FEATURES
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LTC3718
Low Input Voltage
DC/DC Controller for
DDR/QDR Memory Termination
DESCRIPTIO
The LTC
®
3718 is a high current, high efficiency synchro-
nous 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)V
IN
. 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 com-
pensated for variations in V
IN
and V
OUT
. The LTC3718 uses
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
®
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
SENSE
is a
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.
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Very Low V
IN(MIN)
: 1.5V
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
OUT(MIN)
: 0.4V
V
OUT
Tracks 1/2 V
IN
or External V
REF
Symmetrical Source and Sink Output Current Limit
Adjustable Switching Frequency
t
ON(MIN)
<100ns
Power Good Output Voltage Monitor
Programmable Soft-Start
Output Overvoltage Protection
Optional Short-Circuit Shutdown Timer
Small 24-Lead SSOP Package
APPLICATIO S
s
s
s
s
Bus Termination: DDR/QDR Memory, SSTL, HSTL, ...
Servers, RAID Systems
Distributed Power Systems
Synchronous Buck with General Purpose Boost
TYPICAL APPLICATIO
SHDN
V
REF
LTC3718
I
ON
V
OUT
C
SS
0.1µF
V
FB1
PGOOD
SW1
SENSE
+
PGND1
SENSE
–
RUN/SS
C1 820pF X7R
R
C
4.75k
I
TH
SGND1
SGND2
V
FB2
R
F1
12.1k
C
OUT
: SANYO POSCAP 4TPB470M
BG
INTV
CC
V
IN1
V
IN2
PGND2
SW2
R
F2
37.4k
BOOST
TG
D
B
CMDSH-3
C
B
0.33µF
M1
Si7440DP
C
IN1
22µF
×2
D1
B340A
V
IN
2.5V
R
ON
237k
L1 0.8µH
+
M2
Si7440DP
D2
B340A
C
OUT
470µF
×2
EFFICIENCY (%)
V
OUT
1.25V
±10A
C
IN2
4.7µF
V
IN
L2
4.7µH
D3
MBR0520
C
VCC1
10µF
L1: SUMIDA CEP125-0R8MC
L2: PANASONIC ELJPC4R7MF
3718 TA01
Figure 1. High Efficiency Bus Termination Supply without Auxiliary 5V Supply
3718fa
U
U
U
Efficiency vs Load Current
100
90
80
70
60
50
40
30
20
10
0
0.01
0.1
FIGURE 1 CIRCUIT
1
10
LOAD CURRENT (A)
100
3718 G05/TA01a
V
IN
= 2.5V
V
OUT
= 1.25V
1
LTC3718
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
RUN/SS
V
ON
PGOOD
V
RNG
I
TH
SGND1
I
ON
V
FB1
V
REF
1
2
3
4
5
6
7
8
9
24 BOOST
23 TG
22 SW1
21 SENSE
+
20 SENSE
–
19 PGND1
18 BG
17 INTV
CC
16 V
IN1
15 V
IN2
14 PGND2
13 SW2
Input Supply Voltage (V
IN2
) .......................10V to – 0.3V
Boosted Topside Driver Supply Voltage
(BOOST) ............................................... 42V to – 0.3V
V
IN1
, I
ON
, SW1 Voltage ............................. 36V to – 0.3V
RUN/SS, PGOOD Voltages ......................... 7V to – 0.3V
V
ON
, V
REF
, V
RNG
Voltages .......(INTV
CC
+ 0.3V) to – 0.3V
I
TH
, V
FB1
Voltages .................................... 2.7V to – 0.3V
SW2 Voltage ............................................. 36V to – 0.4V
V
FB2
Voltage ................................................. V
IN2
+ 0.3V
SHDN Voltage ......................................................... 10V
TG, BG, INTV
CC
Peak Currents .................................. 2A
TG, BG, INTV
CC
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
ORDER PART
NUMBER
LTC3718EG
SHDN 10
SGND2 11
V
FB2
12
G PACKAGE
24-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 130°C/ W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
SYMBOL
Buck Regulator
I
Q(VIN1)
Input DC Supply Current (V
IN1
)
Normal
Shutdown Supply Current
Feedback Voltage Accuracy
Feedback Voltage Line Regulation
Feedback Voltage Load Regulation
Error Amplifier Transconductance
On-Time
Minimum On-Time
Minimum Off-Time
Maximum Current Sense Threshold
V
PGND
– V
SW1
(Source)
Minimum Current Sense Threshold
V
PGND
– V
SW1
(Sink)
Output Overvoltage Fault Threshold
Output Undervoltage Fault Threshold
RUN Pin Start Threshold
RUN Pin Latchoff Enable
PARAMETER
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specifications are T
A
= 25°C. V
IN1
= 15V, V
IN2
= 1.5V unless otherwise noted.
