Datasheet

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LTC3803-5

38035fd

TYPICAL APPLICATION

DESCRIPTION

Constant Frequency

Current Mode Flyback

DC/DC Controller in ThinSOT

The LTC

3803-5 is a constant frequency current mode

ﬂ yback controller optimized for driving N-channel MOSFETs

in high input voltage applications. The LTC3803-5 operates

from inputs as low as 5V. Constant frequency operation

is maintained down to very light loads, resulting in less

low frequency noise generation over a wide range of load

currents. Slope compensation can be programmed with

an external resistor.

The LTC3803-5 provides ±1.5% output voltage accuracy

and consumes only 240μA of quiescent current. Ground-

referenced current sensing allows LTC3803-5-based con-

verters to accept input supplies beyond the LTC3803-5’s

absolute maximum V

. For simplicity, the LTC3803-5 can

be powered from a high V

through a resistor, due to its

internal shunt regulator. An internal undervoltage lockout

shuts down the IC when the input voltage is too low to

provide sufﬁ cient gate drive to the external MOSFET.

The LTC3803-5 is available in a low proﬁ le (1mm) 6-lead

SOT-23 (ThinSOT™) package.

Dual Output Wide Input Range Converter

FEATURES

APPLICATIONS

and V

OUT

Limited Only by External Components

4.8V Undervoltage Lockout Threshold

Operating Junction Temperature from –55°C to

150°C

Adjustable Slope Compensation

Internal Soft-Start

Constant Frequency 200kHz Operation

±1.5% Reference Accuracy

Current Mode Operation for Excellent Line and Load

Transient Response

No Minimum Load Requirement

Low Quiescent Current: 240μA

Low Proﬁ le (1mm) SOT-23 Package

42V and 12V Automotive Power Supplies

Telecom Power Supplies

Auxiliary/Housekeeping Power Supplies

Power Over Ethernet

Efﬁ ciency and Power Loss

vs Output Power

/RUN

GND

LTC3803-5

NGATE

SENSE

10MQ100N

B3100

1μF

100V

×3

13V/0.3A

20mA MIN

LOAD

6.5V/1.2A

38035 TA01

0.012Ω

0.1μF

22k

7.5k

57.6k

8.06k

4.7k

10nF

1μF

100V

1μF

100V

PHM25NQ10T

ALL CAPACITORS ARE X7R, TDK

6V TO 50V

MMBTA42

22μF

10V

47μF

10V

PDZ6.8B

VPH5-0155

OUTPUT POWER (W)

EFFICIENCY (%)

POWER LOSS (W)

3.0

2.5

2.0

1.5

1.0

0.5

6810

38035 TA01b

= 8V

= 12V

= 24V

= 48V

L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks

and ThinSOT and No R

SENSE

are trademarks of Linear Technology Corporation. All other

trademarks are the property of their respective owners.

Summary of content (16 pages)

