Datasheet

ManualsBrandsLINEAR TECHNOLOGY ManualsPMICsPMIC - voltage regulators - DC DC switch controllers TSOT 23 8

LTC3873

3873fa

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

No R

SENSE

Constant

Frequency Current Mode

Boost/Flyback/SEPIC

DC/DC Controller

The LTC

3873 is a constant frequency current mode,

boost, ﬂ yback or SEPIC DC/DC controller that drives an

N-channel power MOSFET in high input and output volt-

age converter applications. Soft-start can be programmed

using an external capacitor.

The LTC3873 provides ±1.5% output voltage accuracy and

consumes only 300A quiescent current during normal

operation and only 55A during micropower start-up.

Using a 9.3V internal shunt regulator, the LTC3873 can

be powered from a high input voltage through a resistor

or it can be powered directly from a low impedance DC

voltage of 9V or less.

The LTC3873 is available in 8-lead ThinSOT and 2mm ×

3mm DFN packages.

and V

OUT

Limited Only by External Components

Internal or Programmable External Soft-Start

Constant Frequency 200kHz Operation

Adjustable Current Limit

Current Sense Resistor Optional

Maximum 60V on SW Node with R

DS(ON)

Sensing

±1.5% Voltage Reference Accuracy

Current Mode Operation for Excellent Line and Load

Transient Response

Low Quiescent Current: 300µA

Low Proﬁ le (1mm) ThinSOT

and (0.75mm)

2mm × 3mm DFN Package

Telecom Power Supplies

42V and 12V Automotive Power Supplies

Portable Electronic Equipment

Efﬁ ciency and Power Loss vs Load Current

5V Output Nonisolated Telecom Power Supply

PARAMETER LTC3873 LTC3873-5

8.4V 3.9V

–

4V 2.9V

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

No R

SENSE

and ThinSOT are trademarks of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

NGATE

LTC3873

RUN/SS

GND

0.1µF

100µF

6.3V

X5R

OUT

2A MAX

2.2nF

10µF

10V

X5R

4.7µF

100V

X5R

7.5k

221k

36V TO 72V

68m

3873 TA01a

•

IPRG

12.1k 38.3k

LOAD CURRENT (mA)

EFFICIENCY (%)

POWER LOSS (mW)

1000

3873 TA01b

100

EFFICIENCY

1000

500

2000

1500

2500

3000

POWER LOSS

= 72V

= 60V

= 48V

= 36V

Summary of content (16 pages)

