LINEAR TECHNOLOGY LTC3717 Technical data

FEATURES

■

V

= 1/2 VIN (Supply Splitter)

OUT

■

Adjustable and Symmetrical Sink/Source
Current Limit up to 20A

■

±0.65% Output Voltage Accuracy

■

Up to 97% Efficiency

■

No Sense Resistor Required

■

Ultrafast Transient Response

■

True Current Mode Control

■

2% to 90% Duty Cycle at 200kHz

■

t

ON(MIN)

■

Stable with Ceramic C

■

Dual N-Channel MOSFET Synchronous Drive

■

Power Good Output Voltage Monitor

■

Wide VCC Range: 4V to 36V

■

Adjustable Switching Frequency up to 1.5MHz

■

Output Overvoltage Protection

■

Optional Short-Circuit Shutdown Timer

■

Available in a 16-Pin Narrow SSOP Package

≤ 100ns

OUT

U

APPLICATIO S

■

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

■

Notebook Computers, Desktop Servers

■

Tracking Power Supply

LTC3717

Wide Operating Range,

No R

SENSE

TM

Step-Down Controller

for DDR/QDR Memory Termination

U

DESCRIPTIO

The LTC®3717 is a synchronous step-down switching
regulator controller for double data rate (DDR) and Quad
Data RateTM (QDRTM) memory termination. The controller
uses a 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 VIN.

Forced continuous operation reduces noise and RF inter­ference. Output voltage is internally set to half of V
which is user programmable.

Fault protection is provided by an output overvoltage
comparator and optional short-circuit shutdown timer.
Soft-start capability for supply sequencing is accom­plished using an external timing capacitor. The regulator
current limit level is symmetrical and user programmable.
Wide supply range allows operation from 4V to 36V at the
V

input.

CC

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

No R

is a trademark of Linear Technology Corporation.

SENSE

QDR RAMs and Quad Data Rate RAMs comprise a new family of products developed by Cypress
Semiconductor, Hitachi, IDT, Micron Technology, Inc. and Samsung.

REF

,

TYPICAL APPLICATIO

V

CC

5V TO 28V

C

470pF

1µF

C

C

SS

0.1µF

R

20k

V

CC

I

ON

V

REF

BOOST

LTC3717

INTV

PGND

SW

V

TG

CC

BG

+

FB

RUN/SS

I

TH

C

SGND

PGOOD

Figure 1. High Efficiency DDR Memory Termination Supply

R

ON

715k

= 2.5V

V

DD

CB 0.22µF

D

B

CMDSH-3

C

VCC

4.7µF

U

M1
Si7840DP

M2
Si7840DP

D2
B320A

L1

0.68µH

D1
B320A

3717 F01a

Efficiency vs Load Current

V

IN

2.5V TO 5.5V

C

+

IN

150µF

6.3V
×2

V

OUT

1.25V

C

±10A

OUT

+

180µF
4V
×2

100

90
80
70

VIN = 2.5V

60
50
40

EFFICIENCY (%)

30
20
10

0

0

V

= 1.25V

OUT

VIN = 5V

2 4 6 8 10 12 14

LOAD CURRENT (A)

3717 F01b

sn3717 3717fs

1

LTC3717

TOP VIEW

GN PACKAGE

16-LEAD PLASTIC SSOP

1
2
3
4
5
6
7
8

16
15
14
13
12
11
10

9

RUN/SS

PGOOD

V

RNG

I

TH

SGND

I

ON

V

FB

V

REF

BOOST
TG
SW
PGND
BG
INTV

CC

V

CC

EXTV

CC

WWWU

ABSOLUTE AXI U RATI GS

PACKAGE/ORDER I FOR ATIO

UU

W

(Note 1)

