LINEAR TECHNOLOGY LTC3806 Technical data

查询LTC3806供应商

FEATURES

■

High Efficiency at Full Load

■

Better Cross Regulation Than Nonsynchronous
Converters (Multiple Outputs)

■

Soft-Start Minimizes Inrush Current

■

Current Mode Control Provides Excellent
Transient Response

■

High Maximum Duty Cycle: 89% Typical

■

±2% Programmable Undervoltage Lockout Threshold

■

±1% Internal Voltage Reference

■

Micropower Start-Up

■

Constant Frequency Operation (Never Audible)

■

3mm × 4mm 12-Pin DFN Package

LTC3806

Synchronous

Flyback DC/DC Controller

U

DESCRIPTIO

The LTC®3806 is a current mode synchronous flyback
controller that drives N-channel power MOSFETs and
requires very few external components. It is intended for
medium power applications where multiple outputs are
required. Synchronous rectification provides higher effi­ciency and improved output cross regulation than
nonsynchronous converters.

The IC contains all the necessary control circuitry includ­ing a 250kHz oscillator, precision undervoltage lockout
circuit with hysteresis, gate drivers for primary and syn­chronous switches, current mode control circuitry and
soft-start circuitry.

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APPLICATIO S

■

48V Telecom Supplies

■

12V/42V Automotive

■

24V Industrial

■

VoIP Phone

■

Power Over Ethernet

TYPICAL APPLICATIO

V

IN

36V TO 72V

604k

C1
100µF

R2

R8
100Ω

R3

26.7k

51k

R1

R4

3.4k

C2
1nF

U

C7

4.7µF

RUN
I

TH

FB
V

IN

INTV

C3

4.7µF

LTC3806

SENSE

CC

GND

Programmable soft-start reduces inrush currents. This
makes it easier to design compliant Power Over Ethernet
supplies.

Low start-up current reduces power dissipation in the
start-up resistor and reduces the size of the external start­up capacitor.

The LTC3806 is available in a 12-pin, exposed pad DFN
package.

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

V

OUT1

3.3V

V

3A

C6
470µF

OUT2

2.5V
3A

D1

SS
G2
G1

T1

•

••

M1 M2 M3

C4

0.47µF

R5

0.056Ω

C5
470µF

R7

12.4k

R6

21k

Figure 1. Multiple Output Flyback Converter for Telecom

3806 F01

3806f

1

LTC3806

12
11
10

9
8
7

1
2
3
4
5
6

SENSE
NC
SS
G1
G2
GND

RUN

I

TH

FB
NC
V

IN

INTV

CC

TOP VIEW

13

DE12 PACKAGE

12-LEAD (4mm × 3mm) PLASTIC DFN

ABSOLUTE MAXIMUM RATINGS

(Note 1)

VIN Voltage ............................................................. 25V

INTVCC Voltage ......................................................... 8V

INTVCC Output Current ........................................ 50mA

G1, G2 Voltages....................... –0.3V to V

ITH, FB, SS Voltages .................................–0.3V to 2.7V

RUN Voltage ............................................... –0.3V to 7V

SENSE Pin Voltage ..................................... –0.3V to 8V

Operating Ambient Temperature Range

(Note 2) .................................................. – 40°C to 85°C

Junction Temperature (Note 3)............................ 125°C

Storage Temperature Range ................. –65°C to 125°C

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are TA = 25°C. VIN = 10V, V

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Main Control Loop

V

IN(MIN)

I

Q

+

V

RUN

–

V

RUN

V

RUN(HYST)

I

RUN

V

FB

I

FB

∆VFB/∆VINLine Regulation 10V ≤ VIN ≤ 20V 0.01 %/V
∆VFB/∆V

g

m

V

SENSE(MAX)

I

SENSE(ON)

I

SENSE(OFF)

I

SS

Oscillator

f

OSC

DC(MAX) Maximum Duty Cycle 84 89 94 %

2

Minimum Input Voltage (Note 4) 10 V
Input Voltage Supply Current (Note 5)

Quiescent 1000 µA
Shutdown Mode V
Start-Up Mode V

Rising RUN Input Threshold Voltage VIN = 20V 1.205 1.230 1.255 V

Falling RUN Input Threshold Voltage VIN = 20V 1.116 1.139 1.162 V

RUN Pin Input Threshold Hysteresis VIN = 20V 45 91 137 mV
RUN Input Current 160 nA
Feedback Voltage V

