LINEAR TECHNOLOGY LTC3718 Technical data

FEATURES

LTC3718

Low Input Voltage

DC/DC Controller for

DDR/QDR Memory Termination

U

DESCRIPTIO

■

Very Low V

■

Ultrafast Transient Response

■

True Current Mode Control

■

5V Drive for N-Channel MOSFETs Eliminates

IN(MIN)

: 1.5V

Auxillary 5V Supply

■

No Sense Resistor Required

■

Uses Standard 5V Logic-Level N-Channel MOSFETs

■

V

OUT(MIN)

■

V

OUT

■

Symmetrical Source and Sink Output Current Limit

■

Adjustable Switching Frequency

■

t

ON(MIN)

■

Power Good Output Voltage Monitor

■

Programmable Soft-Start

■

Output Overvoltage Protection

■

Optional Short-Circuit Shutdown Timer

■

Small 24-Lead SSOP Package

: 0.4V

Tracks 1/2 VIN or External V

<100ns

REF

U

APPLICATIO S

■

Bus Termination: DDR/QDR Memory, SSTL, HSTL, ...

■

Servers, RAID Systems

■

Distributed Power Systems

■

Synchronous Buck with General Purpose Boost

The LTC®3718 is a high current, high efficiency synchronous switching regulator controller for DDR and QDR

TM

memory termination. It operates from an input as low as

1.5V and provides a regulated output voltage equal to (0.5)VIN. The controller uses a valley current control architecture to enable high frequency operation with very low on-times without requiring a sense resistor. Operating frequency is selected by an external resistor and is compensated for variations in VIN and V

. The LTC3718 uses

OUT

a pair of standard 5V logic level N-channel external MOSFETs, eliminating the need for expensive P-channel or low threshold devices.

Forced continuous operation reduces noise and RF interference. Fault protection is provided by internal foldback current limiting, an output overvoltage comparator and an optional short-circuit timer. Soft-start capability for supply sequencing can be accomplished using an external timing capacitor. OPTI-LOOP® compensation allows the transient response to be optimized over a wide range of loads and output capacitors.

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

OPTI-LOOP is a registered trademark of Linear Technology Corporation. No R trademark of Linear Technology Corporation. QDR RAMs and Quad Data Rate RAMs comprise a new family of products developed by Cypress Semiconductor, IDT and Micron Technology, Inc.

SENSE

is a

U

TYPICAL APPLICATIO

V

IN

C

OUT

470µF ×2

2.5V

V

OUT

1.25V ±10A

V

IN

3718 TA01

C

L1 0.8µH

IN1

22µF

×2

D1 B340A

+

D

B

SHDN BOOST

LTC3718

RF2 37.4k

SENSE

INTV

PGND2

SW1

V V

SW2

TG

+

–

BG

CC

IN1 IN2

V

REF

R

ON

237k

I

ON

V

FB1

OUT

C

4.75k

PGOOD PGND1

RUN/SS

I

TH

SGND1

SGND2

V

FB2

C

SS

0.1µF

C1 820pF X7R

C

R

RF1 12.1k

: SANYO POSCAP 4TPB470M L1: SUMIDA CEP125-0R8MC L2: PANASONIC ELJPC4R7MF

OUT

CMDSH-3

C

B

0.33µF

C

4.7µF

C

VCC1

10µF

IN2

M1 Si7440DP

M2 Si7440DPD2B340A

L2

4.7µH

D3 MBR0520

Figure 1. High Efficiency Bus Termination Supply without Auxiliary 5V Supply

Efficiency vs Load Current

100

VIN = 2.5V

90

= 1.25V

V

OUT

80 70 60 50 40

EFFICIENCY (%)

30 20 10

0

0.01 1 10 100

0.1

FIGURE 1 CIRCUIT

LOAD CURRENT (A)

3718 G05/TA01a

3718fa

1

LTC3718

WWWU

ABSOLUTE AXI U RATI GS

(Note 1)