Input Supply Voltage (VCC, ION) .................36V to –0.3V

Boosted Topside Driver Supply Voltage

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

ORDER PART

NUMBER

LTC3717EGN

SW Voltage .................................................. 36V to –5V

EXTVCC, (BOOST – SW), RUN/SS,

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

V

, V

REF

ITH, VFB Voltages...................................... 2.7V to –0.3V

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

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

Operating Ambient Temperature

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

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

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

RNG

T

= 125°C, θJA = 130°C/W

JMAX

GN PART

MARKING

3717

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

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

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are TA = 25°C. VCC = 15V unless otherwise noted.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Main Control Loop

I

Q

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)

2

Input DC Supply Current
Normal 1000 2000 µA
Shutdown Supply Current V

Feedback Voltage Accuracy ITH = 1.2V (Note 3), V
Feedback Voltage Line Regulation VCC= 4V to 36V, ITH = 1.2V (Note 3) 0.002 %/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 = 30µA 186 233 280 ns

Minimum On-Time ION = 180µA 50 100 ns
Minimum Off-Time ION = 30µA 300 400 ns
Maximum Current Sense Threshold (Source) V

V

– V

PGND

SW

Minimum Current Sense Threshold (Sink) V

– V

V

PGND

SW

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 Threshold RUN/SS Pin Rising 4 4.5 V
RUN Pin Latchoff Threshold RUN/SS Pin Falling 3.5 4.2 V
Soft-Start Charge Current –0.5 –1.2 –3 µA
Soft-Start Discharge Current 0.8 1.8 3 µA

The ● denotes specifications which apply over the full operating

RUN/SS

= 60µA 95 115 135 ns

I

ON

RNG

V

RNG

V

RNG

RNG

V

RNG

V

RNG

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

= 0V 15 30 µA

= 2.4V –0.65 0.65 %

REF

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

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

– 50mV ● 108 135 162 mV

REF/2

– 50mV ● 76 95 114 mV

REF/2

REF/2
REF/2

– 50mV ● 148 185 222 mV

REF/2

+ 50mV ● – 140 –165 –190 mV
+ 50mV ● –97 – 115 –133 mV

+ 50mV ● –200 –235 – 270 mV

REF/2

sn3717 3717fs

LTC3717

ELECTRICAL CHARACTERISTICS

The ● denotes specifications which apply over the full operating

temperature range, otherwise specifications are TA = 25°C. VCC = 15V unless otherwise noted.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

CC(UVLO)

V

CC(UVLOR)

TG R

UP

TG R

DOWN

BG R

UP

BG R

DOWN

TG t

r

TG t

f

BG t

r

BG t

f

Internal VCC Regulator

V

INTVCC

∆V

LDO(LOADREG)

V

EXTVCC

∆V

EXTVCC

∆V

EXTVCC(HYS)

PGOOD Output

∆V

FBH

∆V

FBL

∆V

FB(HYS)

V

PGL

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

Note 2: T
dissipation P

LTC3717EGN: TJ = TA + (PD • 130°C/W)

Undervoltage Lockout Threshold VCC Falling ● 3.4 3.9 V
Undervoltage Lockout Threshold VCC Rising ● 3.5 4 V
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

Internal VCC Voltage 6V < VCC < 30V, V
Internal VCC Load Regulation ICC = 0mA to 20mA, V
EXTVCC Switchover Voltage ICC = 20mA, V
EXTVCC Switch Drop Voltage ICC = 20mA, V

= 3300pF 20 ns

LOAD

= 3300pF 20 ns

LOAD

= 3300pF 20 ns

LOAD

= 3300pF 20 ns

LOAD

= 4V ● 4.7 5 5.3 V

EXTVCC

= 4V –0.1 ±2%

EXTVCC

Rising ● 4.5 4.7 V

EXTVCC

= 5V 150 300 mV

EXTVCC

EXTVCC Switchover Hysteresis 200 mV

PGOOD Upper Threshold VFB Rising (0% = 1/3 V
PGOOD Lower Threshold VFB Falling (0% = 1/3 V
PGOOD Hysteresis VFB Returning (0% = 1/3 V
PGOOD Low Voltage I

= 5mA 0.15 0.4 V

PGOOD

) 8 10 12 %

REF

)–8–10–12%

REF

)12%

REF

Note 3: The LTC3717 is tested in a feedback loop that adjusts VFB to achieve

).