Feedback Pin Input Current V

Load Regulation VTH = 0.55V to 0.95V (Note 6) ● –1 –0.1 %

ITH

Error Amplifier Transconductance ITH Pin Load = ±5µA (Note 6) 650 µMho
Maximum Current Sense Input Threshold 110 150 190 mV
SENSE Pin Current (G1 High) V
SENSE Pin Current (G1 Low) V
SS Pin Source Current VSS = 1.5V 3 5 8 µA

Oscillator Frequency 210 250 290 kHz

WW

W

U

INTVCC

+ 0.3V

The ● denotes specifications which apply over the full operating

= 0V 50 90 µA

RUN

> 1.255V, VIN < 7V 80 140 µA

RUN

= 0.75V (Note 6) 1.218 1.230 1.242 V

ITH

= 0.75V (Note 6) 18 100 nA

ITH

= 0V 35 50 µA

SENSE

= 1V 0.1 5 µA

SENSE

U

W

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PACKAGE/ORDER INFORMATION

ORDER PART

NUMBER

LTC3806EDE

DE PART MARKING

3806

T

= 125°C, θJA = 34°C/W

JMAX

EXPOSED PAD (PIN 13) IS GND

MUST BE SOLDERED TO PCB

Consult LTC Marketing for parts specified with wider operating temperature ranges.

= 1.5V, unless otherwise specified.

RUN

● 1.181 1.279 V

● 1.093 1.185 V

● 1.212 1.248 V

3806f

LTC3806

TEMPERATURE (°C)

–40

0

FB PIN CURRENT (nA)

5

10

15

20

25

30

–15 10 35 60

3806 G03

85

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are TA = 25°C. VIN = 10V, V

The ● denotes specifications which apply over the full operating

= 1.5V, unless otherwise specified.

RUN

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Regulator

V

INTVCC

∆INTV
∆V

IN

V

LDO(LOAD)

+

V

UVL

–

V

UVL

INTVCC Regulator Output Voltage VIN = 10V 6 6.9 7.8 V
INTVCC Regulator Line Regulation 10V ≤ VIN ≤ 20V 100 mV

CC

INTVCC Load Regulation 0 ≤ I

≤ 20mA –6 –3 %

INTVCC

Rising VIN Threshold Voltage 14 15 16 V
Falling VIN Threshold Voltage 7.5 8 8.5 V

Gate Drivers

t

r1

t

f1

t

r2

t

f2

t

DEAD

Note 1: Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.

Note 2: The LTC3806E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.

Note 3: T
dissipation P

TJ = TA + (PD • 34°C/W)

Gate Driver 1 Output Rise Time CL1 = 3300pF 25 100 ns
Gate Driver 1 Output Fall Time CL1 = 3300pF 18 100 ns
Gate Driver 2 Output Rise Time CL2 = 4700pF 25 100 ns
Gate Driver 2 Output Fall Time CL2 = 4700pF 18 100 ns
Gate Driver Dead Time CL1 = 3300pF, CL2 = 4700pF 100 ns

Note 4: The minimum operating voltage is allowed once operation begins.
To begin operation, V
threshold with V

must be above the rising undervoltage lockout

IN

above the rising RUN input threshold.

RUN

Note 5: The dynamic input supply current is higher due to power MOSFET

• f

gate charging (Q

). See Applications Information.

G

OSC

Note 6: The LTC3806 is tested in a feedback loop which servos VFB to the

is calculated from the ambient temperature TA and power

J

according to the following formula:

D

reference voltage with the I
(the no load to full load operating voltage range for the I

pin forced to a voltage between 0V and 1.4V

TH

pin is 0.3V to

TH

1.23V).

TYPICAL PERFOR A CE CHARACTERISTICS

1.2400

1.2350

1.2300

1.2250

FB VOLTAGE (V)

1.2200

1.2150

UW

FB Voltage vs Temperature FB Voltage Line Regulation FB Pin Current vs Temperature

1.2310
TA = 25°C

1.2305

1.2300

FB VOLTAGE (V)

1.2295

–40

–15

10

TEMPERATURE (°C)

35

60

3806 G01

1.2290

85

11

12

10

15

16

17

18

19

13

14

VIN (V)

20

3806 G02

3806f

3

LTC3806

TEMPERATURE (°C)

–40

1.10

RUN THRESHOLDS (V)

1.12

1.14

1.16

1.18

1.20

1.22
TRIP

–15 10 35 60

3806 G10

85

RELEASE

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Shutdown Mode IQ vs V

80

TA = 25°C

70

60

(µA)

Q

50

40

30

20

SHUTDOWN MODE, I

10

0

4 8 12 20142 6 10 18

0

VIN (V)