Input Supply Voltage (V Boosted Topside Driver Supply Voltage

(BOOST) ............................................... 42V to –0.3V

V

, ION, SW1 Voltage ............................. 36V to –0.3V

IN1

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

VON, V ITH, V

, V

REF

Voltages .................................... 2.7V to –0.3V

FB1

Voltages .......(INTVCC + 0.3V) to –0.3V

RNG

SW2 Voltage ............................................. 36V to – 0.4V

V

Voltage ................................................. V

FB2

SHDN Voltage ......................................................... 10V

TG, BG, INTVCC Peak Currents.................................. 2A

TG, BG, INTVCC RMS Currents ............................ 50mA

Operating Ambient Temperature

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

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

Storage Temperature Range ................. –65°C to 150°C

Lead Temperature (Soldering, 10 sec).................. 300°C

) .......................10V to –0.3V

IN2

+ 0.3V

UU

W

PACKAGE/ORDER I FOR ATIO

TOP VIEW

RUN/SS

1 2

V

ON

3

PGOOD

4

V

RNG

5

I

TH

6

SGND1

7

I

ON

8

V

FB1

9

V

REF

10

SHDN

11

SGND2

12

V

FB2

24-LEAD PLASTIC SSOP

T

JMAX

G PACKAGE

= 125°C, θJA = 130°C/W

BOOST

24

TG

23

SW1

22 21 20 19 18 17 16 15 14 13

SENSE SENSE PGND1 BG INTV V

IN1

V

IN2

PGND2 SW2

+

–

CC

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

ORDER PART

NUMBER

LTC3718EG

ELECTRICAL CHARACTERISTICS

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

The ● denotes specifications which apply over the full operating

= 15V, V

IN1

= 1.5V unless otherwise noted.

IN2

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Buck Regulator

I

Q(VIN1)

Input DC Supply Current (V

IN1

)

Normal 1000 2000 µA

= 0V 15 30 µA

RUN/SS

= 4V to 36V, ITH = 1.2V (Note 3) 0.002 %/V

IN1

= 30µA, VON = 1.5V 400 500 600 ns

I

ON

V

RNG RNG RNG

= 1V, V = 0V, V = INTVCC, V

FB1 FB1

= V

/2 – 50mV ● 108 135 162 mV

REF

= V

/2 – 50mV ● 76 95 114 mV

REF

= V

FB1

= V = V

FB1

/2 – 50mV ● 148 185 222 mV

REF

/2 + 50mV –140 –165 –190 mV

REF

/2 + 50mV –97 –115 –133 mV

REF

= V

/2 + 50mV –200 –235 – 270 mV

REF

V

FB1

∆V

FB1(LINE)

∆V

FB1(LOAD)

g

m(EA)

t

ON

t

ON(MIN)

t

OFF(MIN)

V

SENSE(MAX)

V

SENSE(MIN)

∆V

FB1(OV)

∆V

FB1(UV)

V

RUN/SS(ON)

V

RUN/SS(LE)

Shutdown Supply Current V Feedback Voltage Accuracy ITH = 1.2V (Note 3) ● –0.65 0.1 0.65 % Feedback Voltage Line Regulation V Feedback Voltage Load Regulation ITH = 0.5V to 1.9V (Note 3) ● –0.05 –0.3 % Error Amplifier Transconductance ITH = 1.2V (Note 3) 0.93 1.13 1.33 mS On-Time ION = 60µA, VON = 1.5V 200 250 300 ns

Minimum On-Time ION = 180µA 50 100 ns Minimum Off-Time 300 400 ns Maximum Current Sense Threshold V

– V

V

PGND

(Source) V

SW1

Minimum Current Sense Threshold V

– V

V

PGND

(Sink) V

SW1

Output Overvoltage Fault Threshold 8 10 12 % Output Undervoltage Fault Threshold –25 % RUN Pin Start Threshold ● 0.8 1.5 2 V RUN Pin Latchoff Enable RUN/SS Pin Rising 4 4.5 V

2

3718fa

LTC3718

ELECTRICAL CHARACTERISTICS

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

The ● denotes specifications which apply over the full operating

= 15V, V

IN1

= 1.5V unless otherwise noted.

IN2

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

RUN/SS(LT)

I

RUN/SS(C)

I

RUN/SS(D)

V

IN(UVLO)

TG R

UP

TG R

DOWN

BG R

UP

BG R

DOWN

TG t

r

TG t

f

BG t

r

BG t

f

RUN Pin Latchoff Threshold RUN/SS Pin Falling 3.5 4.2 V Soft-Start Charge Current V Soft-Start Discharge Current V V

Undervoltage Lockout VIN Falling ● 3.4 3.9 V

IN1

= 0V –0.5 –1.2 –3 µA

RUN/SS

= 4.5V, V

RUN/SS

Rising ● 3.5 4.0 V

V

IN

= 0V 0.8 1.8 3 µA

FB

TG Driver Pull-Up On Resistance TG High 2 3 Ω TG Driver Pull-Down On Resistance TG Low 2 3 Ω BG Driver Pull-Up On Resistance BG High 3 4 Ω BG Driver Pull-Down On Resistance BG Low 1 2 Ω TG Rise Time C TG Fall Time C BG Rise Time C BG Fall Time C

