Datasheet

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LT1339

sn1339 1339fas

High Power Synchronous

DC/DC Controller

DESCRIPTION

FEATURES

The LT

1339 is a high power synchronous current mode

switching regulator controller. The IC drives dual

N-channel MOSFETs to create a single IC solution for high

power DC/DC converters in applications up to 60V.

The LT1339 incorporates programmable average current

limiting, allowing accurate limiting of DC load current

independent of inductor ripple current. The IC also incor-

porates user-adjustable slope compensation for minimi-

zation of magnetics at duty cycles up to 90%.

The LT1339 timing oscillator operating frequency is pro-

grammable and can be synchronized up to 150kHz. Mini-

mum off-time operation provides main switch protection.

The IC also incorporates a soft start feature that is gated by

both shutdown and undervoltage lockout conditions.

An output phase reversal pin allows flexibility in configu-

ration of converter types, including inverting and negative

topologies.

■

High Voltage: Operation Up to 60V

■

High Current: Dual N-Channel Synchronous Drive

Handles Up to 10,000pF Gate Capacitance

■

Programmable Average Load Current Limiting

■

5V Reference Output with 10mA External

Loading Capability

■

Programmable Fixed Frequency Synchronizable

Current Mode Operation Up to 150kHz

■

Undervoltage Lockout with Hysteresis

■

Programmable Start Inhibit for Power Supply

Sequencing and Protection

■

Adaptive Nonoverlapping Gate Drive Prevents

Shoot-Through

■

48V Telecom Power Supplies

■

Personal Computers and Peripherals

■

Distributed Power Converters

■

Industrial Control Systems

■

Lead-Acid Battery Backup Systems

■

Automotive and Heavy Equipment

APPLICATIONS

TYPICAL APPLICATION

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

28V to 5V 20A Buck Converter

SYNC V

BOOST

REF

CT TS

SL/ADJ

12V

AVG

PGND

PHASE

SGND

RUN/SHDN

SENSE

REF

SENSE

–

DBST

IN5819

12V

28V

1500µF

63V

× 3

IRL3803

IRL3103D2

× 2

10µH

OUT

5V AT 20A

FB2

FB1

LT1339

CBST

1µF

12VIN

47µF

OUT

2200µF

6.3V

× 2

MBR0520

RUN

100k

0.005Ω

10k

2200pF

AVG

2200pF

1µF

1nF

, 10k

REF

0.1µF

1339 TA03

L1 = CTX02-13400-X2

5VREF

1µF

28V to 5V Efficiency

OUTPUT CURRENT (A)

EFFICIENCY (%)

1339 TA03a

100

Summary of content (20 pages)

