LTC3717-1
Wide Operating Range,
No R
SENSE
TM
Step-Down Controller
for DDR/QDR Memory Termination
FEATURES
s
s
DESCRIPTIO
s
s
s
s
s
s
s
s
s
s
s
s
s
s
V
OUT
= 1/2 V
REF
Adjustable and Symmetrical Sink/Source
Current Limit up to 20A
True Current Mode Control with Optional Use of
Sense Resistor
V
ON
and I
ON
Pins Allow Constant Frequency
Operation During Input and Output Voltage Changes
±0.65%
Output Voltage Accuracy
Up to 97% Efficiency
Ultrafast Transient Response
2% to 90% Duty Cycle at 200kHz
t
ON(MIN)
≤
100ns
Stable with Ceramic C
OUT
Power Good Output Voltage Monitor
Wide V
IN
Range: 4V to 36V
Adjustable Switching Frequency up to 1.5MHz
Output Overvoltage Protection
Optional Short-Circuit Shutdown Timer
Available in a 5mm
×
5mm QFN Package
The LTC
®
3717-1 is a synchronous step-down switching
regulator controller for double data rate (DDR) and Quad
Data Rate
TM
(QDR
TM
) memory termination. The controller
uses a valley current control architecture to deliver very
low duty cycles with or without a sense resistor. Operating
frequency is selected by an external resistor and is com-
pensated for variations in V
IN
and V
OUT
.
Forced continuous operation reduces noise and RF inter-
ference. Output voltage is internally set to half of V
REF
,
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 accom-
plished 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
CC
input.
, LTC and LT are registered trademarks 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, Hitachi, IDT, Micron Technology, Inc. and Samsung.
APPLICATIO S
s
s
s
Bus Termination: DDR and QDR Memory, SSTL,
HSTL, ...
Notebook Computers, Desktop Servers
Tracking/Margining Power Supply
TYPICAL APPLICATIO
V
CC
5V TO 28V
1µF
0.1µF
V
CC
I
ON
V
REF
RUN/SS
TG
LTC3717-1
SW
SENSE
+
I
TH
BOOST
SGND
V
ON
PGOOD
DRV
CC
INTV
CC
BG
715k
V
DD
= 2.5V
Si7840DP
B320A
+
V
IN
2.5V TO 5.5V
150µF
6.3V
×2
EFFICIENCY (%)
100
90
80
70
60
50
40
30
20
10
V
IN
= 5V
V
IN
= 2.5V
470pF
20k
0.22µF
CMDSH-3
Si7840DP
4.7µF
0.68µH
+
V
OUT
1.25V
180µF
±10A
4V
×2
+
B320A
PGND
SENSE
–
V
FB
37171 F01a
0
Figure 1. High Efficiency DDR Memory Termination Supply
U
Efficiency vs Load Current
V
OUT
= 1.25V
0
2
4
6
8
10
LOAD CURRENT (A)
12
14
37171 F01b
U
U
sn37171 37171fs
1
LTC3717-1
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
Boosted Topside Driver Supply Voltage
(BOOST) ............................................... 42V to – 0.3V
V
IN
, I
ON
, SW, SENSE
+
Voltage .................. 36V to – 0.3V
EXTV
CC
, DRV
CC
, RUN/SS, PGOOD,
(BOOST – SW) Voltages ............................ 7V to – 0.3V
V
ON
, V
REF
, V
RNG
Voltages .......(INTV
CC
+ 0.3V) to – 0.3V
I
TH
, V
FB
Voltages...................................... 2.7V to – 0.3V
TG, BG, INTV
CC
, EXTV
CC
, DRV
CC
Peak Currents ....... 2A
TG, BG, INTV
CC
, EXTV
CC
, DRV
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 125°C
Reflow Peak Body Temperature ............................ 260°C
RUN/SS
BOOST
NC
NC
NC
NC
32 31 30 29 28 27 26 25
V
ON
1
PGOOD 2
V
RNG
3
I
TH
4
SGND 5
I
ON
6
V
FB
7
NC 8
9 10 11 12 13 14 15 16
33
24 SW
23 SENSE
+
22 NC
21 SENSE
–
20 PGND
19 BG
18 DRV
CC
17 INTV
CC
NC
UH PACKAGE
32-LEAD (5mm
×
5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 34°C/ W
EXPOSED PAD IS SGND (PIN 33) MUST BE SOLDERED TO PCB
ORDER PART NUMBER
LTC3717EUH-1
QFN PART MARKING
37171
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
SYMBOL
Buck Regulator
I
Q(VIN)
Input DC Supply Current (V
IN
)
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
SW
(Source)
Minimum Current Sense Threshold
V
PGND
– V
SW
(Sink)
PARAMETER
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specifications are T
A
= 25°C. V
IN
= 15V, unless otherwise noted.
