FEATURES
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LTC3709
Fast 2-Phase, No R
SENSE
TM
,
Synchronous DC/DC Controller
with Tracking/Sequencing
DESCRIPTIO
The LTC
®
3709 is a single output, dual phase, synchronous
step-down switching regulator. The controller uses a
constant on-time, 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 input supply
voltage. An internal phase-locked loop allows the LTC3709
to be synchronized to an external clock.
A TRACK pin is provided for tracking or sequencing the
output voltage among several LTC3709 chips or an
LTC3709 and other DC/DC regulators. Soft-start is ac-
complished using an external timing capacitor.
Fault protection is provided by an output overvoltage com-
parator and an optional short-circuit shutdown timer. The
current limit level is user programmable. A wide supply
range allows voltages as high as 31V to step down to 0.6V.
, LTC and LT are registered trademarks of Linear Technology Corporation.
No RSENSE and PolyPhase are trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents, including 5481178, 6476589, 6144194, 5847554, 6177678,
6304066, 6580258, 6674274, 6462525, 6593724.
PolyPhase
TM
Valley Current Mode Controller
Synchronizable to an External Clock with PLL
Coincident or Ratiometric Tracking
Sense Resistor Optional
2% to 90% Duty Cycle at 200kHz
t
ON(MIN)
< 100ns
True Remote Sensing Differential Amplifier
High Efficiency at Both Light and Heavy Loads
Power Good Output Voltage Monitor
0.6V
±1%
Reference
Adjustable Current Limit
Programmable Soft-Start and Operating Frequency
Output Overvoltage Protection
Optional Short-Circuit Shutdown Timer
32-Lead (5mm
×
5mm) QFN Package
APPLICATIO S
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Notebook Computers
Power Supply for DSP, ASIC, Graphic Processors
TYPICAL APPLICATIO
5V
4.7µF
1µF
47.5k
V
CC
DRV
CC
I
ON
TRACK
TG1
V
RNG
FCB
BOOST1
100k
0.1µF
PGOOD
RUN/SS
3.32k
100nF
680pF
20k
SGND
10k
V
FB
DIFFOUT
15k
V
OS–
V
OS+
TG2
BOOST2
SW2
SENSE2
+
BG2
SENSE2
–
PGND2
SW1
SENSE1
+
10Ω
324k
High Efficiency Dual Phase 1.5V/30A Step-Down Converter
1µF
1µF
PGND1
PGND2
10µF
35V
×3
HAT2168H
0.22µF
1.22µH
100
95
90
V
IN
4.5V TO 28V
10k
EFFICIENCY (%)
BG1
HAT2165H
EXTLPF
SENSE1
–
INTLPF
PGND1
I
TH
LTC3709
HAT2168H
0.22µF
V
IN
1.22µH
V
OUT
1.5V
30A
HAT2165H
+
330µF
2.5V
×4
3709 TA01a
U
U
U
Efficiency and Power Loss
V
IN
= 12V
10
9
8
EFFICIENCY
7
6
5
4
3
POWER LOSS
2
1
0.1
1
10
LOAD CURRENT (A)
0
100
3709 TA01b
85
80
75
70
65
60
55
50
0.01
POWER LOSS (W)
3709f
1
LTC3709
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
Input Supply Voltage (V
CC
, DRV
CC
) ............ 7V to – 0.3V
Boosted Topside Driver Supply Voltage
(BOOST1, BOOST2) .................................. 37V to – 0.3V
Switch Voltage (SW1, 2) ............................. 31V to – 1V
SENSE1
+
, SENSE2
+
Voltages ....................... 31V to – 1V
SENSE1
–
, SENSE2
–
Voltages .................... 10V to – 0.3V
I
ON
Voltage ............................................... 31V to –0.3V
(BOOST – SW) Voltages ..............................7V to – 0.3V
RUN/SS, PGOOD Voltages .......................... 7V to – 0.3V
TRACK Voltage ............................................7V to – 0.3V
V
RNG
Voltage ................................. V
CC
+ 0.3V to – 0.3V
I
TH
Voltage ............................................... 2.7V to – 0.3V
V
FB
Voltage .............................................. 2.7V to – 0.3V
INTLPF, EXTLPF Voltages ........................ 2.7V to – 0.3V
V
OS+
, V
OS–
Voltages ................................... 7V to – 0.3V
FCB Voltage ................................................ 7V to – 0.3V
Operating Temperature Range ................ – 40°C to 85°C
Junction Temperature (Note 2) ............................ 125°C
Storage Temperature Range ................ – 65°C to 125°C
32 31 30 29 28 27 26 25
RUN/SS 1
I
TH
2
V
FB
3
TRACK 4
SGND 5
SGND 6
V
OS
–
SENSE1
+
BOOST1
PGOOD
V
RNG
SW1
TG1
FCB
I
ON
24 SENSE1
–
23 PGND1
22 BG1
33
21 DRV
CC
20 BG2
19 PGND2
18 SENSE2
–
17 V
CC
9 10 11 12 13 14 15 16
7
DIFFOUT 8
V
OS+
NC
TG2
SW2
UH PACKAGE
32-LEAD (5mm
×
5mm) PLASTIC QFN
EXPOSED PAD IS SGND (PIN 33)
MUST BE SOLDERED TO PCB
T
JMAX
= 125°C,
θ
JA
= 34°C/ W
ORDER PART NUMBER
LTC3709EUH
UH PART MARKING
3709
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
SYMBOL
I
Q
PARAMETER
Input DC Supply Current
Normal
Shutdown
FB Pin Input Current
Feedback Voltage
Feedback Voltage Line Regulation
Feedback Voltage Load Regulation
Error Amplifier Transconductance
On-Time
Minimum On-Time
Minimum Off-Time
Main Control Loop
The
●
denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= DRV
CC
= 5V, unless otherwise noted.
