LINEAR TECHNOLOGY LTC3709 Technical data

LTC3709

FEATURES

■

PolyPhase® Valley Current Mode Controller

■

Synchronizable to an External Clock with PLL

■

Coincident or Ratiometric Tracking

■

Sense Resistor Optional

■

2% to 90% Duty Cycle at 200kHz

■

t

ON(MIN)

■

True Remote Sensing Differential Amplifier

■

High Efficiency at Both Light and Heavy Loads

■

Power Good Output Voltage Monitor

■

0.6V ±1% Reference

■

Adjustable Current Limit

■

Programmable Soft-Start and Operating Frequency

■

Output Overvoltage Protection

■

Optional Short-Circuit Shutdown Timer

■

Available in 32-Lead (5mm × 5mm) QFN and 36-Lead

< 100ns

SSOP Packages

U

APPLICATIO S

■

Notebook Computers

■

Power Supply for DSP, ASIC, Graphic Processors

Fast 2-Phase, No R

SENSE

Synchronous DC/DC Controller

with Tracking/Sequencing

U

DESCRIPTIO

The LTC®3709 is a single output, dual phase, synchronous
step-down switching regulator. The controller uses a
constant on-time, valley current control architecture to
deliver very low duty cycles without requiring a sense
resistor. Operating frequency is selected by an external
resistor and is compensated for variations in input supply
voltage. An internal phase-lock loop allows the LTC3709
to be synchronized to an external clock.

A TRACK pin is provided for tracking or sequencing the
output voltage among several LTC3709 chips or an
LTC3709 and other DC/DC regulators. Soft-start is ac­complished using an external timing capacitor.

Fault protection is provided by an output overvoltage com­parator and an optional short-circuit shutdown timer. The
current limit level is user programmable. A wide supply
range allows voltages as high as 31V to step down as low
as 0.6V.

TM

, LTC and LT are registered trademarks of Linear Technology Corporation. No R
a trademark of Linear Technology Corporation. PolyPhase is a registered trademark of
Linear Technology Corporation. All other trademarks are the property of their respective
owners. Protected by U.S. Patents including 5481178, 6476589, 6144194, 5847554,
6177678, 6304066, 6580258, 6674274, 6462525, 6593724.

SENSE

,

is

TYPICAL APPLICATIO

High Efficiency Dual Phase 1.5V/30A Step-Down Converter

5V

47.5k

10k

100nF

680pF

4.7µF

0.1µF

3.32k

1µF

100k

20k

10k

15k

10Ω

VCCDRVCCI

TRACK TG1
V

RNG

FCB

BOOST1

SENSE1

PGOOD

RUN/SS

EXTLPF

SENSE1

INTLPF

LTC3709

I

TH

SGND

BOOST2

V

FB

DIFFOUT

SENSE2

–

V

OS

SENSE2

+

V

OS

ON

SW1

BG1

PGND1

TG2

SW2

BG2

PGND2

324k

+

–

+

–

U

0.22µF

0.22µF

HAT2168H

HAT2165H

HAT2168H

HAT2165H

10µF
35V
×3

1.22µH

V

IN

1.22µH

+

V

4.5V TO 28V

V

1.5V
30A

330µF

2.5V
×4

3709 TA01a

IN

OUT

Efficiency and Power Loss

100

VIN = 12V

95

90

85

80

75

70

EFFICIENCY (%)

65

60

55

50

0.01 1 10 100

EFFICIENCY

POWER LOSS

0.1
LOAD CURRENT (A)

3709 TA01b

10

9

8

POWER LOSS (W)