TH

is calculated from the ambient temperature TA and power

J

as follows:

D

a specified error amplifier output voltage (I
Note 4: The LTC3717E 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.

sn3717 3717fs

3

LTC3717

ION CURRENT (µA)

1

10

ON-TIME (ns)

100

1k

10k

10 100

3717 G13

UW

TYPICAL PERFOR A CE CHARACTERISTICS

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

Load Regulation

(%)

OUT

/V

OUT

∆V

0

–0.1

–0.2

–0.3

–0.4

VIN = 2.5V
V

OUT

3717 G06

= 1.25V

(%)

IN

/V

OUT

V

50.00

49.95

49.90

49.85

49.80

49.75

49.70

49.65

V
Voltage

1.5

Tracking Ratio vs Input

OUT/VIN

LOAD = 0A

LOAD = 1A

LOAD = 10A

FIGURE 1 CIRCUIT

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

3717 G07

Frequency vs Input Voltage

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

Start-Up Response Load-Step Transient

V

OUT

1V/DIV

2A/DIV

I

L

V

OUT

200mV/DIV

5A/DIV

I

L

LOAD = 10A

LOAD = 0A

= 1.25V

INPUT VOLTAGE (V)

3717 G08

–0.5

FIGURE 1 CIRCUIT

–0.6

0

On-Time vs V

1000

I

ION

800

600

400

ON-TIME (ns)

200

0

0

1 2 3 4 5 6 7 8 910

LOAD CURRENT (A)

3717 G09

Voltage

ON

= 30µA

1

VON VOLTAGE (V)

2

3

3717 G11

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

= 1.25V

OUT

LOAD = 0.2Ω
FIGURE 1 CIRCUIT

VIN = 2.5V 20µs/DIV 3718 G10.eps
V

OUT

LOAD = 500mA TO 10A STEP
FIGURE 1 CIRCUIT

On-Time vs Temperature On-Time vs I

300

I

= 30µA

ION

250

200

150

ON-TIME (ns)

100

50

0

–50

–25 0

TEMPERATURE (°C)

50 100 125

25 75

3717 G12

= 1.25V

ON

Current

sn3717 3717fs

4

UW

TEMPERATURE (°C)

–50

3.0

RUN/SS THRESHOLD (V)

3.5

4.0

4.5

5.0

–25 0 25 50

3717 G16

75 100 125

LATCHOFF ENABLE

LATCHOFF THRESHOLD

TYPICAL PERFOR A CE CHARACTERISTICS

LTC3717

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

3.0

2.5

UNDERVOLTAGE LOCKOUT THRESHOLD (V)

2.0
–50

–25 0 25 50

TEMPERATURE (C)

75 100 125

RUN/SS Latchoff Thresholds
vs Temperature

3

2

PULL-DOWN CURRENT

1

0

FCB PIN CURRENT (µA)

–1

–2

40

50

3717 G14

–50 –25

PULL-UP CURRENT

50

25

0

TEMPERATURE (°C)

100

125

3717 G15

75

Maximum Current Sense Threshold
vs V

Voltage

RNG

300

250

200

150

100

50

MAXIMUM CURRENT SENSE THRESHOLD (mV)

3717 G17

0

0.50

1.00 1.25 1.50

0.75
V

(V)

RNG

1.75 2.00

3717 G18

RUN/SS Latchoff Thresholds
vs Temperature

Maximum Current Sense Threshold
vs RUN/SS Voltage, V

160

140

120

100

80

60

40

20

MAXIMUM CURRENT SENSE THRESHOLD (mV)

0

2.0

2.4

2.8 3.0 3.2 3.42.2

2.6
RUN/SS (V)

RNG

= 1V

3.6

3717 G19

MAXIMUM CURRENT SENSE THRESHOLD (mV)