CONDITIONS
MIN
TYP
MAX
UNITS
V
RUN/SS
= 0V
I
TH
= 1.2V (Note 3)
V
IN1
= 4V to 36V, I
TH
= 1.2V (Note 3)
I
TH
= 0.5V to 1.9V (Note 3)
I
TH
= 1.2V (Note 3)
I
ON
= 60µA, V
ON
= 1.5V
I
ON
= 30µA, V
ON
= 1.5V
I
ON
= 180µA
V
RNG
= 1V, V
FB1
= V
REF
/2 – 50mV
V
RNG
= 0V, V
FB1
= V
REF
/2 – 50mV
V
RNG
= INTV
CC
, V
FB1
= V
REF
/2 – 50mV
V
RNG
= 1V, V
FB1
= V
REF
/2 + 50mV
V
RNG
= 0V, V
FB1
= V
REF
/2 + 50mV
V
RNG
= INTV
CC
, V
FB1
= V
REF
/2 + 50mV
q
q
q
q
q
1000
15
– 0.65
0.1
0.002
– 0.05
0.93
200
400
1.13
250
500
50
300
108
76
148
–140
–97
– 200
8
q
2000
30
0.65
– 0.3
1.33
300
600
100
400
162
114
222
–190
–133
– 270
12
2
4.5
V
FB1
∆V
FB1(LINE)
∆V
FB1(LOAD)
g
m(EA)
t
ON
t
ON(MIN)
t
OFF(MIN)
V
SENSE(MAX)
135
95
185
–165
–115
– 235
10
– 25
1.5
4
V
SENSE(MIN)
∆V
FB1(OV)
∆V
FB1(UV)
V
RUN/SS(ON)
V
RUN/SS(LE)
0.8
RUN/SS Pin Rising
2
U
µA
µA
%
%/V
%
mS
ns
ns
ns
ns
mV
mV
mV
mV
mV
mV
%
%
V
V
3718fa
W
U
U
W W
W
LTC3718
ELECTRICAL CHARACTERISTICS
SYMBOL
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
V
INTVCC
∆V
LDO(LOAD)
PGOOD Output
∆V
FB1H
∆V
FB1L
∆V
FB1(HYS)
V
PGL
Boost Regulator
V
IN2(MIN)
V
IN2(MAX)
I
Q(VIN2)
Minimum Operating Voltage
Maximum Operating Voltage
Input DC Supply Current (V
IN2
)
Normal
Shutdown Supply Current
V
FB2
Feedback Voltage
V
FB2
Pin Bias Current
Boost Reference Line Regulation
BOOST Switching Frequency
BOOST Maximum Duty Cycle
BOOST Switch Current Limit
BOOST Switch V
CESAT
BOOST Switch Leakage Current
SHDN Input Voltage High
SHDN Input Voltage Low
SHDN Pin Bias Current
PGOOD Upper Threshold
PGOOD Lower Threshold
PGOOD Hysterisis
PGOOD Low Voltage
PARAMETER
RUN Pin Latchoff Threshold
Soft-Start Charge Current
Soft-Start Discharge Current
V
IN1
Undervoltage Lockout
TG Driver Pull-Up On Resistance
TG Driver Pull-Down On Resistance
BG Driver Pull-Up On Resistance
BG Driver Pull-Down On Resistance
TG Rise Time
TG Fall Time
BG Rise Time
BG Fall Time
Internal V
CC
Voltage
Internal V
CC
Load Regulation
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specifications are T
A
= 25°C. V
IN1
= 15V, V
IN2
= 1.5V unless otherwise noted.
CONDITIONS
RUN/SS Pin Falling
V
RUN/SS
= 0V
V
RUN/SS
= 4.5V, V
FB
= 0V
V
IN
Falling
V
IN
Rising
TG High
TG Low
BG High
BG Low
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF
6V < V
IN1
<30V
I
CC
= 0mA to 20mA
V
FB1
= Rising
V
FB1
= Falling
V
FB1
= Returning
I
PGOOD
= 5mA
8
–8
q
q
q
MIN
– 0.5
0.8
TYP
3.5
–1.2
1.8
3.4
3.5
2
2
3
1
20
20
20
20
MAX
4.2
–3
3
3.9
4.0
3
3
4
2
UNITS
V
µA
µA
V
V
Ω
Ω
Ω
Ω
ns
ns
ns
ns
Internal V
CC
Regulator
4.7
5
– 0.1
10
–10
1
0.15
0.9
5.3
±2
12
–12
2
0.4
1.5
10
3
0.01
q
V
%
%
%
%
V
V
V
mA
µA
V
V
nA
%/V
MHz
MHz
%
mA
V
SHDN
=0V
0°C < T < 70°C
q
4.5
1
1.255
1.26
80
0.2
1.8
1.9
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
1.205
1.20
1.23
1.23
27
0.02
1.5V < V
IN2
< 10V
0°C < T < 70°C
q
1.0
0.9
82
500
1.4
1.4
86
800
300
0.01
(Note 5)
I
SW
= 300mA
V
SW
= 5V
350
1
0.3
mV
µA
V
V
µA
µA
1
V
SHDN
= 3V
V
SHDN
= 0V
25
0.01
50
0.1
3718fa
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LTC3718
ELECTRICAL CHARACTERISTICS
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
as follows:
LTC3718EG: T
J
= T
A
+ (P
D
• 130°C/W)
Note 3:
The LTC3718 is tested in a feedback loop that adjusts V
FB1
to
achieve a specified error amplifier output voltage (I
TH
).