= 3300pF 20 ns

LOAD

= 3300pF 20 ns

LOAD

= 3300pF 20 ns

LOAD

= 3300pF 20 ns

LOAD

Internal VCC Regulator

V

INTVCC

∆V

LDO(LOAD)

Internal VCC Voltage 6V < V

<30V ● 4.7 5 5.3 V

IN1

Internal VCC Load Regulation ICC = 0mA to 20mA –0.1 ±2%

PGOOD Output

∆V

FB1H

∆V

FB1L

∆V

FB1(HYS)

V

PGL

PGOOD Upper Threshold V PGOOD Lower Threshold V PGOOD Hysterisis V PGOOD Low Voltage I

= Rising 8 10 12 %

FB1

= Falling –8 –10 – 12 %

FB1

= Returning 1 2 %

FB1

= 5mA 0.15 0.4 V

PGOOD

Boost Regulator

V

IN2(MIN)

V

IN2(MAX)

I

Q(VIN2)

Minimum Operating Voltage 0.9 1.5 V Maximum Operating Voltage 10 V Input DC Supply Current (V

IN2

)

Normal 3 4.5 mA

=0V 0.01 1 µA

SHDN

● 1.20 1.23 1.26 V

< 10V 0.02 0.2 %/V

IN2

● 0.9 1.4 1.9 MHz

ISW = 300mA 300 350 mV

= 3V 25 50 µA

SHDN

= 0V 0.01 0.1 µA

V

SHDN

V

FB2

I

VFB2

∆V

FB2(LINE)

f

BOOST

DC

BOOST(MAX)

I

LIM(BOOST)

V

CESAT(BOOST)

I

SWLKG(BOOST)

V

SHDN(HIGH)

V

SHDN(LOW)

I

SHDN

Shutdown Supply Current V V

Feedback Voltage 0°C < T < 70°C 1.205 1.23 1.255 V

FB2

V

Pin Bias Current ● 27 80 nA

FB2

Boost Reference Line Regulation 1.5V < V BOOST Switching Frequency 0°C < T < 70°C 1.0 1.4 1.8 MHz

BOOST Maximum Duty Cycle 82 86 % BOOST Switch Current Limit (Note 5) 500 800 mA BOOST Switch V

CESAT

BOOST Switch Leakage Current VSW = 5V 0.01 1 µA SHDN Input Voltage High 1 V SHDN Input Voltage Low 0.3 V SHDN Pin Bias Current V

3718fa

3

LTC3718

ELECTRICAL CHARACTERISTICS

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

LTC3718EG: TJ = TA + (PD • 130°C/W)

Note 3: The LTC3718 is tested in a feedback loop that adjusts V achieve a specified error amplifier output voltage (I

Note 4: The LTC3718 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: Current limit guaranteed by design and/or correlation to static test.

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Boost Converter Oscillator Frequency vs Temperature

2.00

1.75

1.50

1.25

1.00

0.75

0.50

SWITCHING FREQUENCY (MHz)

0.25

VIN = 5V

VIN = 1.5V

0

–50 –25 0 25 50 75 100

TEMPERATURE (°C)

3718 G01

SHDN Pin Current vs V

50

TA = 25°C

40

30

20

10

SHDN PIN BIAS CURRENT (µA)

0

012345

SHDN PIN VOLTAGE (V)

SHDN

3718 G02

).

TH

Boost Converter Current Limit vs Duty Cycle

1000

900

800

700

600

500

CURRENT LIMIT (mA)

400

300

200

10 20 30 40 50 60 70 80

70°C

25°C

–40°C

DUTY CYCLE (%)

FB1

to

3718 G03

V

, Feedback Pin Voltage

FB2

1.25

1.24

1.23

1.22

FEEDBACK PIN VOLTAGE (V)

1.21

FIGURE 1 CIRCUIT

1.20 –25 0 25 50 75 100

–50

TEMPERATURE (°C)

3718 G04

Efficiency vs Load Current

100

VIN = 2.5V

90 80 70 60 50 40

EFFICIENCY (%)

30 20 10

= 1.25V

V

OUT

0

0.01 1 10 100

0.1 LOAD CURRENT (A)

FIGURE 1 CIRCUIT

3718 G05/TA01a

50.00

49.95

49.90

49.85

(%)

IN

/V

49.80

OUT

V

49.75

49.70

49.65

V

Tracking Ratio vs Input

OUT/VIN

Voltage

LOAD = 0A

LOAD = 1A

LOAD = 10A

FIGURE 1 CIRCUIT

1.5

1.7 1.9 2.1 2.3 2.5 2.7 2.9 INPUT VOLTAGE (V)

