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FEATURES

n

LTC3788

2-Phase, Dual Output

Synchronous Boost Controller

DESCRIPTION

The LTC

®

3788 is a high performance 2-phase dual

synchronous boost converter controller that drives all

N-channel power MOSFETs. Synchronous rectiﬁcation

increases efﬁciency, reduces power losses and eases

thermal requirements, allowing the LTC3788 to be used

in high power boost applications.

A constant-frequency current mode architecture allows a

phase-lockable frequency of up to 850kHz. OPTI-LOOP

®

compensation allows the transient response to be optimized

over a wide range of output capacitance and ESR values.

The LTC3788 features a precision 1.2V reference and dual

power good output indicators. A 4.5V to 38V input supply

range encompasses a wide range of system architectures

and battery chemistries.

Independent SS pins for each controller ramp the output

voltages during start-up. The PLLIN/MODE pin selects

among Burst Mode

®

operation, pulse-skipping mode or

continuous inductor current mode at light loads.

For a leaded 28-lead SSOP package with a ﬁxed current

limit and one PGOOD output, without phase modulation

or a clock output, see the LTC3788-1 data sheet.

L,

LT, LTC, LTM, Linear Technology, Burst Mode, OPTI-LOOP PolyPhase and the Linear logo

,

are registered trademarks and No R

SENSE

and ThinSOT are trademarks of Linear Technology

Corporation. All other trademarks are the property of their respective owners. Protected by

U. S. Patents, including 5408150, 5481178, 5705919, 5929620, 6144194, 6177787, 6580258.

Synchronous Operation for Highest Efﬁciency and

Reduced Heat Dissipation

Wide Input Range: 4.5V to 38V (40V Abs Max) and

Operates Down to 2.5V After Start-Up

Output Voltages Up to 60V

±1% 1.2V Reference Voltage

R

SENSE

or Inductor DCR Current Sensing

100% Duty Cycle Capability for Synchronous MOSFET

Low Quiescent Current: 125μA

Phase-Lockable Frequency (75kHz to 850kHz)

Programmable Fixed Frequency (50kHz to 900kHz)

Selectable Current Limit

Adjustable Output Voltage Soft-Start

Power Good Output Voltage Monitors

Low Shutdown Current I

Q

: < 8μA

Internal LDO Powers Gate Drive from VBIAS or EXTV

CC

Thermally Enhanced Low Proﬁle 32-Pin 5mm × 5mm

QFN Package

APPLICATIONS

n

Industrial

Automotive

Medical

Military

TYPICAL APPLICATION

3mΩ

4.7μF

TG1 VBIAS INTV

CC

V

OUT

12V AT 5A

1.25μH

0.1μF

SW1

BG1

SENSE1

+

SENSE1

–

LTC3788

BOOST1

V

IN

4.5V TO 12V START-UP VOLTAGE

OPERATES THROUGH TRANSIENTS DOWN TO 2.5V

V

IN

4.7μF

TG2

Efﬁciency and Power Loss

vs Output Current

100

10000

90

4mΩ

220μF

BOOST2

SW2

BG2

SENSE2

+

SENSE2

–

PGND

3.3μH

0.1μF

V

OUT

24V AT 3A

EFFICIENCY (%)

80

70

60

50

40

30

1000

POWER LOSS (mW)

100

10

110k

VFB1

VFB2

FREQ

PLLIN/MODE

ITH1 SS1 SGND SS2 ITH2

220μF

12.1k

15nF

2.7k

100pF

0.1μF

220pF

0.1μF

15nF

8.66k

232k

V

IN

= 12V

1

V

OUT

= 24V

10

Burst Mode OPERATION

FIGURE 9 CIRCUIT

0.1

0

0.00001 0.0001 0.001 0.01

0.1

1

10

OUTPUT CURRENT (A)

20

220μF

3788 TA01b

12.1k

3788 TA01a

3788fa

1

LTC3788

ABSOLUTE MAXIMUM RATINGS

(Notes 1, 3)

