LTC3718EG Linear Technology, LTC3718EG Datasheet

IC DC/DC CONTRLR DDR/QDR 24-SSOP

LTC3718EG

Manufacturer Part Number
LTC3718EG
Description
IC DC/DC CONTRLR DDR/QDR 24-SSOP
Manufacturer
Linear Technology
Datasheet

Specifications of LTC3718EG

Applications
Controller, DDR, QDR
Voltage - Input
1.5 ~ 36 V
Number Of Outputs
1
Voltage - Output
0.75 ~ 18 V
Operating Temperature
-40°C ~ 85°C
Mounting Type
Surface Mount
Package / Case
24-SSOP
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant

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FEATURES
TYPICAL APPLICATIO
APPLICATIO S
Figure 1. High Efficiency Bus Termination Supply without Auxiliary 5V Supply
C1 820pF X7R
Very Low V
Ultrafast Transient Response
True Current Mode Control
5V Drive for N-Channel MOSFETs Eliminates
Auxillary 5V Supply
No Sense Resistor Required
Uses Standard 5V Logic-Level N-Channel MOSFETs
V
V
Symmetrical Source and Sink Output Current Limit
Adjustable Switching Frequency
t
Power Good Output Voltage Monitor
Programmable Soft-Start
Output Overvoltage Protection
Optional Short-Circuit Shutdown Timer
Small 24-Lead SSOP Package
Bus Termination: DDR/QDR Memory, SSTL, HSTL, ...
Servers, RAID Systems
Distributed Power Systems
Synchronous Buck with General Purpose Boost
C
ON(MIN)
OUT
OUT(MIN)
OUT
R
: SANYO POSCAP 4TPB470M
F1
12.1k
Tracks 1/2 V
0.1 F
C
R
SS
C
<100ns
V
237k
4.75k
R
OUT
: 0.4V
ON
IN(MIN)
SHDN
V
I
V
PGOOD
RUN/SS
I
SGND1
SGND2
V
ON
TH
REF
FB1
FB2
U
LTC3718
R
: 1.5V
IN
F2
37.4k
L1: SUMIDA CEP125-0R8MC
or External V
SENSE
SENSE
BOOST
PGND1
INTV
PGND2
SW1
SW2
V
V
IN1
IN2
TG
BG
CC
+
U
REF
D
CMDSH-3
C
0.33 F
C
10 F
B
B
VCC1
C
4.7 F
IN2
L2: PANASONIC ELJPC4R7MF
L2
4.7 H
D3
MBR0520
M1
Si7440DP
M2
Si7440DP
L1 0.8 H
D1
B340A
D2
B340A
22 F
C
IN1
DDR/QDR Memory Termination
2
+
DESCRIPTIO
The LTC
nous switching regulator controller for DDR and QDR
memory termination. It operates from an input as low as
1.5V and provides a regulated output voltage equal to
(0.5)V
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 com-
pensated for variations in V
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 inter-
ference. Fault protection is provided by internal foldback
current limiting, an output overvoltage comparator and an
optional short-circuit timer. Soft-start capability for sup-
ply sequencing can be accomplished using an external
timing capacitor. OPTI-LOOP
transient response to be optimized over a wide range of
loads and output capacitors.
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.
C
470 F
OUT
2
, LTC and LT are registered trademarks of Linear Technology Corporation.
3718 TA01
V
2.5V
V
1.25V
V
IN
OUT
10A
IN
IN
. The controller uses a valley current control
®
3718 is a high current, high efficiency synchro-
DC/DC Controller for
U
100
90
80
70
60
50
40
30
20
10
Low Input Voltage
0
0.01
Efficiency vs Load Current
V
V
IN
OUT
= 2.5V
IN
= 1.25V
0.1
and V
®
LOAD CURRENT (A)
compensation allows the
OUT
1
FIGURE 1 CIRCUIT
. The LTC3718 uses
10
LTC3718
3718 G05/TA01a
SENSE
100
is a
3718fa
1
TM

Related parts for LTC3718EG

LTC3718EG Summary of contents

Page 1

... LTC and LT are registered trademarks of Linear Technology Corporation. OPTI-LOOP is a registered trademark of Linear Technology Corporation 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 ...

Page 2

... RNG CC FB1 REF 50mV RNG FB1 REF 50mV RNG FB1 REF V = INTV , 50mV RNG CC FB1 REF RUN/SS Pin Rising U W ORDER PART TOP VIEW NUMBER 1 BOOST 24 LTC3718EG SW1 + 4 21 SENSE – SENSE 6 19 PGND1 INTV IN1 IN2 11 14 PGND2 ...