3718 G06

3718fa

4

UW

LOAD CURRENT (A)

0

1 2 3 4 5 6 7 8 910

∆V

OUT

/V

OUT

(%)

3718 G08

0

–0.1

–0.2

–0.3

–0.4

–0.5

–0.6

VIN = 2.5V V

OUT

= 1.25V

FIGURE 1 CIRCUIT

TYPICAL PERFOR A CE CHARACTERISTICS

Frequency vs Input Voltage Load Regulation

450

400

350

300

250

200

150

FREQUENCY (kHz)

100

V

OUT

50

FIGURE 1 CIRCUIT

0

1.5 1.7 1.9 2.1 2.3 2.5 2.7 2.9

LOAD = 10A

LOAD = 0A

= 1.25V

INPUT VOLTAGE (V)

3718 G07

LTC3718

On-Time vs V

1000

I

ION

800

600

400

ON-TIME (ns)

200

0

200mV/DIV

= 30µA

Load-Step Transient

V

OUT

I

L

5A/DIV

VIN = 2.5V 20µs/DIV 3718 G10.eps V

OUT

LOAD = 500mA TO 10A STEP FIGURE 1 CIRCUIT

Voltage

ON

1

VON VOLTAGE (V)

= 1.25V

2

3718 G11

3

Start-Up Response

V

OUT

1V/DIV

I

L

2A/DIV

VIN = 2.5V 4ms/DIV 3718 G09.eps V

= 1.25V

OUT

LOAD = 0.2Ω FIGURE 1 CIRCUIT

On-Time vs Temperature On-Time vs I

300

I

ION

250

200

150

ON-TIME (ns)

100

50

0

–50

= 30µA

–25 0

50 100 125

25 75

TEMPERATURE (°C)

3718 G12

10k

1k

ON-TIME (ns)

100

10

1

Current

ON

10 100

ION CURRENT (µA)

V

= 0V

VON

3718 G13

3718fa

5

LTC3718

TEMPERATURE (°C)

–50

3.0

RUN/SS THRESHOLD (V)

3.5

4.0

4.5

5.0

–25 0 25 50

3718 G16

75 100 125

LATCHOFF ENABLE

LATCHOFF THRESHOLD

RUN/SS (V)

2.0

MAXIMUM CURRENT SENSE THRESHOLD (mV)

3.6

2718 G19

2.8 3.0 3.2 3.42.2

2.4

2.6

160

140

120

100

80

60

40

20

0

UW

TYPICAL PERFOR A CE CHARACTERISTICS

INTVCC Load Regulation

0

–0.1

–0.2

(%)

CC

–0.3

∆INTV

–0.4

–0.5

10

0

INTVCC LOAD CURRENT (mA)

30

20

Undervoltage Lockout Threshold vs Temperature

4.0

3.5

RUN/SS Latchoff Thresholds vs Temperature

3

2

PULL-DOWN CURRENT

1

0

FCB PIN CURRENT (µA)

–1

–2

40

50

3718 G14

–50 –25

PULL-UP CURRENT

50

25

0

TEMPERATURE (°C)

100

125

3718 G15

75

Maximum Current Sense Threshold vs V

Voltage

RNG

300

250

200

RUN/SS Latchoff Thresholds vs Temperature

Maximum Current Sense Threshold vs RUN/SS Voltage, V

RNG

= 1V

3.0

2.5

UNDERVOLTAGE LOCKOUT THRESHOLD (V)

2.0 –50

–25 0 25 50

TEMPERATURE (C)

180

160

140

120

6

100

80

60

40

20

MAXIMUM CURRENT SENSE THRESHOLD (mV)

150

100

50

MAXIMUM CURRENT SENSE THRESHOLD (mV)

75 100 125

3718 G17

0

0.50

Maximum Current Sense Threshold vs Temperature, V

0

–50 130

–30 –10

10 30 50 90

TEMPERATURE (°C)

RNG

= 1V

70

110

3718 G20

1.00 1.25 1.50

0.75 V

(V)

RNG

1.75 2.00

3718 G18

Error Amplifier gm vs Temperature

1.50

1.40

1.30

1.20

1.10

gm (ms)

1.00

0.90

0.80

0.70 –50 130

–30 –10

10 30 50 90

TEMPERATURE (°C)

110

70

3718 G21

3718fa

LINEAR TECHNOLOGY LTC3718 Technical data

Specifications and Main Features

Frequently Asked Questions

User Manual