CONDITIONS
MIN
TYP
MAX
UNITS
EXTV
CC
V
REF
V
IN
NC
NC
NC
NC
NC
TG
V
RUN/SS
= 0V
I
TH
= 1.2V (Note 3), V
REF
= 2.4V
V
IN
= 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
= 30µA, V
ON
= 0V
I
ON
= 60µA, V
ON
= 0V
I
ON
= 180µA
V
RNG
= 1V, V
FB
= V
REF
/2 – 50mV
V
RNG
= 0V, V
FB
= V
REF
/2 – 50mV
V
RNG
= INTV
CC
, V
FB
= V
REF
/2 – 50mV
V
RNG
= 1V, V
FB
= V
REF
/2 + 50mV
V
RNG
= 0V, V
FB
= V
REF
/2 + 50mV
V
RNG
= INTV
CC
, V
FB
= V
REF
/2 + 50mV
q
q
q
q
q
q
q
q
1000
15
– 0.65
0.1
0.002
– 0.05
0.93
186
95
1.13
233
115
50
300
108
76
148
–140
–97
– 200
135
95
185
–165
–115
– 235
2000
30
0.65
– 0.3
1.33
280
135
100
400
162
114
222
–190
–133
– 270
V
FB
∆V
FB(LINE)
∆V
FB(LOAD)
g
m(EA)
t
ON
t
ON(MIN)
t
OFF(MIN)
V
SENSE(MAX)
V
SENSE(MIN)
sn37171 37171fs
2
U
µA
µA
%
%/V
%
mS
ns
ns
ns
ns
mV
mV
mV
mV
mV
mV
W
U
U
W W
W
LTC3717-1
ELECTRICAL CHARACTERISTICS
SYMBOL
∆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)
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
EXTVCC
∆V
EXTVCC
∆V
EXTVCC(HYS)
PGOOD Output
∆V
FBH
∆V
FBL
∆V
FB(HYS)
V
PGL
PGOOD Upper Threshold
PGOOD Lower Threshold
PGOOD Hysteresis
PGOOD Low Voltage
PARAMETER
Output Overvoltage Fault Threshold
Output Undervoltage Threshold
RUN Pin Start Threshold
RUN Pin Latchoff Enable
RUN Pin Latchoff Threshold
Soft-Start Charge Current
Soft-Start Discharge Current
V
IN
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
EXTV
CC
Switchover Voltage
EXTV
CC
Switch Drop Voltage
EXTV
CC
Switchover Hysteresis
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specifications are T
A
= 25°C. V
IN
= 15V, unless otherwise noted.
CONDITIONS
MIN
8
q
TYP
10
– 25
1.5
4
3.5
MAX
12
2
4.5
4.2
–3
3
3.9
4.0
UNITS
%
%
V
V
V
µA
µA
V
V
Ω
Ω
Ω
Ω
ns
ns
ns
ns
0.8
RUN/SS Pin Rising
RUN/SS Pin Falling
V
RUN/SS
= 0V
V
RUN/SS
= 4.5V, V
FB
= 0V
V
IN
Falling
V
IN
Rising
TG High (Note 5)
TG Low (Note 5)
BG High (Note 5)
BG Low (Note 5)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF
6V < V
CC
< 30V, V
EXTVCC
= 4V
I
CC
= 0mA to 20mA, V
EXTVCC
= 4V
I
CC
= 20mA, V
EXTVCC
Rising
I
CC
= 20mA, V
EXTVCC
= 5V
q
q
q
q
– 0.5
0.8
–1.2
1.8
3.4
3.5
2
2
3
1
20
20
20
20
Internal V
CC
Regulator
4.7
4.5
5
– 0.1
4.7
150
200
V
FB
Rising (0% = 1/3 V
REF
)
V
FB
Falling (0% = 1/3 V
REF
)
V
FB
Returning (0% = 1/3 V
REF
)
I
PGOOD
= 5mA
8
–8
10
– 10
1
0.15
12
– 12
2
0.4
300
5.3
±2
V
%
V
mV
mV
%
%
%
V
∆V
LDO(LOADREG)
Internal V
CC
Load Regulation
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:
LTC3717EUH-1: T
J
= T
A
+ (P
D
• 34°C/W)
Note 3:
The LTC3717EUH-1 is tested in a feedback loop that adjusts V
FB
to
achieve a specified error amplifier output voltage (I
TH
).