PIN CONFIGURATION

TOP VIEW

SENSE1

+

PGOOD1

VBIAS......................................................... –0.3V to 40V

BOOST1, BOOST2 ...................................... –0.3V to 76V

SW1, SW2 ................................................. –0.3V to 70V

RUN1, RUN2 ................................................ –0.3V to 8V

Maximum Current Sourced into Pin

from Source > 8V..............................................100μA

PGOOD1, PGOOD2, PLLIN/MODE ............... –0.3V to 6V

INTV

CC

, (BOOST1-SW1, BOOST2-SW2) ...... –0.3V to 6V

EXTV

CC

......................................................... –0.3V to 6V

SENSE1

+

, SENSE1

–

,

SENSE2

+

, SENSE2

–

.................................... –0.3V to 40V

SENSE1

+

– SENSE1

–

,

SENSE2

+

– SENSE2

–

................................. –0.3V to 0.3V

I

LIM

, SS1, SS2, ITH1, ITH2, FREQ,

PHASMD, VFB1, VFB2 .......................... –0.3V to INTV

CC

Operating Junction Temperature Range ... –40°C to 125°C

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

VFB1

ITH1

SW1

SW2

ILIM

SS1

32 31 30 29 28 27 26 25

SENSE1

–

1

FREQ 2

PHASMD 3

CLKOUT 4

PLLIN/MODE 5

SGND 6

RUN1 7

RUN2 8

9 10 11 12 13 14 15 16

SENSE2

–

SENSE2

+

VFB2

ITH2

SS2

PGOOD2

TG2

33

GND

24 BOOST1

23 BG1

22 VBIAS

21 PGND

20 EXTV

CC

19 INTV

CC

18 BG2

17 BOOST2

UH PACKAGE

32-LEAD (5mm 5mm) PLASTIC QFN

T

JMAX

= 125°C,

θ

JA

= 34°C/W

EXPOSED PAD (PIN 33) IS GND, MUST BE SOLDERED TO PCB

ORDER INFORMATION

LEAD FREE FINISH

LTC3788EUH#PBF

LTC3788IUH#PBF

TAPE AND REEL

LTC3788EUH#TRPBF

LTC3788IUH#TRPBF

PART MARKING*

3788

PACKAGE DESCRIPTION

32-Lead (5mm

×

5mm) Plastic QFN

32-Lead (5mm

×

5mm) Plastic QFN

TEMPERATURE RANGE

–40°C to 125°C

Consult LTC Marketing for parts speciﬁed with wider operating temperature ranges. *The temperature grade is identiﬁed by a label on the shipping container.

Consult LTC Marketing for information on non-standard lead based ﬁnish parts.

For more information on lead free part marking, go to:

http://www.linear.com/leadfree/

For more information on tape and reel speciﬁcations, go to:

http://www.linear.com/tapeandreel/

ELECTRICAL CHARACTERISTICS

SYMBOL

VBIAS

V

FB1,2

I

FB1,2

V

REFLNREG

PARAMETER

Chip Bias Voltage Operating Range

Regulated Feedback Voltage

Feedback Current

Reference Line Voltage Regulation

Main Control Loop

The

l

denotes the speciﬁcations which apply over the full operating

junction temperature range, otherwise speciﬁcations are at T

A

= 25°C, VBIAS = 12V, unless otherwise noted (Note 2).

CONDITIONS

MIN

4.5

I

TH

= 1.2V (Note 4)

(Note 4)

VBIAS = 6V to 38V

l

TYP

TG1

MAX

38

UNITS

V

nA

%/V

1.188

1.200

±5

0.002

1.212

±50

0.02

3788fa

2

LTC3788

ELECTRICAL CHARACTERISTICS

SYMBOL

V

LOADREG

PARAMETER

Output Voltage Load Regulation

The

l

denotes the speciﬁcations which apply over the full operating

junction temperature range, otherwise speciﬁcations are at T

A

= 25°C, VBIAS = 12V, unless otherwise noted (Note 2).

CONDITIONS

(Note 4)

Measured in Servo Loop;

ΔI

TH

Voltage = 1.2V to 0.7V

Measured in Servo Loop;

ΔI

TH

Voltage = 1.2V to 2V

l

MIN

TYP

0.01

–0.01

2

0.9

1.2

125

200

8

MAX

0.1

–0.1

UNITS

%

mmho

mA

g

m1,2

I

Q

Error Ampliﬁer Transconductance

Input DC Supply Current

I

TH

= 1.2V

(Note 5)

Pulse-Skipping or Forced Continuous Mode RUN1 = 5V and RUN2 = 0V or RUN1 = 0V

(One Channel On)

and RUN2 = 5V; V

FB1(2)

= 1.25V (No Load)

Pulse-Skipping or Forced Continuous Mode RUN1,2 = 5V; V

FB1,2

= 1.25V (No Load)

(Both Channels On)

Sleep Mode

(One Channel On)

Sleep Mode

(Both Channels On)

Shutdown

UVLO

V

RUN1,2

V

RUNHYS

I

RUN1,2

I

RUN1,2

I

SS1,2

V

SENSE(MAX)