PAGE 1
LTC3873 No RSENSETM Constant Frequency Current Mode Boost/Flyback/SEPIC DC/DC Controller FEATURES DESCRIPTION n The LTC®3873 is a constant frequency current mode, boost, ﬂyback or SEPIC DC/DC controller that drives an N-channel power MOSFET in high input and output voltage converter applications. Soft-start can be programmed using an external capacitor.
PAGE 2
LTC3873 ABSOLUTE MAXIMUM RATINGS (Note 1) VCC to GND Low Impedance Source ........................... –0.3V to 9V Current Fed ..........................................25mA Into VCC RUN/SS........................................................ –0.3V to 9V IPRG Voltage.................................–0.3V to (VCC + 0.3V) VFB, ITH Voltages ....................................... –0.3V to 2.4V SW Voltage ................................................ –0.3V to 60V Operating Temperature Range (Note 2)....
PAGE 3
LTC3873 ELECTRICAL CHARACTERISTICS The l denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. VCC = 9V unless otherwise noted. (Note 2) PARAMETER CONDITIONS MIN TYP MAX UNITS Input DC Supply Current Normal Operation Shutdown UVLO Typicals VITH = 1.9V VRUN/SS = 0V VCC = UVLO Threshold – 100mV, VRUN/SS = VCC 300 55 45 400 100 60 μA μA μA Undervoltage Lockout Threshold VCC Rising VCC Falling VCC Hysteresis l l l 7.9 3.5 4.
PAGE 4
LTC3873 TYPICAL PERFORMANCE CHARACTERISTICS Feedback Voltage vs Temperature Feedback Voltage Line Regulation 1.25 1.2025 1.24 1.2020 1.23 1.2015 ITH Voltage vs RUN/SS Voltage 2.5 VIN = 5V 1.22 1.21 ITH VOLTAGE (V) VFB VOLTAGE (V) VFB VOLTAGE (V) 2.0 1.2010 1.2005 1.20 1.2000 1.19 1.1995 1.5 1.0 0.5 1.18 –60 –40 –20 0 20 40 60 80 100 120 TEMPERATURE (°C) 1.
PAGE 5
LTC3873 TYPICAL PERFORMANCE CHARACTERISTICS Maximum Sense Threshold vs Temperature Frequency vs Temperature 300 MAXIMUM SENSE THRESHOLD (mV) 250 FREQUECY (kHz) 230 210 190 170 150 –60 –40 –20 0 20 40 60 80 100 120 TEMPERATURE (°C) 3873 G09 PIN FUNCTIONS IPRG = VIN 250 200 IPRG = FLOAT 150 IPRG = GND 100 50 0 –60 –40 –20 0 20 40 60 80 100 120 TEMPERATURE (°C) 3873 G10 (TS8/DDB) IPRG (Pin 1/Pin 4): Current Sense Limit Select Pin.
PAGE 6
LTC3873 FUNCTIONAL DIAGRAM GND VCC UV UNDERVOLTAGE LOCKOUT VOLTAGE REFERENCE 1.2V SW VCC 9.5V SHUNT REGULATOR SLOPE COMPENSATION SHUTDOWN COMPARATOR – + IPRG CURRENT COMPARATOR 3μA ILIM + SHDN ITH BUFFER RUN/SS RS LATCH – R S Q CURRENT LIMIT CLAMP VIN SWITCHING LOGIC CIRCUIT INTERNAL SOFT-START RAMP NGATE VFB – ERROR AMPLIFIER 200kHz OSCILLATOR AND MAX DUTY CYCLE 1.
PAGE 7
LTC3873 OPERATION Main Control Loop The LTC3873 is a general purpose N-channel switching DC/DC converter for boost, ﬂyback and SEPIC applications. Its No RSENSE sensing technique improves efﬁciency, increases power density and reduces the cost of the overall solution. For circuit operation, please refer to the Functional Diagram of the IC and the Typical Application on the front page.
PAGE 8
LTC3873 OPERATION (nominally 8.4V) at least momentarily to enable LTC3873 operation. The VCC voltage is then allowed to fall to VTURNOFF (nominally 4V) before undervoltage lockout disables the LTC3873. This wide UVLO hysteresis range supports the use of trickle charger on the ﬂyback transformer to power the LTC3873—see the section, VCC Bias Power. The RUN/SS pin can be driven below VSHDN (nominally 0.7V) to force the LTC3873 into shutdwn.
PAGE 9
LTC3873 APPLICATIONS INFORMATION VCC Bias Power The VCC pin must be bypassed to the GND pin with a minimum 10μF ceramic or tantalum capacitor located immediately adjacent to the two pins. Proper supply bypassing is necessary to supply the high transient currents required by the MOSFET gate driver. For maximum ﬂexibility, the LTC3873 is designed so that it can be operated from voltages well beyond the LTC3873’s absolute maximum ratings.
PAGE 10
LTC3873 APPLICATIONS INFORMATION The circuit in Figure 6 shows a third way to power the LTC3873. An external series pre-regulator consisting of series pass transistor Q1, zener diode D1 and bias resistor RB brings VCC to at least 7.6V nominal, well above the maximum rated VCC turn-off threshold of 4V. Resistor RSTART momentarily charges the VCC node up to the VCC turn-on threshold, enabling the LTC3873. VIN RB Q1 RSTART LTC3873 VCC D1 8.2V CVCC 0.
PAGE 11
LTC3873 APPLICATIONS INFORMATION plus the secondary-to-primary referred voltage of the ﬂyback pulse (including leakage spike) must not exceed the allowed external MOSFET breakdown rating. Leakage Inductance Transformer leakage inductance (on either the primary or secondary) causes a voltage spike to occur after the output switch (Q1) turn-off. This is increasingly prominent at higher load currents where more stored energy must be dissipated.
PAGE 12
LTC3873 APPLICATIONS INFORMATION In a ﬂyback converter, the input ﬂows in pulses placing severe demands on the input capacitors. Select an input capacitor with a ripple current rating greater than: IRMS = PIN VIN(MIN) 1 – DMAX DMAX impacted by duty factor. Unfortunately duty factor cannot be adjusted to simultaneously optimize all of these requirements. In general, avoid extreme duty factors since this severely impacts the current stress on most of the components.
PAGE 13
LTC3873 TYPICAL APPLICATIONS 9V to 15V VIN, 12V VOUT SEPIC Converter T1 4.56μH BH510-1009 BH ELECTRONICS 4 1 VIN 9V TO 15V 10μF s3 + 100μF 20V 2 • • 3 10μF 25V 301Ω UPS840 + LTC3873 100k 1 2 3 10nF 4 33.2k 11k IPRG ITH SW RUN/SS VFB = 1.2V VCC GND NGATE Si4840 8 47μF 16V s3 10μF 16V VOUT 12V 2A 7 6 5 4.7μF 0.1μF 3873 TA05 10W Isolated Telecom Converter TR1 ISOLATION BARRIER VIN 36V TO 72V 4.7μF 100V 221k OPT 221k MMBTA42 OPT PDZ6.
PAGE 14
LTC3873 PACKAGE DESCRIPTION TS8 Package 8-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1637) 0.52 MAX 2.90 BSC (NOTE 4) 0.65 REF 1.22 REF 1.4 MIN 3.85 MAX 2.62 REF 2.80 BSC 1.50 – 1.75 (NOTE 4) PIN ONE ID RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.22 – 0.36 8 PLCS (NOTE 3) 0.65 BSC 0.80 – 0.90 0.20 BSC 0.01 – 0.10 1.00 MAX DATUM ‘A’ 0.30 – 0.50 REF 0.09 – 0.20 (NOTE 3) 1.95 BSC TS8 TSOT-23 0802 NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3.
PAGE 15
LTC3873 PACKAGE DESCRIPTION DDB Package 8-Lead Plastic DFN (3mm × 2mm) (Reference LTC DWG # 05-08-1702 Rev B) 0.61 p0.05 (2 SIDES) 0.70 p0.05 2.55 p0.05 1.15 p0.05 PACKAGE OUTLINE 0.25 p 0.05 0.50 BSC 2.20 p0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 3.00 p0.10 (2 SIDES) R = 0.115 TYP 5 R = 0.05 TYP 0.40 p 0.10 8 2.00 p0.10 (2 SIDES) PIN 1 BAR TOP MARK (SEE NOTE 6) 0.56 p 0.05 (2 SIDES) 0.200 REF 0.75 p0.05 0 – 0.05 4 0.25 p 0.05 1 PIN 1 R = 0.20 OR 0.
PAGE 16
LTC3873 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT 1619 Current Mode PWM Controller 300kHz Fixed Frequency, Boost, SEPIC, Flyback Topology LTC1624 Current Mode DC/DC Controller SO-8; 300kHz Operating Frequency; Buck, Boost, SEPIC Design; VIN Up to 36V LTC1700 No RSENSE Synchronous Step-Up Controller Up to 95% Efﬁciency, Operating as Low as 0.