PAGE 1
LT1339 High Power Synchronous DC/DC Controller U DESCRIPTION FEATURES ■ ■ ■ ■ ■ ■ ■ ■ The LT ®1339 is a high power synchronous current mode switching regulator controller. The IC drives dual N-channel MOSFETs to create a single IC solution for high power DC/DC converters in applications up to 60V.
PAGE 2
LT1339 U U RATI GS W W W W AXI U U ABSOLUTE PACKAGE/ORDER I FOR ATIO (Note 1) Supply Voltages Power Supply Voltage (12VIN)...............– 0.3V to 20V Topside Supply Voltage (VBOOST) VTS – 0.3V to VTS + 20V (VMAX = 75V) Topside Reference Pin Voltage (TS) ......– 0.3V to 60V Input Voltages Sense Amplifier Input Common Mode ...– 0.3V to 60V RUN/SHDN Pin Voltage ...................... – 0.3V to 12VIN All Other Inputs .......................................– 0.
PAGE 3
LT1339 ELECTRICAL CHARACTERISTICS 12VIN = VBOOST = 12V, VC = 2V, TS = 0V, VFB = VREF = 1.25V, CTG = CBG = 3000pF, TA = 25°C unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS ● 1.242 1.235 1.250 1.250 1.258 1.265 V V ● 0.1 0.5 1.
PAGE 4
LT1339 U W TYPICAL PERFORMANCE CHARACTERISTICS Boost Supply Current vs Temperature 12VIN Supply Current vs Temperature 5V REFERENCE SHORT-CIRCUIT CURRENT (mA) 18 17 3.5 I12VIN SUPPLY CURRENT (mA) BOOST SUPPLY CURRENT (mA) 4.0 3.0 2.5 2.0 1.5 16 15 14 13 12 11 1.0 –50 –25 50 25 75 0 TEMPERATURE (°C) 100 10 –50 –25 125 0 25 50 75 125 55 50 45 40 35 30 –50 –25 180 1.251 160 150 125 5V Reference Voltage vs Temperature 5.01 5V REFERENCE VOLTAGE (V) 1.
PAGE 5
LT1339 U W TYPICAL PERFORMANCE CHARACTERISTICS Soft Start Charge Current vs Temperature RUN/SHDN Rising Threshold vs Temperature 8 7 6 –50 –25 50 25 75 0 TEMPERATURE (°C) 100 26 RUN/SHDN THRESHOLD HYSTERESIS (mV) 1.26 RUN/SHDN RISING THRESHOLD (V) SOFT START CHARGE CURRENT (µA) 9 1.25 1.24 1.23 1.22 1.21 1.
PAGE 6
LT1339 U W TYPICAL PERFORMANCE CHARACTERISTICS Sense Amplifier Input Bias Current (Source) vs Temperature UVLO Thresholds vs Temperature 10.00 1200 9.75 1100 RISING FALLING 8.75 900 800 700 8.50 600 8.25 500 25 0 75 50 0 25 50 75 100 600 500 UPPER LIMIT 300 200 100 0 600 TYPICAL LOWER LIMIT 1.0 (1.25) 1.5 2.0 0.5 RUN/SHDN INPUT VOLTAGE (V) FULL OPERATING TEMPERATURE RANGE 450 TYPICAL LOWER LIMIT 150 0 2.
PAGE 7
LT1339 U U U PIN FUNCTIONS SYNC (Pin 1): Oscillator Synchronization Pin with TTLLevel Compatible Input. Input drives internal rising edge triggered one-shot; sync signal on/off times should be ≥1µs (10% to 90% DC at 100kHz). Does not contain internal pull-up. Connect to SGND if not used. 5VREF (Pin 2): 5V Output Reference. Allows connection of external loads up to 10mA DC. (Reference is not available in shutdown.) Typically bypassed with 1µF capacitor to SGND. CT (Pin 3): Oscillator Timing Pin.
PAGE 8
LT1339 W FU CTIO AL BLOCK DIAGRA U U VIN VBOOST MAIN SWITCH CT PHASE 12VIN 5VREF TG TS NONOVERLAPPING SWITCH LOGIC BG Q SYNC SWITCH S UVLO CIRCUIT R OSC SL/ADJ ONE SHOT SENSE + RSENSE VOUT + × 15 SENSE – + SYNC + – IC1 CURRENT SENSE AMP 0.5µA – – VFB VC EA + VREF 1.25V 5VREF 2.5V 5V – 8µA REFERENCE 50k SOFT START + + RUN/SHDN AVERAGE CURRENT LIMIT CIRCUIT ENABLE 1.
PAGE 9
LT1339 U OPERATION (Refer to Functional Block Diagram) The current comparator trip threshold is set on the VC pin, which is the output of a transconductance amplifier, or error amplifier (EA). The error amplifier integrates the difference between a feedback voltage (on the VFB pin) and an internal bandgap generated reference voltage of 1.25V, forming a signal that represents required load current.
PAGE 10
LT1339 U U W U APPLICATIONS INFORMATION RSENSE generates a voltage that is proportional to the inductor current for use by the LT1339 current sense amplifier. The value of RSENSE is based on the required load current. The average current limit function has a typical threshold of 120mV/RSENSE, or: RSENSE = 120mV/ILIMIT Operation with VSENSE common mode voltage below 4.5V may slightly degrade current limit accuracy.
PAGE 11