INTV

CC

Undervoltage Lockout Thresholds

RUN Pin On Threshold

RUN Pin Hysteresis

RUN Pin Hysteresis Current

RUN Pin Current

Soft-Start Charge Current

Maximum Current Sense Threshold

V

RUN

> 1.28V

V

RUN

< 1.28V

V

SS

= GND

V

FB

= 1.1V, I

LIM

= INTV

CC

V

FB

= 1.1V, I

LIM

= Float

V

FB

= 1.1V, I

LIM

= GND

V

SENSE(CM)

I

SENSE1,2+

I

SENSE1,2–

t

r(TG1,2)

t

f(TG1,2)

t

r(BG1,2)

t

f(BG1,2)

R

UP(TG1,2)

R

DN(TG1,2)

R

UP(TG1,2)

R

DN(TG1,2)

t

D(TG/BG)

t

D(BG/TG)

DF

MAX(BG1,2)

SENSE Pins Common Mode Range (BOOST

Converter Input Supply Voltage V

IN

)

SENSE

+

Pin Current

SENSE

–

Pin Current

Top Gate Rise Time

Top Gate Fall Time

Bottom Gate Rise Time

Bottom Gate Fall Time

Top Gate Pull-Up Resistance

Top Gate Pull-Down Resistance

Bottom Gate Pull-Up Resistance

Bottom Gate Pull-Down Resistance

Top Gate Off to Bottom Gate On

Switch-On Delay Time

Bottom Gate Off to Top Gate On

Switch-On Delay Time

Maximum BG Duty Factor

C

LOAD

= 3300pF (Each Driver)

C

LOAD

= 3300pF (Each Driver)

V

FB

= 1.1V, I

LIM

= Float

V

FB

= 1.1V, I

LIM

= Float

C

LOAD

= 3300pF (Note 6)

C

LOAD

= 3300pF (Note 6)

C

LOAD

= 3300pF (Note 6)

C

LOAD

= 3300pF (Note 6)

l

RUN1 = 5V and RUN2 = 0V or RUN1 = 0V

and RUN2 = 5V; V

FB1(2)

= 1.25V (No Load)

RUN1,2 = 5V; V

FB1,2

= 1.25V (No Load)

RUN1,2 = 0V

V

INTVCC

Ramping Up

V

INTVCC

Ramping Down

V

RUN

Rising

l

190

300

20

4.3

1.38

μA

V

mV

μA

4.1

3.6

1.18

3.8

1.28

100

4.5

0.5

7

90

68

42

2.5

200

20

1.2

70

96

10

100

75

50

13

110

82

56

38

300

±1

μA

mV

V

μA

ns

Ω

ns

%

3788fa

3

LTC3788

ELECTRICAL CHARACTERISTICS

SYMBOL

t

ON(MIN)

V

INTVCCVIN

V

LDOVIN

V

INTVCCEXT

V

LDOEXT

V

EXTVCC

V

LDOHYS

f

PROG

PARAMETER

Minimum BG On-Time

Internal V

CC

Voltage

INTV

CC

Load Regulation

Internal V

CC

Voltage

INTV

CC

Load Regulation

EXTV

CC

Switchover Voltage

EXTV

CC

Hysteresis

Programmable Frequency

R

FREQ

= 25k

R

FREQ

= 60k

R

FREQ

= 100k

f

LOW

f

HIGH

f

SYNC

V

PGL

I

PGOOD

V

PG

Lowest Fixed Frequency

Highest Fixed Frequency

Synchronizable Frequency

PGOOD Voltage Low

PGOOD Leakage Current

PGOOD Trip Level

V

FREQ

= 0V

V

FREQ

= INTV

CC

PLLIN/MODE = External Clock

I

PGOOD

= 2mA

V

PGOOD

= 5V

V

FB

with Respect to Set Regulated Voltage

V

FB

Ramping Negative

Hysteresis

V

FB

Ramping Positive

Hysteresis

t

PGOOD(DELAY)

I

BOOST1,2

PGOOD Delay

BOOST Charge Pump Available

Output Current

PGOOD Going High to Low

V

SW1,2

= 12V; V

BOOST1,2

– V

SW1,2

= 4.5V;

FREQ = 0V, Forced Continuous or

Pulse-Skipping Mode

BOOST1 and BOOST2 Charge Pump

55

μA

8

–12

–10

2.5

10

2.5

25

12

–8

%

μs

l

The

l

denotes the speciﬁcations which apply over the full operating

junction temperature range, otherwise speciﬁcations are at T

A

= 25°C, VBIAS = 12V, unless otherwise noted (Note 2).