7

6

5

4

3

2

1

0

3709fa

1

LTC3709

WW

W

U

ABSOLUTE AXI U RATI GS

Input Supply Voltage (VCC, DRVCC) ............ 7V to – 0.3V

Boosted Topside Driver Supply Voltage

(BOOST1, BOOST2) .................................. 37V to –0.3V

Switch Voltage (SW1, 2) ............................. 31V to – 1V

+

SENSE1
SENSE1
I

ON

, SENSE2+ Voltages....................... 31V to –1V

–

, SENSE2– Voltages.................... 10V to – 0.3V

Voltage ............................................... 31V to –0.3V

(BOOST – SW) Voltages ..............................7V to – 0.3V

RUN/SS, PGOOD Voltages .......................... 7V to – 0.3V

TRACK Voltage ............................................7V to –0.3V

Voltage ................................. VCC + 0.3V to –0.3V

V

RNG

UU

W

PACKAGE/ORDER I FOR ATIO

I

V

TRACK

SGND

SGND

V

OS

DIFFOUT

TOP VIEW

RNG

V

FCB

IONPGOOD

BOOST1

32 31 30 29 28 27 26 25

1RUN/SS

2

TH

3

FB

4

5

6

–

7

8

9 10 11 12

+

OS

V

32-LEAD (5mm × 5mm) PLASTIC QFN

EXPOSED PAD IS SGND (PIN 33)

MUST BE SOLDERED TO PCB
T

JMAX

33

13 14 15 16

NC

INTLPF

EXTLPF

= 125°C, θJA = 34°C/ W

BOOST2

UH PACKAGE

TG1

TG2

SW1

SW2

+

SENSE1

24

23

22

21

20

19

18

17

+

SENSE2

SENSE1

PGND1

BG1

DRV

CC

BG2

PGND2

SENSE2

V

CC

–

–

(Note 1)

ITH Voltage ............................................... 2.7V to –0.3V

V

Voltage .............................................. 2.7V to – 0.3V

FB

INTLPF, EXTLPF Voltages ........................ 2.7V to –0.3V

+

–

, V

V

OS

Voltages ................................... 7V to – 0.3V

OS

FCB Voltage ................................................ 7V to – 0.3V

Operating Temperature Range (Note 4) .. –40°C to 85°C

Junction Temperature (Note 2)............................ 125°C

Storage Temperature Range

UH Package ..................................... – 65°C to 125°C

G Package ....................................... – 65°C to 150°C

TOP VIEW

NC

PGOOD

I

ON

FCB

V

RNG

RUN/SS

I

TH

V

FB

TRACK

SGND

SGND

–

V

OS

DIFFOUT

+

V

OS

EXTLPF

INTLPF

NC

NC

36-LEAD PLASTIC SSOP

T

JMAX

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

G PACKAGE

= 125°C, θJA = 95°C/ W

36

25

34

33

32

31

30

29

28

27

26

25

24

23

22

21

20

19

BOOST1

TG1

SW1

SENSE1

SENSE1

PGND1

BG1

DRV

CC

BG2

PGND2

SENSE2

V

CC

SENSE2

SW2

TG2

BOOST2

NC

NC

+

–

–

+

ORDER PART NUMBER

LTC3709EUH

UH PART MARKING

3709

Order Options Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF

Lead Free Part Marking: http://www.linear.com/leadfree/

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

2

ORDER PART NUMBER

LTC3709EG

3709fa

LTC3709

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are at T

The ● denotes specifications which apply over the full operating

= 25°C. VCC = DRVCC = 5V, unless otherwise noted.

A

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

Main Control Loop

I

Q

Input DC Supply Current
Normal 2.4 3 mA

I

FB

V

FB

∆V

FB(LINEREG)

∆V

FB(LOADREG)

g

m(EA)

t

ON

t

ON(MIN)

t

OFF(MIN)

V

SENSE(MAX)

V

SENSE(MIN)

∆V

FB(OV)

∆V

FB(UV)

V

RUN/SS(ON)

V

RUN/SS(LE)

V

RUN/SS(LT)

I

RUN/SS(C)

I

RUN/SS(D)

Shutdown 25 65 µA
FB Pin Input Current ITH = 1.2V (Note 3) – 35 – 60 nA

Feedback Voltage ITH = 1.2V (Note 3)