G1 Rise and Fall Time vs C

250

TA = 25°C

200

150

TIME (ns)

100

Shutdown Mode I

IN

16

3806 G04

L

vs Temperature Soft-Start Current vs Temperature

80

75

(µA)

Q

70

65

60

SHUTDOWN MODE, I

55

50

–40

–15 10 35 60

G2 Rise and Fall Time vs C

120

TA = 25°C

100

80

60

TIME (ns)

40

Q

TEMPERATURE (°C)

7.0

6.5

6.0

5.5

SOFT-START CURRENT (µA)

85

3806 G05

L

5.0
–40

–15 10 35 60

TEMPERATURE (°C)

RUN Thresholds vs Temperature

85

3806 G06

50

0

20

4000

0

8000

CL (pF)

12000

16000

20000

3806 G07

0

4000

0

8000

12000

16000

20000

C

(pF)

L

3806 G08

Maximum Sense Threshold

Frequency vs Temperature

260

255

250

FREQUENCY (kHz)

245

240

–40

–15

10

TEMPERATURE (°C)

35

60

85

3806 G11

vs Temperature

155
154
153
152
151
150
149
148
147

MAX SENSE THRESHOLD (mV)

146
145

–40

–15

10

TEMPERATURE (°C)

35

60

85

3806 G12

3806f

4

UW

VIN (V)

10

6.990

INTV

CC

VOLTAGE (V)

6.995

7.000

7.005

7.010

7.015

7.020

12 14 16 18

3806 G15

20

TYPICAL PERFOR A CE CHARACTERISTICS

SENSE Pin Current
vs Temperature INTVCC Load Regulation INTVCC Line Regulation

32.0

31.5

7.020

7.015

7.010

TA = 25°C

LTC3806

SENSE PIN CURRENT (µA)

31.0

30.5

30.0
–40

–15

10

TEMPERATURE (°C)

2.8

2.7

2.6

2.5

2.4

2.3

2.2

DROPOUT VOLTAGE (V)

2.1

2.0

1.9

35

60

85

3806 G13

INTVCC Dropout Voltage
vs Current, Temperature

TA = –40°C

TA = 0°C

TA = 25°C

TA = 55°C

TA = 85°C

0

10 30

20

INTVCC LOAD (mA)

7.005

VOLTAGE (V)

CC

7.000

INTV

6.995

6.990
0

40

3806 G16

10 20 30 40

INTVCC LOAD (mA)

50

50

3806 G14

Efficiency vs Output Power

90

FIGURE 8 CIRCUIT

85

EFFICIENCY (%)

80

75

30 50 70 90

% OF MAXIMUM OUTPUT POWER

1002010 40 60 80

3806 G17

3806f

5

LTC3806

U

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PI FU CTIO S

RUN (Pin 1): The RUN pin provides the user with an
accurate means for sensing the input voltage and pro­gramming the start-up threshold for the converter. The
falling RUN pin threshold is nominally 1.14V and the
comparator has 91mV of hysteresis for noise immunity.
When the RUN pin is below this input threshold, the gate
drive outputs G1 and G2 are held low. The absolute
maximum rating for the voltage on this pin is 7V.

ITH (Pin 2): Error Amplifier Compensation Pin. The current
comparator input threshold increases with this control
voltage. Nominal voltage range for this pin is 0V to 1.4V.

FB (Pin 3): Receives the feedback voltage from the exter­nal resistor divider across the main output. Nominal
voltage for this pin in regulation is 1.230V.

NC (Pins 4, 11): Do Not Connect.
VIN (Pin 5): Main Supply Pin. Must be closely decoupled

to ground.

INTV

gate drivers and control circuits are powered from this
voltage. Decouple this pin locally to the IC ground with a
minimum 4.7µF low ESR ceramic capacitor.

GND (Pins 7, 13): Ground Pins. Exposed pad must be tied
to electrical ground.

G2 (Pin 8): Secondary-Side Gate Driver Output. This pin
drives the gates of all of the synchronous rectifiers.

G1 (Pin 9): Primary-Side Gate Driver Output.
SS (Pin 10): Soft-Start. A capacitor between this pin and

ground sets the rate at which the current comparator input
threshold may increase when the IC is initially enabled.
Increasing the size of the capacitor slows down the ramp
rate and reduces the inrush current.

SENSE (Pin 12): Current Sense Input for the Control Loop.
Connect this pin to the current sense resistor in the source
of the primary side power MOSFET. Internal leading edge
blanking is provided.

(Pin 6): The Internal 6.9V Regulator Output. The

CC

6

3806f