CONDITIONS
MIN
TYP
MAX
UNITS
2.4
25
I
TH
= 1.2V (Note 3)
I
TH
= 1.2V (Note 3)
V
IN
= 4V to 6.5V (Note 3)
I
TH
= 0.5V to 2V (Note 3)
I
TH
= 1.2V (Note 3)
V
IN
= 20V, I
ON
= 180µA
V
IN
= 20V, I
ON
= 90µA
V
IN
= 20V, I
ON
= 540µA
V
IN
= 20V, I
ON
= 90µA
1.3
90
180
●
SENSE2
+
EXTLPF
INTLPF
BOOST2
3
65
– 60
0.606
– 0.2
1.6
140
280
100
350
I
FB
V
FB
∆V
FB(LINEREG)
∆V
FB(LOADREG)
g
m(EA)
t
ON
t
ON(MIN)
t
OFF(MIN)
– 35
0.594
0.600
0.02
– 0.12
1.45
116
233
45
250
2
U
mA
µA
nA
V
%/V
%
mS
ns
ns
ns
ns
3709f
W
U
U
W W
W
LTC3709
ELECTRICAL CHARACTERISTICS
SYMBOL
V
SENSE(MAX)
PARAMETER
Maximum Current Sense Threshold
The
●
denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= DRV
CC
= 5V, unless otherwise noted.
CONDITIONS
V
RNG
= 1V
V
RNG
= 0V
V
RNG
= V
CC
V
RNG
= 1V
V
RNG
= 0V
V
RNG
= V
CC
8.5
– 8.5
●
MIN
124
86
177
TYP
144
101
202
– 60
– 40
– 80
10
– 10
1.4
3
2.3
MAX
166
119
234
UNITS
mV
mV
mV
mV
mV
mV
V
SENSE(MIN)
Minimum Current Sense Threshold
∆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)
UVLO
TG R
UP
TG R
DOWN
BG R
UP
BG R
DOWN
Tracking
I
TRACK
V
FB(TRACK)
Overvoltage Fault Threshold
Undervoltage Fault Threshold
RUN Pin Start Threshold
RUN Pin Latchoff Enable Threshold
RUN Pin Latchoff Threshold
Soft-Start Charge Current
Soft-Start Discharge Current
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
TRACK Pin Input Current
Feedback Voltage at Tracking
Measured at V
CC
Pin
TG High
TG Low
BG High
BG Low
I
TH
= 1.2V, V
TRACK
= 0.2V (Note 3)
V
TRACK
= 0.1V, I
TH
= 1.2V (Note 3)
V
TRACK
= 0.3V, I
TH
= 1.2V (Note 3)
V
TRACK
= 0.5V, I
TH
= 1.2V (Note 3)
V
FB
Rising
V
FB
Falling
V
FB
Falling
V
FB
Returning
V
PGOOD
= 7V
I
PGOOD
= 5mA
RUN/SS Pin Rising
RUN/SS Pin Falling
12.5
– 12.5
2
%
%
V
V
V
0.8
– 0.5
0.8
– 1.2
2
3.9
2
1.5
3
1.5
–100
–3
4
4.2
µA
µA
V
Ω
Ω
Ω
Ω
–150
110
310
510
12.5
– 12.5
nA
mV
mV
mV
%
%
µs
%
90
290
490
8.5
– 8.5
100
100
300
500
10
– 10
3.5
PGOOD Output
∆V
FBH
∆V
FBL
PG Delay
∆V
FB(HYS)
I
PGOOD
V
PGL
Phase-Lock Loop
I
INTPLL_SOURCE
I
INTPLL_SINK
I
EXTPLL_SOURCE
I
EXTPLL_SINK
V
FCB(DC)
V
FCB(AC)
t
ON(PLL)1
Internal PLL Sourcing Current
Internal PLL Sinking Current
External PLL Sourcing Current
External PLL Sinking Current
Forced Continuous Threshold
Clock Input Threshold
t
ON1
Modulation Range by External PLL
Up Modulation
Down Modulation
t
ON2
Modulation Range by Internal PLL
Up Modulation
Down Modulation
Measured with a DC Voltage at FCB Pin
Measured with a AC Pulse at FCB Pin
I
ON1
= 180µA, V
EXTPLL
= 1.8V
I
ON1
= 180µA, V