LT1339 U W U U APPLICATIONS INFORMATION impedance of the IAVG pin. The integrator corner frequency is typically set 1 to 2 orders of magnitude below the oscillator frequency and follows the relation: f–3dB = (3.2)(10– 6)/CAVG The average current limit function can be disabled by shorting the IAVG pin directly to SGND. Soft Start Programming The current control pin (VC) limits sensed inductor current to zero at voltages less than a transistor VBE, to full average current limit at VC = VBE + 1.8V.
PAGE 12
LT1339 U W U U APPLICATIONS INFORMATION the converter input supply is enabled with no voltage on the LT1339 12VIN pin, the LT1339 driver output clamps will not be activated. To prevent turn-on, an external current path must be used to bleed off charge on the switch MOSFET gates. High value bleed resistors (50k to 250k) should be connected between the TG and SW pins and between BG and PGND. This provides discharge paths for the switch MOSFET gates, preventing parasitic turn-on and damage to the MOSFETs.
PAGE 13
LT1339 U U W U APPLICATIONS INFORMATION Subharmonic oscillations can be eliminated by augmenting the increasing ripple current slope (S1) in the control loop. This is accomplished by adding an artificial ramp on the inductor current waveform internal to the IC (with a slope SX) as shown in Figure 5b. If the sum of the slopes S1 + SX is greater than S2, the condition for subharmonic oscillation no longer exists.
PAGE 14
LT1339 U W U U APPLICATIONS INFORMATION 2 further increasing the effective compensation slope up to 20% for a given setting. Design Example: VIN = 20V VOUT = 15V (DC = 0.75) RSENSE = 0.01Ω fO = 100kHz L = 5µH ) () 1339 • F07a 2V 0.8V DC = 0.75 (0.084 + 0.139)(fO) RSENSE (0.084)(fO) RSENSE Amp/s Subtracting the internally generated slope compensation and solving for the required effective resistance at SL/ADJ yields: REQ ≤ SL/ADJ 2.
PAGE 15
LT1339 U W U U APPLICATIONS INFORMATION In high voltage applications (VIN > 20V), the topside switch is required to slew very large voltages. As VIN increases, transition losses increase through a square relation, until it becomes the dominant power loss term in the main switch. This transition loss takes the form: PTR ≈ (k)(VIN)2(IMAX)(CRSS)(fO) where k is a constant inversely related to the gate drive current, approximated by k = 2 in LT1339 applications.
PAGE 16
LT1339 U W U U APPLICATIONS INFORMATION is also small. However, since the FET gate must switch up past the 48V input voltage, transition loss can become a significant factor. In such a case, it is often prudent to take the increased I2R loss of a smaller FET in order to reduce CRSS and thus, the associated transition losses. Gate Drive Buffers The LT1339 is designed to drive relatively large capacitive loads.
PAGE 17
C11 0.1µF + + C12 100pF + C10 0.1µF C9 1800pF 5% NPO + + + + C14 3300pF R9 12k C1: SANYO 63MV680GX C2: WIMA SMD4036/1.5/63/20/TR C6: KEMET T510X477M006AS (X8) L1: GOWANDA 50-318 T1: GOWANDA 50-319 + R5 2.49k 1% 12V VIN 48V 10 7 6 5 3 4 2 1 17 C15 0.1µF 8 SGND VREF VC SS IAVG CT 11 18 19 20 15 PGND 12 SENSE – 16 BG 14 PHASE 13 RUN/SHDN 9 VFB SENSE + TS TG 5VREF SL/ADJ VBOOST SYNC D2 MURS120 C2 1.
PAGE 18
C1 1.2µF 100V CER 68µF 20V AVX TSPE 10k P + 100k 0.1µF P 3.9k GND1 IN1 PHASE JP3 W2 T1 2 W3 2 7 5 6 18 1 RUN/SHDN 12VIN 20 2.2µF 19 OUT1 VCC1 470Ω OUT2 IN2 VCC2 LTC1693-1 GND2 JP2 100k 14 13 17 1 8 3 4 12V 5VOUT SHORT JP3, OPEN JP2 3.3VOUT, SHORT JP2, OPEN JP3 BAS21 BAS21 BAS21 13k MMBD914LT1 C2 1.
PAGE 19
LT1339 U TYPICAL APPLICATIONS 5V to 28V DC/DC Synchronous Boost Converter Limits Input Current at 60A (DC) 12V + DBST MBR0530 VBOOST SYNC + C5VREF Q2 FMMT720 TG CT TS 12VIN SL/ADJ CCT CAVG 2200pF 2200pF 12L + CVC, 1500pF VFB CREF, 0.1µF RR1 100k PHASE RUN/SHDN SENSE – VREF RFB2, 1.2k D2 MBR0520 L1 40µH PGND SGND RFB1, 27k Q4 FMMT720 BG VC RVC, 7.
PAGE 20
LT1339 U TYPICAL APPLICATION 48V to 5V 50A DC/DC Converter with Input Supply Start-Up Protection 12V RCT 10k 5VREF VBOOST VIN 48V + DBST IN5819 LT1339 SYNC 50mA C12VIN 47µF Q1 + CBST CT + CCT TG CAVG, 2200pF CSS, 10µF CVC, 2200pF D3 MMSZ4684 12VIN CBG, 1µF IAVG SS PGND RFB2 1k RFB1 3k RR1 22k RR3 51k PHASE SGND RUN/SHDN VFB VREF D2 MBR0520 Q4 RVC, 4.7k CREF 0.