PAGE 1
LTC3803-5 Constant Frequency Current Mode Flyback DC/DC Controller in ThinSOT FEATURES DESCRIPTION n The LTC®3803-5 is a constant frequency current mode ﬂyback controller optimized for driving N-channel MOSFETs in high input voltage applications. The LTC3803-5 operates from inputs as low as 5V. Constant frequency operation is maintained down to very light loads, resulting in less low frequency noise generation over a wide range of load currents.
PAGE 2
LTC3803-5 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) VCC to GND (Current Fed) ..................... 25mA into VCC* NGATE Voltage .......................................... – 0.3V to VCC VFB, ITH/RUN Voltages............................... –0.3V to 3.5V SENSE Voltage ............................................ –0.3V to 1V NGATE Peak Output Current (<10μs) ......................... 1A Operating Junction Temperature Range (Notes 2, 3) LTC3803E-5 .......................................
PAGE 3
LTC3803-5 ELECTRICAL CHARACTERISTICS The l denotes the speciﬁcations which apply over the full operating junction temperature range, otherwise speciﬁcations are at TA = 25°C. VCC = 5V, unless otherwise noted. (Notes 2, 3) SYMBOL PARAMETER CONDITIONS VCLAMP25mA VCC Shunt Regulator Voltage at 25mA ICC = 25mA, VITH/RUN = 0V LTC3803E-5 LTC3803I-5, LTC3803H-5 LTC3803MP-5 ICC ICC,(UV) VITHSHDN IITHSTART VFB l l l MIN TYP MAX UNITS 6.3 6.3 6 8.1 8.1 8.1 10.3 10.7 10.
PAGE 4
LTC3803-5 ELECTRICAL CHARACTERISTICS Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LTC3803-5 is tested under pulsed load conditions such that TJ ≈ TA. The LTC3803E-5 is guaranteed to meet speciﬁcations from 0°C to 85°C junction temperature.
PAGE 5
LTC3803-5 TYPICAL PERFORMANCE CHARACTERISTICS VCC Undervoltage Lockout Thresholds vs Temperature 10.5 5.5 10.0 300 VCC (V) VTURNON 4.0 9.0 ICC = 25mA 8.5 8.0 VTURNOFF ICC = 1mA 3.5 260 240 220 7.5 3.0 –60 –30 90 30 0 60 TEMPERATURE (°C) 120 7.
PAGE 6
LTC3803-5 PIN FUNCTIONS ITH/RUN (Pin 1): This pin performs two functions. It serves as the error ampliﬁer compensation point as well as the run/shutdown control input. Nominal voltage range is 0.7V to 1.9V. Forcing this pin below the shutdown threshold (VITHSHDN) causes the LTC3803-5 to shut down. In shutdown mode, the NGATE pin is held low. SENSE (Pin 4): This pin performs two functions. It monitors switch current by reading the voltage across an external current sense resistor to ground.
PAGE 7
LTC3803-5 OPERATION The LTC3803-5 is a constant frequency current mode controller for ﬂyback, SEPIC and DC/DC boost converter applications in a tiny ThinSOT package. The LTC3803-5 is designed so that none of its pins need to come in contact with the input or output voltages of the power supply circuit of which it is a part, allowing the conversion of voltages well beyond the LTC3803-5’s absolute maximum ratings.
PAGE 8
LTC3803-5 OPERATION The undervoltage lockout (UVLO) mechanism prevents the LTC3803-5 from trying to drive a MOSFET with insufﬁcient VGS. The voltage at the VCC pin must exceed VTURNON (nominally 4.8V) at least momentarily to enable LTC3803-5 operation. The VCC voltage is then allowed to fall to VTURNOFF (nominally 4V) before undervoltage lockout disables the LTC3803-5. The ITH/RUN pin can be driven below VITHSHDN (nominally 0.28V) to force the LTC3803-5 into shutdown. An internal 0.
PAGE 9
LTC3803-5 APPLICATIONS INFORMATION Many LTC3803-5 application circuits can be derived from the topology shown in Figure 2. The LTC3803-5 itself imposes no limits on allowed power output, input voltage VIN or desired regulated output voltage VOUT; these are all determined by the ratings on the external power components.
PAGE 10
LTC3803-5 APPLICATIONS INFORMATION 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. In some cases a “snubber” circuit will be required to avoid overvoltage breakdown at the MOSFET’s drain node. Application Note 19 is a good reference on snubber design.
PAGE 11
LTC3803-5 APPLICATIONS INFORMATION to duty cycle. This stabilizes the control loop against subharmonic oscillation. The amount of reduction in the current comparator threshold (ΔVSENSE) can be calculated using the following equation: ΔVSENSE = Duty Cycle – 6.5% • 5μA • RSL 73.5% Note: LTC3803-5 enforces 6.5% < Duty Cycle < 80%. A good starting value for RSL is 5.9k, which gives a 30mV drop in current comparator threshold at 80% duty cycle.
PAGE 12
LTC3803-5 TYPICAL APPLICATIONS 2W Isolated Housekeeping Telecom Converter BAS516 PRIMARY SIDE 10V, 100mA OUTPUT T1 220k • MMBTA42 2.2μF PDZ6.8B 130Ω 1μF VIN 36V TO 75V BAS516 • 9.09k 2.2μF BAS516 1k • SECONDARY SIDE 10V, 100mA OUTPUT SECONDARY SIDE GROUND 1nF 22k 787Ω 1 LTC3803-5 6 ITH/RUN NGATE 2 5 3 GND VFB VCC SENSE 4 FDC2512 T1: PULSE ENGINEERING PA0648 OR TYCO TTI8698 5.6k 1μF PRIMARY GROUND 0.
PAGE 13
LTC3803-5 TYPICAL APPLICATIONS 4:1 Input Range 3.3V Output Isolated Flyback DC/DC Converter T1 PA1277NL VIN+ 18 V TO 72V • 2.2μF 220k MMBTA42 GND BAS516 68Ω PDZ6.8B 100μF 6.3V ×3 PDS1040 • 150pF 130Ω VCC 10Ω 22Ω BAS516 680Ω • 1 2 3 ITH/RUN GATE 6 0.1μF FDC2512 LTC3803-5 5 VCC GND VFB SENSE 4 VOUT+ 4.7k 0.1μF BAT760 0.040Ω 270Ω VCC 1 6.8k BAS516 PS2801-1 0.1μF 1 2 0.33μF BAS516 2 3 VIN OPTO LT4430 GND OC COMP FB VOUT+ 6 2.2nF 5 56k 47pF 100k 4 22.
PAGE 14
LTC3803-5 PACKAGE DESCRIPTION S6 Package 6-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1636) 0.62 MAX 2.90 BSC (NOTE 4) 0.95 REF 1.22 REF 3.85 MAX 2.62 REF 1.4 MIN 2.80 BSC 1.50 – 1.75 (NOTE 4) PIN ONE ID RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.30 – 0.45 6 PLCS (NOTE 3) 0.95 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) 1.90 BSC S6 TSOT-23 0302 REV B NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3.
PAGE 15
LTC3803-5 REVISION HISTORY (Revision history begins at Rev D) REV DATE DESCRIPTION PAGE NUMBER D 6/10 MP-grade part added. Reﬂected throughout the data sheet. 1 to 16 38035fd Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
PAGE 16
LTC3803-5 TYPICAL APPLICATION Synchronous Flyback Converter VIN 36V TO 72V 220k MMBTA42 CIN • Q2 CO PDZ6.8B • 130Ω 1n VOUT* 3.3V 1.5A T1 D1 33k 1 8.06k ITH/RUN 6 GATE Q1 LTC3803-5 2 5 VCC GND 560 3 5k VFB SENSE 25.5k* RFB VOUT 4 1μF 10V T1: PULSE ENGINEERING PA1006 Q1: FAIRCHILD FDC2512 Q2: VISHAY Si9803 RCS • 0.1μF 38035 TA04 D1: PHILIPS BAS516 RCS: VISHAY OR IRC, 80mΩ CIN: TDK 1μF, 100V, X5R *FOR 5V OUTPUT CHANGE CO: TDK 100μF, 6.3V, X5R RFB TO 42.