●

0.594 0.600 0.606 V

Feedback Voltage Line Regulation VCC = 4.5V to 6.5V (Note 3) 0.02 %/V

Feedback Voltage Load Regulation ITH = 0.5V to 2V (Note 3) –0.12 – 0.2 %

Error Amplifier Transconductance ITH = 1.2V (Note 3) 1.3 1.45 1.6 mS

On-Time ION = 180µA, V

ION = 90µA, V

= 0V 90 116 140 ns

FCB

= 0V 180 233 280 ns

FCB

Minimum On-Time ION = 540µA 45 100 ns

Minimum Off-Time ION = 90µA 250 350 ns

Maximum Current Sense Threshold V

Minimum Current Sense Threshold V

= 1V 124 144 166 mV

RNG

V

= 0V 86 101 119 mV

RNG

V

= V

RNG

CC

= 1V – 60 mV

RNG

V

= 0V – 40 mV

RNG

V

= V

RNG

CC

177 202 234 mV

–80 mV

Overvoltage Fault Threshold 8.5 10 12.5 %

Undervoltage Fault Threshold –8.5 –10 –12.5 %

RUN Pin Start Threshold

●

0.8 1.4 2 V

RUN Pin Latchoff Enable Threshold RUN/SS Pin Rising 3 V

RUN Pin Latchoff Threshold RUN/SS Pin Falling 2.3 V

Soft-Start Charge Current –0.5 –1.2 –3 µA

Soft-Start Discharge Current 0.8 2 4 µA

UVLO Undervoltage Lockout VCC Falling 3.9 4.2 V

UVLO

TG R

TG R

BG R

BG R

(HYS)

UP

DOWN

UP

DOWN

Undervoltage Lockout Hysteresis Measured at VCC Pin 0.2 0.35 V
TG Driver Pull-Up On-Resistance TG High (Note 5) 2 Ω
TG Driver Pull-Down On-Resistance TG Low (Note 5) 1.5 Ω
BG Driver Pull-Up On-Resistance BG High (Note 5) 3 Ω
BG Driver Pull-Down On-Resistance BG Low (Note 5) 1.5 Ω

Tracking

I

TRACK

V

FB(TRACK)

TRACK Pin Input Current ITH = 1.2V, V
Feedback Voltage at Tracking V

= 0.1V, ITH = 1.2V (Note 3) 90 100 110 mV

TRACK

= 0.3V, ITH = 1.2V (Note 3) 290 300 310 mV

V

TRACK

V

= 0.5V, ITH = 1.2V (Note 3) 490 500 510 mV

TRACK

= 0.2V (Note 3) –100 –150 nA

TRACK

PGOOD Output

∆V
∆V

FBH

FBL

PGOOD Upper Threshold VFB Rising 8.5 10 12.5 %

PGOOD Lower Threshold VFB Falling –8.5 –10 –12.5 %

PG Delay PGOOD Delay VFB Rising 100 µs
∆V

FB(HYS)

I

PGOOD

V

PGL

PGOOD Hysteresis VFB Returning 3.5 %
PGOOD Leakage Current V

PGOOD Low Voltage I

= 7V ±1 µA

PGOOD

= 5mA 0.2 0.4 V

PGOOD

3709fa

3

LTC3709

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are at T

The ● denotes specifications which apply over the full operating

= 25°C. VCC = DRVCC = 5V, unless otherwise noted.