CONDITIONS

(Note 7)

6V < VBIAS < 38V, V

EXTVCC

= 0V

I

CC

= 0mA to 50mA, V

EXTVCC

= 0V

V

EXTVCC

= 6V

I

CC

= 0mA to 40mA, V

EXTVCC

= 6V

EXTV

CC

Ramping Positive

4.5

5.2

MIN

TYP

110

5.4

0.5

5.4

0.5

4.8

250

105

335

320

485

75

0.2

400

760

350

535

380

585

850

0.4

±1

465

5.6

2

5.6

2

5

MAX

UNITS

ns

V

%

V

%

V

mV

kHz

V

μA

INTV

CC

Linear Regulator

Oscillator and Phase-Locked Loop

PGOOD1 and PGOOD2 Outputs

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 LTC3788 is tested under pulsed load conditions such that T

J

≈ T

A

. The LTC3788E is guaranteed to meet speciﬁcations from 0°C to 85°C

junction temperature. Speciﬁcations over the –40°C to 125°C operating

junction temperature range are assured by design, characterization and

correlation with statistical process controls. The LTC3788I is guaranteed

over the –40°C to 125°C operating junction temperature range. Note that

the maximum ambient temperature consistent with these speciﬁcations

is determined by speciﬁc operating conditions in conjunction with board

layout, the rated package thermal impedance and other environmental

factors. The junction temperature (T

J

, in °C) is calculated from the ambient

temperature (T

A

, in °C) and power dissipation (P

D

, in Watts) according to

the formula: T

J

= T

A

+ (P

D

•

θ

JA

), where

θ

JA

= 34°C/W.

Note 3:

This IC includes overtemperature protection that is intended to

protect the device during momentary overload conditions. The maximum

rated junction temperature will be exceeded when this protection is active.

Continuous operation above the speciﬁed absolute maximum operating

junction temperature may impair device reliability or permanently damage

the device.

Note 4:

The LTC3788 is tested in a feedback loop that servos V

FB

to the

output of the error ampliﬁer while maintaining I

TH

at the midpoint of the

current limit range.

Note 5:

Dynamic supply current is higher due to the gate charge being

delivered at the switching frequency.

Note 6:

Rise and fall times are measured using 10% and 90% levels.

Delay times are measured using 50% levels.

Note 7:

See Minimum On-Time Considerations in the Applications

Information section.

3788fa

4

LTC3788

TYPICAL PERFORMANCE CHARACTERISTICS

Efﬁciency and Power Loss

vs Output Current

100

90

80

EFFICIENCY (%)

70

60

50

40

30

20

10

0

0.01

V

IN

= 12V

V

OUT

= 24V

FIGURE 9 CIRCUIT

0.1

1

OUTPUT CURRENT (A)

BURST EFFICIENCY

PULSE-SKIPPING

EFFICIENCY

CCM EFFICIENCY

10

3788 G01

Efﬁciency and Power Loss

vs Output Current

10000

100

90

1000

POWER LOSS (mW)

EFFICIENCY (%)

80

70

60

50

40

30

V

IN

= 12V

1

V

OUT

= 24V

10

Burst Mode OPERATION

FIGURE 9 CIRCUIT

0.1

0

0.1

1

10

0.00001 0.0001 0.001 0.01

OUTPUT CURRENT (A)

20

3788 G02

10000

1000

POWER LOSS (mW)

100

10

1

0.1

BURST LOSS

PULSE-SKIPPING

LOSS

CCM LOSS

BURST EFFICIENCY

BURST LOSS

Efﬁciency vs Input Voltage

100

99

98

EFFICIENCY (%)

97

96

95

94

93

92

91

90

0

5

15

10

INPUT VOLTAGE (V)

20

25

3788 G03

Load Step

Forced Continuous Mode

LOAD STEP

2A/DIV

I

LOAD

= 2A

FIGURE 9 CIRCUIT

V

OUT

= 12V

V

OUT

= 24V

INDUCTOR

CURRENT

5A/DIV

V

OUT

500mV/DIV

200μs/DIV

V

IN

= 12V

V

OUT

= 24V

FIGURE 9 CIRCUIT

3788 G04

Load Step

Burst Mode Operation

LOAD STEP

2A/DIV

INDUCTOR

CURRENT

5A/DIV

LOAD STEP

2A/DIV

INDUCTOR

CURRENT

5A/DIV

Load Step

Pulse-Skipping Mode

V

OUT

500mV/DIV

V

OUT

500mV/DIV

200μs/DIV

V

IN

= 12V

V

OUT

= 24V

FIGURE 9 CIRCUIT

3788 G05

200μs/DIV

V

IN

= 12V

V

OUT

= 24V

FIGURE 9 CIRCUIT

3788 G06

3788fa

5

LTC3788

LTC3788概述

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