Page 3

ELECTRICAL CHARACTERISTICS temperature range, otherwise specifications are T SYMBOL PARAMETER V RUN Pin Latchoff Threshold RUN/SS(LT) I Soft-Start Charge Current RUN/SS(C) I Soft-Start Discharge Current RUN/SS( Undervoltage Lockout IN(UVLO) IN1 Driver Pull-Up On Resistance UP ...

Page 4

... LTC3718 ELECTRICAL CHARACTERISTICS Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note calculated from the ambient temperature T J dissipation P as follows: D LTC3718EG • 130 C/ TYPICAL PERFOR A CE CHARACTERISTICS Boost Converter Oscillator Frequency vs Temperature 2.00 ...

Page 5

W U TYPICAL PERFOR A CE CHARACTERISTICS Frequency vs Input Voltage 450 400 LOAD = 10A 350 300 250 LOAD = 0A 200 150 100 V = 1.25V OUT 50 FIGURE 1 CIRCUIT 0 1.5 1.7 1.9 2.1 INPUT VOLTAGE ...

Page 6

LTC3718 W U TYPICAL PERFOR A CE CHARACTERISTICS INTV Load Regulation CC 0 –0.1 –0.2 –0.3 –0.4 –0 INTV LOAD CURRENT (mA) CC 3718 G14 Undervoltage Lockout Threshold vs Temperature 4.0 3.5 3.0 2.5 2.0 ...

Page 7

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/ F) and the time delay for overcurrent latchoff ...

Page 8

LTC3718 CTIO AL DIAGRA 0.7V 2.4V V VON t = (10pF ION 20k + I CMP – 1.4V V RNG 4 0.7V 5 240k ...

Page 9

U OPERATIO Main Control Loop The LTC3718 is a current mode controller for DC/DC step-down converters designed to operate from low input voltages. It incorporates a boost converter with a buck regulator. Buck Regulator Operation In normal operation, the top ...

Page 10

LTC3718 U U APPLICATIO S I FOR ATIO A typical LTC3718 application circuit is shown in Figure 1. External component selection is primarily de- termined by the maximum load current and begins with the selection of the sense resistance and ...

Page 11

U U APPLICATIO S I FOR ATIO 2.0 1.5 1.0 0.5 0 – JUNCTION TEMPERATURE ( C) Figure Temperature DS(ON) V OUT D TOP – OUT D BOT V ...

Page 12

LTC3718 U U APPLICATIO S I FOR ATIO R VON1 30k V OUT R VON2 100k (3a) Figure 3. Adjusting Frequency Shift with Load Current Changes filter out the I variations at the switching frequency. The ...

Page 13

U U APPLICATIO S I FOR ATIO transients. The output ripple V bounded by ESR OUT OUT Since I increases with input voltage, the output ripple is L highest at maximum input voltage. Typically, ...

Page 14

LTC3718 U U APPLICATIO S I FOR ATIO due to a dropping input voltage for example, then the output will drop out of regulation. The minimum input voltage to avoid dropout is OFF MIN ( ) V ...

Page 15

U U APPLICATIO S I FOR ATIO persists until the RUN/SS pin drops to 3.5V, then the con- troller turns off both power MOSFETs, shutting down the converter permanently. The RUN/SS pin must be actively pulled down to ground in ...

Page 16

LTC3718 U U APPLICATIO S I FOR ATIO losses. These arise from the resistances of the MOSFETs, inductor and PC board traces and cause the efficiency to drop at high output currents. In continuous mode ...

Page 17

U U APPLICATIO S I FOR ATIO and double check the assumed T in the MOSFET – 013 ...

Page 18

LTC3718 U U APPLICATIO S I FOR ATIO PC Board Layout Checklist When laying out a PC board follow one of the two suggested approaches. The simple PC board layout requires a dedicated ground plane layer. Also, for higher currents, ...

Page 19

... DIMENSIONS ARE IN 3. DRAWING NOT TO SCALE Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. One Half V ...

Page 20

... High Power DDR Memory Termination Regulator LTC3778 No R Synchronous Step-Down Controller SENSE LTC3831 High Power DDR Memory Termination Regulator No R and ThinSOT are trademarks of Linear Technology Corporation. SENSE Linear Technology Corporation 20 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 C SS ...

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