A

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Phase-Lock Loop

I

INTPLL_SOURCE

I

INTPLL_SINK

I

EXTPLL_SOURCE

I

EXTPLL_SINK

V

FCB(DC)

V

FCB(AC)

t

ON(PLL)1

t

ON(PLL)2

Internal PLL Sourcing Current 20 µA

Internal PLL Sinking Current –20 µA

External PLL Sourcing Current 20 µA

External PLL Sinking Current –20 µA
Forced Continuous Threshold Measured with a DC Voltage at FCB Pin 1.9 2.1 2.3 V
Clock Input Threshold Measured with a AC Pulse at FCB Pin 1 1.5 2 V
t

Modulation Range by External PLL

ON1

Up Modulation I
Down Modulation I

t

Modulation Range by Internal PLL

ON2

Up Modulation I
Down Modulation I

= 180µA, V

ON1

= 180µA, V

ON1

= 180µA, V

ON2

= 180µA, V

ON2

= 1.8V 186 233 ns

EXTPLL

= 0.6V 58 80 ns

EXTPLL

= 1.8V 186 233 ns

INTPLL

= 0.6V 58 80 ns

INTPLL

Differential Amplifier
A

V

V

OS

Differential Gain 0.995 1.000 1.005 V/V
Input Offset Voltage IN+ = IN

–

= 1.2V, I

= 1mA, 0.5 7 mV

OUT

Input Referred; Gain = 1
CM Common Mode Input Voltage Range I
CMRR Common Mode Rejection Ratio 0V < IN

= 1mA 0 5 V

OUT

+

–

= IN

< 5V, I

= 1mA, 45 70 dB

OUT

Input Referred
I

CL

GBP Gain Bandwidth Product I

Output Current 10 40 mA

= 1mA 2 MHz

OUT

SR Slew Rate RL = 2k 5 V/µs
V

O(MAX)

R

IN

Maximum High Output Voltage I

= 1mA V

OUT

– 1.2 V

CC

– 0.8 V

CC

Input Resistance Measured at IN+ Pin 80 kΩ

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

Note 2: T
dissipation P

is calculated from the ambient temperature TA and power

J

as follows:

D

LTC3709EUH: T

= TA + (PD • 34°C/W)

J

LTC3709EG: TJ = TA + (PD • 95°C/W)

Note 3: The LTC3709 is tested in a feedback loop that adjusts VFB to
achieve a specified error amplifier output voltage (I

).

TH

Note 4: The LTC3709E 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 5: R

limit is guaranteed by design and/or correlation to static

DS(ON)

test.

3709fa

4

UW

TYPICAL PERFOR A CE CHARACTERISTICS

LTC3709

V

RUN/SS

5V/DIV

V

OUT

1V/DIV

10A/DIV

10A/DIV

I

LOAD

3A-18A

V

OUT

50mV/DIV

V

SW1

20V/DIV

V

SW2

20V/DIV

Start-Up

I

L1

I

L2

1ms/DIV

3709 G01

Transient Response (CCM) Efficiency vs Load Current

50mV/DIV

20µs/DIV

3709 G04

Continuous Current Mode (CCM) Discontinuous Current Mode (DCM)

SW1

5V/DIV

SW2

5V/DIV

2µs/DIV

3709 G02

SW1

5V/DIV

SW2

1V/DIV

10µs/DIV

Transient Response (DCM)

100

I

LOAD

3A-18A

V

OUT

V

SW1

20V/DIV

V

SW2

20V/DIV

20µs/DIV

3709 G05

VIN = 12V

95

= 1.5V

V

OUT

f = 220kHz

90

85

80

75

70

EFFICIENCY (%)

65

60

55

50

10 1000 10000 100000

100

LOAD (mA)

3709 G03

3709 G06

Power Loss vs Load Current Quiescent Current at VCC = 5VEfficiency vs V

10

VIN = 12V

= 1.5V

V

OUT

f = 220kHz

1

0.1

POWER LOSS (W)

0.01

0.001
10 1000 10000 100000

100

LOAD CURRENT (mA)

3709 G07

100

V

OUT

I

LOAD

f = 220kHz

95

90

EFFICIENCY (%)

85

80

4

= 1.5V

= 10A

8

12

IN

VIN (V)

3.0

2.8

2.6

2.4

QUIESCENT CURRENT (mA)

2.2

2.0

16

20

24

3709 G08

–40 –20

0

TEMPERATURE (°C)

