2A Boost Converter Converts 2V to 5V at 600mA in SO-8 Packages LT1372 500kHz 1.5A Boost Switching Regulator Also Regulates Negative Flyback Outputs LT1373 Low Supply Current 250kHz 1.