EXTPLL
= 0.6V
I
ON2
= 180µA, V
INTPLL
= 1.8V
I
ON2
= 180µA, V
INTPLL
= 0.6V
1.9
1
186
20
– 20
20
– 20
2.1
1.5
233
58
233
58
2.3
2
µA
µA
µA
µA
V
V
ns
ns
ns
ns
PGOOD Upper Threshold
PGOOD Lower Threshold
PGOOD Delay
PGOOD Hysteresis
PGOOD Leakage Current
PGOOD Low Voltage
±1
0.2
0.4
µA
V
80
t
ON(PLL)2
186
80
3709f
3
LTC3709
ELECTRICAL CHARACTERISTICS
SYMBOL
A
V
V
OS
CM
CMRR
I
CL
GBP
SR
V
O(MAX)
R
IN
PARAMETER
Differential Gain
Input Offset Voltage
Common Mode Input Voltage Range
Common Mode Rejection Ratio
Output Current
Gain Bandwidth Product
Slew Rate
Maximum High Output Voltage
Input Resistance
Differential Amplifier
The
●
denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= DRV
CC
= 5V, unless otherwise noted.
CONDITIONS
MIN
0.995
= 1mA,
Input Referred; Gain = 1
I
OUT
= 1mA
0V < IN
+
= IN
–
< 5V, I
OUT
= 1mA,
Input Referred
I
OUT
= 1mA
R
L
= 2k
I
OUT
= 1mA
Measured at IN
+
Pin
IN
+
= IN
–
= 1.2V, I
OUT
TYP
1.000
0.5
MAX
1.005
7
5
70
UNITS
V/V
mV
V
dB
mA
MHz
V/µs
V
kΩ
0
45
10
40
2
5
V
CC
– 1.2 V
CC
– 0.8
80
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:
LTC3709EUH: T
J
= T
A
+ (P
D
• 34°C/W)
Note 3:
The LTC3709 is tested in a feedback loop that adjusts V
FB
to
achieve a specified error amplifier output voltage (I
TH
).
Note 4:
The LTC3709E 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 is guaranteed by design and/or correlation to static
test.
3709f
4
LTC3709
TYPICAL PERFOR A CE CHARACTERISTICS
Start-Up
V
RUN/SS
5V/DIV
V
OUT
1V/DIV
SW1
5V/DIV
SW2
5V/DIV
I
L1
10A/DIV
I
L2
10A/DIV
1ms/DIV
Transient Response (CCM)
I
LOAD
3A-18A
V
OUT
50mV/DIV
V
SW1
20V/DIV
V
SW2
20V/DIV
20µs/DIV
3709 G04
EFFICIENCY (%)
Power Loss vs Load Current
10
V
IN
= 12V
V
OUT
= 1.5V
f = 220kHz
1
POWER LOSS (W)
95
EFFICIENCY (%)
QUIESCENT CURRENT (mA)
0.1
0.01
0.001
10
1000
10000
100
LOAD CURRENT (mA)
100000
3709 G07
U W
Continuous Current Mode (CCM)
Discontinuous Current Mode (DCM)
SW1
5V/DIV
SW2
1V/DIV
3709 G01
2µs/DIV
3709 G02
10µs/DIV
3709 G03
Transient Response (DCM)
100
I
LOAD
3A-18A
V
OUT
50mV/DIV
V
SW1
20V/DIV
V
SW2
20V/DIV
20µs/DIV
3709 G05
Efficiency vs Load Current
V
IN
= 12V
95 V
OUT
= 1.5V
f = 220kHz
90
85
80
75
70
65
60
55
50
10
100
1000
LOAD (mA)
10000
100000
3709 G06
Efficiency vs V
IN
100
3.0
Quiescent Current at V
CC
= 5V
V
OUT
= 1.5V
I
LOAD
= 10A
f = 220kHz
2.8
2.6
90
2.4
85
2.2
80
4
8
12
16
V
IN
(V)
20
24
3709 G08
2.0
–40
–20
40
20
0
TEMPERATURE (°C)
60
80
3709 G09
3709f
5
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