40

20

60

80

3709 G09

3709fa

5

LTC3709

TEMPERATURE (°C)

–40 –20

0

EA LOAD REGULATION (%)

0.1

0.4

0

40

60

3709 G12

0.3

0.2

20

80

TEMPERATURE (°C)

–40 –20

2.0

ARMED THRESHOLD (V)

2.5

4.0

0

40

60

3709 G15

3.5

3.0

20

80

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Shutdown Current at VCC = 5V Error Amplifier g

45

40

35

30

25

SHUTDOWN CURRENT (µA)

20

15

–40 –20

40

20

0

TEMPERATURE (°C)

60

80

3709 G10

1.6

1.5

(mS)

1.4

m

EA g

1.3

1.2
–40 –20

m

40

20

0

TEMPERATURE (°C)

60

80

3709 G11

EA Load Regulation

VFB Pin Input Current RUN/SS Threshold Armed Threshold

–20

–25

–30

–35

–40

PIN INPUT CURRENT (nA)

FB

V

–45

1.8

1.6

1.4

1.2

RUN/SS THRESHOLD (V)

1.0

–50

–40 –20

UVLO Threshold On-Time vs ION Current

4.5

4.3

4.1

3.9

UVLO THRESHOLD (V)

3.7

3.5
–40 –20

40

20

0

TEMPERATURE (°C)

40

20

0

TEMPERATURE (°C)

0.8

60

80

3709 G13

–40 –20

0

TEMPERATURE (°C)

40

20

60

80

3709 G14

Current Sense Threshold
vs I

Voltage

TH

10000

1000

ON-TIME (ns)

100

60

80

3709 G16

10

10

100 1000

ION CURRENT (µA)

3709 G17

300

250

200

150

100

50

0

–50

CURRENT SENSE THRESHOLD (mV)

–100

–150

0

0.6

V

RNG

V

= 1V

RNG

V

= 0V

RNG

1.2

ITH VOLTAGE (V)

= V

V

= 2V

RNG

CC

V

= 0.5V

RNG

1.8

2.4

3709 G18

3709fa

6

UW

TYPICAL PERFOR A CE CHARACTERISTICS

LTC3709

Maximum Current Sense
Threshold Voltage vs V

350

300

250

200

150

100

THRESHOLD VOLTAGE (mV)

MAXIMUM CURRENT SENSE

50

0

0.5

U

PI FU CTIO S

0.8 1.1 1.4 2.0
V

UU

(QFN/SSOP)

RNG

RNG

1.7

(V)

3709 G19

RUN/SS (Pin 1/Pin 6): Run Control and Soft-Start Input.
A capacitor to ground at this pin sets the ramp rate of the
output voltage (approximately 0.5s/µF) and the time delay
for overcurrent latch-off (see Applications Information).
Forcing this pin below 1.4V shuts down the device.

(Pin 2/Pin 7): Error Amplifier Compensation Point. The

I

TH

current comparator threshold increases with this control
voltage. The voltage ranges from 0V to 2.4V with 0.8V
corresponding to zero sense voltage (zero current).

V

(Pin 3/Pin 8): Error Amplifier Feedback Input. This pin

FB

connects to the error amplifier input. It can be used to
attach additional compensation components if desired.

TRACK (Pin 4/Pin 9): Tie the TRACK pin to a resistive
divider connected to the output of another LTC3709 for
either coincident or ratiometric output tracking (see Appli­cations Information). To disable this feature, tie the pin to

.

Do Not Float this pin

V

CC

.

Minimum Current Sense
Threshold Voltage vs V

0

–20

–40

–60

–80

–100

THRESHOLD VOLTAGE (mV)

MINIMUM CURRENT SENSE

–120

–140

0.8 1.1 1.4 2.0

0.5
V

RNG

RNG

1.7

(V)

3709 G20

SGND (Pins 5, 6, 33/Pins 10, 11): Signal Ground. All
small-signal components such as C

and compensation

SS

components should connect to this ground and eventually
connect to PGND at one point. The Exposed Pad of the QFN
package must be soldered to PCB ground.