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.
TYPICAL PERFOR A CE CHARACTERISTICS
Boost Converter Oscillator
Frequency vs Temperature
2.00
1.75
V
IN
= 5V
SHDN PIN BIAS CURRENT (µA)
40
50
T
A
= 25°C
SWITCHING FREQUENCY (MHz)
CURRENT LIMIT (mA)
1.50
1.25
1.00
0.75
0.50
0.25
0
–50
V
IN
= 1.5V
–25
0
25
50
TEMPERATURE (°C)
V
FB2
, Feedback Pin Voltage
1.25
100
90
FEEDBACK PIN VOLTAGE (V)
1.24
EFFICIENCY (%)
1.23
60
50
40
30
V
OUT
/V
IN
(%)
1.22
1.21
FIGURE 1 CIRCUIT
1.20
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
3718 G04
4
U W
75
SHDN Pin Current vs V
SHDN
1000
900
800
Boost Converter Current Limit
vs Duty Cycle
70°C
700
600
500
400
300
–40°C
25°C
30
20
10
0
100
3718 G01
0
1
2
3
4
SHDN PIN VOLTAGE (V)
5
3718 G02
200
10
20
30
40
50
60
DUTY CYCLE (%)
70
80
3718 G03
Efficiency vs Load Current
50.00
V
IN
= 2.5V
V
OUT
= 1.25V
V
OUT
/V
IN
Tracking Ratio vs Input
Voltage
49.95
49.90
LOAD = 1A
49.85
LOAD = 10A
49.80
49.75
49.70
LOAD = 0A
80
70
20
10
0
0.01
0.1
FIGURE 1 CIRCUIT
1
10
LOAD CURRENT (A)
100
3718 G05/TA01a
FIGURE 1 CIRCUIT
49.65
1.5
1.7
1.9 2.1 2.3 2.5
INPUT VOLTAGE (V)
2.7
2.9
3718 G06
3718fa
LTC3718
TYPICAL PERFOR A CE CHARACTERISTICS
Frequency vs Input Voltage
450
400
350
FREQUENCY (kHz)
∆V
OUT
/V
OUT
(%)
300
250
200
150
100
50
0
1.5
1.7
1.9 2.1 2.3 2.5
INPUT VOLTAGE (V)
2.7
2.9
3718 G07
V
OUT
= 1.25V
FIGURE 1 CIRCUIT
Load-Step Transient
V
OUT
200mV/DIV
I
L
5A/DIV
V
IN
= 2.5V
20µs/DIV
V
OUT
= 1.25V
LOAD = 500mA TO 10A STEP
FIGURE 1 CIRCUIT
On-Time vs V
ON
Voltage
1000
I
ION
= 30µA
800
ON-TIME (ns)
600
ON-TIME (ns)
150
100
400
ON-TIME (ns)
200
0
0
2
1
V
ON
VOLTAGE (V)
U W
3718 G11
Load Regulation
0
V
IN
= 2.5V
V
OUT
= 1.25V
LOAD = 10A
–0.1
–0.2
–0.3
–0.4
–0.5
FIGURE 1 CIRCUIT
–0.6
0
1
2
LOAD = 0A
3 4 5 6 7
LOAD CURRENT (A)
8
9
10
3718 G08
Start-Up Response
V
OUT
1V/DIV
I
L
2A/DIV
3718 G10.eps
V
IN
= 2.5V
4ms/DIV
V
OUT
= 1.25V
LOAD = 0.2Ω
FIGURE 1 CIRCUIT
3718 G09.eps
On-Time vs Temperature
300
250
200
1k
10k
I
ION
= 30µA
On-Time vs I
ON
Current
V
VON
= 0V
100
50
0
–50 –25
10
50
25
75
0
TEMPERATURE (°C)
100
125
1
10
I
ON
CURRENT (µA)
100
3718 G13
3
3718 G12
3718fa
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