Note 4:
The LTC3717EUH-1 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
DS(ON)
limit guaranteed by design and/or correlation to static
test.
sn37171 37171fs
3
LTC3717-1
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs Load Current
100
90
80
FREQUENCY (kHz)
70
EFFICIENCY (%)
V
IN
= 2.5V
V
OUT
= 1.25V
60
50
40
30
20
10
0
0.01
0.1
V
OUT
/V
IN
(%)
FIGURE 1 CIRCUIT
1
10
LOAD CURRENT (A)
100
37171 G01
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
Load Regulation
0
–0.1
V
IN
= 2.5V
V
OUT
= 1.25V
1000
∆V
OUT
/V
OUT
(%)
ON-TIME (ns)
600
–0.3
–0.4
–0.5
FIGURE 1 CIRCUIT
–0.6
0
1
2
3 4 5 6 7
LOAD CURRENT (A)
8
9
10
ON-TIME (ns)
–0.2
4
U W
37171 G04
V
OUT
/V
IN
Tracking Ratio
vs Input Voltage
50.00
49.95
49.90
LOAD = 1A
49.85
LOAD = 10A
49.80
49.75
49.70
FIGURE 1 CIRCUIT
49.65
1.5
1.7
1.9 2.1 2.3 2.5
INPUT VOLTAGE (V)
2.7
2.9
37171 G02
Frequency vs Input Voltage
450
400
350
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
37171 G03
LOAD = 0A
LOAD = 10A
LOAD = 0A
V
OUT
= 1.25V
FIGURE 1 CIRCUIT
Start-Up Response
V
OUT
1V/DIV
I
L
2A/DIV
37171 G05
V
IN
= 2.5V
4ms/DIV
V
OUT
= 1.25V
LOAD = 0.2Ω
FIGURE 1 CIRCUIT
37171 G06
On-Time vs V
ON
Voltage
I
ION
= 30µA
300
250
200
150
100
200
50
On-Time vs Temperature
I
ION
= 30µA
800
400
0
0
2
1
V
ON
VOLTAGE (V)
3
37171 G07
0
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
37171 G08
sn37171 37171fs
LTC3717-1
TYPICAL PERFOR A CE CHARACTERISTICS
On-Time vs I
ON
Current
10k
V
VON
= 0V
0
FCB PIN CURRENT (µA)
ON-TIME (ns)
1k
∆INTV
CC
(%)
100
10
1
10
I
ON
CURRENT (µA)
100
37171 G09
RUN/SS Latchoff Thresholds
vs Temperature
UNDERVOLTAGE LOCKOUT THRESHOLD (V)
5.0
4.0
MAXIMUM CURRENT SENSE THRESHOLD (mV)
RUN/SS THRESHOLD (V)
4.5
LATCHOFF ENABLE
4.0
3.5
LATCHOFF THRESHOLD
3.0
–50
–25
75
0
25
50
TEMPERATURE (°C)
Maximum Current Sense Threshold
vs RUN/SS Voltage, V
RNG
= 1V
MAXIMUM CURRENT SENSE THRESHOLD (mV)
MAXIMUM CURRENT SENSE THRESHOLD (mV)
160
140
120
100
80
60
40
20
0
2.0
2.2
2.4
2.6 2.8 3.0
RUN/SS (V)
3.2
3.4 3.6
37171 G15
100
80
60
40
20
0
–50 –30 –10 10 30 50 70 90 110 130
TEMPERATURE (°C)
37171 G16
gm (mS)
U W
100
37171 G12
INTV
CC
Load Regulation
3
RUN/SS Latchoff Thresholds
vs Temperature
–0.1
2
PULL-DOWN CURRENT
1
–0.2
–0.3
0
PULL-UP CURRENT
–1
–0.4
–0.5
0
10
30
40
20
INTV
CC
LOAD CURRENT (mA)
50
37171 G10
–2
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
37171 G11
Undervoltage Lockout Threshold
vs Temperature
300
250
200
150
100
50
Maximum Current Sense Threshold
vs V
RNG
Voltage
3.5
3.0
2.5
125
2.0
–50 –25
75
0
25
50
TEMPERATURE (C)
100
125
0
0.50
0.75
1.00
1.25 1.50
V
RNG
(V)
1.75
2.00
37171 G13
37171 G14
Maximum Current Sense Threshold
vs Temperature, V
RNG
= 1V
180
160
140
120
1.50
1.40
1.30
1.20
1.10
1.00
0.90
0.80
Error Amplifier gm
vs Temperature
0.70
–50 –30 –10 10 30 50 70 90 110 130
TEMPERATURE (°C)
37171 G17
sn37171 37171fs
5
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