–

(Pin 7/Pin 12): The (–) Input to the Differential

V

OS

Amplifer.

DIFFOUT (Pin 8/Pin 13): The Output of the Differential
Amplifier.

+

V

(Pin 9/Pin 14): The (+) Input to the Differential

OS

Amplifier.

EXTLPF (Pin 10/Pin 15): Filter Connection for the PLL.
This PLL is used to synchronize the LTC3709 with an
external clock.

INTLPF (Pin 11/Pin 16): Filter Connection for the PLL.
This PLL is use to phase shift the second channel to the
first channel by 180°.

3709fa

7

LTC3709

U

PI FU CTIO S

UU

(QFN/SSOP)

NC (Pin 12/Pins 1, 17, 18, 19, 20): No Connect.

V

(Pin 17/Pin 25): Main Input Supply. Decouple this pin

CC

to SGND with an RC filter (1Ω, 0.1µF).

DRV

(Pin 21/Pin 29): Driver Supply. Provides supply to

CC

the driver for the bottom gate. Also used for charging the
bootstrap capacitor.

BG1, BG2 (Pins 22, 20/Pins 30, 28): Bottom Gate Drive.
Drives the gate of the bottom N-channel MOSFET between
ground and DRV

CC

.

PGND1, PGND2 (Pins 23, 19/Pins 31, 27): Power Ground.
Connect this pin closely to the source of the bottom N­channel MOSFET, the (–) terminal of C
minal of C

SENSE1

.

IN

–

, SENSE2– (Pins 24, 18/Pins 32, 26): Current

and the (–) ter-

DRVCC

Sense Comparator Input. The (–) input to the current
comparator is used to accurately Kelvin sense the bottom
side of the sense resistor or MOSFET.

+

SENSE1

, SENSE2+ (Pins 25, 16/Pins 33, 24): Current

Sense Comparator Input. The (+) input to the current
comparator is normally connected to the SW node unless
using a sense resistor (see Applications Information).

TG1, TG2 (Pins 27, 14/Pins 35, 22): Top Gate Drive.
Drives the top N-channel MOSFET with a voltage swing
equal to DRV

superimposed on the switch node voltage

CC

SW.

BOOST1, BOOST2 (Pins 28, 13/Pins 36, 21): Boosted
Floating Driver Supply. The (+) terminal of the bootstrap
capacitor C
voltage drop below DRV

connects here. This pin swings from a diode

B

up to V

CC

+ DRVCC.

IN

PGOOD (Pin 29/Pin 2): Power Good Output. Open-drain
logic output that is pulled to ground when output voltage
is not within ±10% of the regulation point. The output
voltage must be out of regulation for at least 100µs before
the power good output is pulled to ground.

I

(Pin 30/Pin 3): On-Time Current Input. Tie a resistor

ON

from V

to this pin to set the one-shot timer current and

IN

thereby set the switching frequency.

FCB (Pin 31/Pin 4): Forced Continuous and External Clock
Input. Tie this pin to ground to force continuous synchro­nous operation or to V

to enable discontinuous mode

CC

operation at light load. Feeding an external clock signal
into this pin will synchronize the LTC3709 to the external
clock and enable forced continuous mode.

SW1, SW2 (Pins 26, 15/Pins 34, 23): Switch Node. The
(–) terminal of the bootstrap capacitor C

connects here.

B

This pin swings from a Schottky diode voltage drop below
ground up to V

IN

.

V

(Pin 32/Pin 5): Sense Voltage Range Input. The volt-

RNG

age at this pin is ten times the nominal sense voltage at maxi­mum output current and can be programmed from 0.5V to
2V. The sense voltage defaults to 70mV when this pin is tied
to ground, 140mV when tied to V

CC

.

3709fa

8