Maximum Current Sense Threshold
vs Temperature, V

180

160

140

120

100

80

60

40

20

0

–50 130

–30 –10

10 30 50 90

TEMPERATURE (°C)

RNG

= 1V

70

110

3717 G20

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)

70

110

3717 G21

sn3717 3717fs

5

LTC3717

U

UU

PI FU CTIO S

RUN/SS (Pin 1): Run Control and Soft-Start Input. A
capacitor to ground at this pin sets the ramp time to full
output current (approximately 3s/µF) and the time delay
for overcurrent latchoff (see Applications Information).
Forcing this pin below 0.8V shuts down the device.

PGOOD (Pin 2): Power Good Output. Open drain logic
output that is pulled to ground when the output voltage is
not within ±10% of the regulation point.

V

(Pin 3): Sense Voltage Range Input. The voltage at

RNG

this pin is ten times the nominal sense voltage at maxi­mum output current and can be set from 0.5V to 2V by a
resistive divider from INTVCC. The nominal sense voltage
defaults to 70mV when this pin is tied to ground, 140mV
when tied to INTVCC.

I

(Pin 4): Current Control Threshold and Error Amplifier

TH

Compensation Point. The 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).

SGND (Pin 5): Signal Ground. All small-signal compo­nents and compensation components should connect to
this ground, which in turn connects to PGND at one point.

ION (Pin 6): On-Time Current Input. Tie a resistor from V
to this pin to set the one-shot timer current and thereby set
the switching frequency.

VFB (Pin 7): Error Amplifier Feedback Input. This pin
connects to V
through precision internal resistors before it is applied to
the input of the error amplifier. Do not apply more than

1.5V on VFB. For higher output voltages, attach an external
resistor R2 (1/2 • R1 at V

V

(Pin 8): Positive Input of Internal Error Amplifier.

REF

This pin connects to an external reference and divides its
voltage to 1/3 V

and divides its voltage to 2/3 • V

OUT

) from V

REF

through precision internal resisters

REF

OUT

to VFB.

IN

FB

before it is applied to the positive input of the error
amplifier. Reference voltage for output voltage, power
good threshold, and short-circuit shutdown threshold. Do
not apply more than 3V on V
used, connect an external resistor (R1 ≥ 160k) from
voltage reference to V

EXTVCC (Pin 9): External VCC Input. When EXTVCC ex-
ceeds 4.7V, an internal switch connects this pin to INTV
and shuts down the internal regulator so that controller
and gate drive power is drawn from EXTVCC. Do not exceed
7V at this pin and ensure that EXTVCC < VCC.

VCC (Pin 10): Bias Input Supply. 4V to 36V operating
range. Decouple this pin to PGND with an RC filter (1Ω,

0.1µF).
INTVCC (Pin 11): Internal 5V Regulator Output. The driver

and control circuits are powered from this voltage. De­couple this pin to power ground with a minimum of 4.7µF
low ESR tantalum or ceramic capacitor.

BG (Pin 12): Bottom Gate Drive. Drives the gate of the
bottom N-channel MOSFET between ground and INTVCC.

PGND (Pin 13): Power Ground. Connect this pin closely to
the source of the bottom N-channel MOSFET, the (–)
terminal of C

SW (Pin 14): Switch Node. The (–) terminal of the boot­strap capacitor CB connects here. This pin swings from a
diode voltage drop below ground up to a diode voltage
drop above VIN.

TG (Pin 15): Top Gate Drive. Drives the top N-channel
MOSFET with a voltage swing equal to INTVCC superim­posed on the switch node voltage SW.

BOOST (Pin 16): Boosted Floating Driver Supply. The (+)
terminal of the bootstrap capacitor CB connects here. This
pin swings from a diode voltage drop below INTVCC up to
V

+ INTVCC.

IN

and the (–) terminal of CIN.

VCC

REF

.

. If higher voltages are

REF

CC

6

sn3717 3717fs