FEATURES
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LTC3707-SYNC
High Efficiency, 2-Phase
Synchronous Step-Down Switching Regulator
DESCRIPTION
The LTC
®
3707-SYNC is a high performance dual step-down
switching regulator controller that drives all N-channel
synchronous power MOSFET stages. A constant frequency
current mode architecture allows phase-lockable frequency
of up to 300kHz. Power loss and noise due to the ESR of
the input capacitors are minimized by operating the two
controller output stages out of phase.
OPTI-LOOP compensation allows the transient response to
be optimized over a wide range of output capacitance and
ESR values. The precision 0.8V reference and power good
output indicator are compatible with future microprocessor
generations, and a wide 4.5V to 28V (30V maximum) input
supply range encompasses all battery chemistries.
A RUN/SS pin for each controller provides both soft-
start and optional timed, short-circuit shutdown. Current
foldback limits MOSFET dissipation during short-circuit
conditions when overcurrent latchoff is disabled. Output
overvoltage protection circuitry latches on the bottom
MOSFET until V
OUT
returns to normal. The FCB mode
pin can select among Burst Mode operation, constant
frequency mode and continuous inductor current mode
or regulate a secondary winding. The IC includes a power
good output pin that indicates when both outputs are within
7.5% of their designed set point.
L,
LT, LTC and LTM are registered trademarks of Linear Technology Corporation. Burst Mode
and OPTI-LOOP are registered trademarks of Linear Technology Corporation. Protected by U.S.
Patents including 5481178, 5705919, 5929620, 6144194, 6177787, 6304066, 6580258.
180° Phased Controllers Reduce Required Input
Capacitance and Power Supply Induced Noise
OPTI-LOOP
®
Compensation Minimizes C
OUT
Dual N-Channel MOSFET Synchronous Drive
±1.5%
Output Voltage Accuracy
Power Good Output Voltage Monitor
Phase-Lockable Fixed Frequency 150kHz to 300kHz
Wide V
IN
Range: 4.5V to 28V Operation
Very Low Dropout Operation: 99% Duty Cycle
Adjustable Soft-Start Current Ramping
Foldback Output Current Limiting
Latched Short-Circuit Shutdown with Defeat Option
Output Overvoltage Protection
Remote Output Voltage Sense
Low Shutdown I
Q
: 20μA
5V and 3.3V Standby Regulators
Small 28-Lead Narrow SSOP Package (0.150˝ Wide)
Selectable Constant Frequency, Burst Mode
®
or
PWM Operation
APPLICATIONS
n
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Notebook and Palmtop Computers, PDAs
Telecom Systems
Portable Instruments
Battery-Operated Digital Devices
DC Power Distribution Systems
TYPICAL APPLICATION
M1
L1
6.3μH
+
4.7μF
D3
V
IN
PGOOD INTV
CC
TG1
TG2
C
B1
, 0.1μF
BOOST1
SW1
BG1
f
IN
LTC3707-SYNC
BOOST2
SW2
BG2
PGND
SENSE2
+
1000pF
SENSE1
–
V
OSENSE1
SENSE2
–
V
OSENSE2
I
TH2
C
SS2
0.1μF
C
C2
220pF
R
C2
15k
D4
1μF
CERAMIC
M3
C
B2
, 0.1μF
V
IN
5.2V TO 28V
C
IN
22μF
50V
CERAMIC
L2
6.3μH
D1
M2
M4
D2
PLLIN
SENSE1
+
R
SENSE1
0.01Ω
V
OUT1
5V
5A
1000pF
R
SENSE2
0.01Ω
V
OUT2
3.3V
5A
C
OUT
56mμF
6V
SP
+
C
OUT1
47μF
6V
SP
R2
105k
1%
R1
20k
1%
C
C1
220pF
R
C1
15k
I
TH1
C
SS1
0.1μF
RUN/SS1 SGND RUN/SS2
R3
20k
1%
R4
63.4k
1%
+
M1, M2, M3, M4: FDS6680A
3707 F01
Figure 1. High Efficiency Dual 5V/3.3V Step-Down Converter
3707sfa
1
LTC3707-SYNC
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
RUN/SS1
SENSE1
+
SENSE1
–
V
OSENSE1
PLLFLTR
PLLIN
FCB
I
TH1
SGND
1
2
3
4
5
6
7
8
9
28 PGOOD
27 TG1
26 SW1
25 BOOST1
24 V
IN
23 BG1
22 EXTV
CC
21 INTV
CC
20 PGND
19 BG2
18 BOOST2
17 SW2
16 TG2
15 RUN/SS2
Input Supply Voltage (V
IN
) ......................... 30V to –0.3V
Top Side Driver Voltages
(BOOST1, BOOST2) ................................... 36V to –0.3V
Switch Voltage (SW1, SW2) ......................... 30V to –5V
INTV
CC
, EXTV
CC
, RUN/SS1, RUN/SS2, (BOOST1-SW1),
(BOOST2-SW2), PGOOD.............................. 7V to –0.3V
SENSE1
+
, SENSE2
+
, SENSE1
–
,
SENSE2
–
Voltages .........................(1.1)INTV
CC
to –0.3V
PLLIN, PLLFLTR, FCB, Voltage ............. INTV
CC
to –0.3V
I
TH1
, I
TH2
, V
OSENSE1
, V
OSENSE2
Voltages ... 2.7V to –0.3V
Peak Output Current <10μs (TG1, TG2, BG1, BG2) .....3A
INTV
CC
Peak Output Current ................................. 40mA
Operating Temperature Range (Note 2).... –40°C to 85°C
Junction Temperature (Note 3) ............................. 125°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec) .................. 300°C
3.3V
OUT
10
I
TH2
11
V
OSENSE2
12
SENSE2
–
13
SENSE2
+
14
GN PACKAGE
28-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 80°C/W
ORDER INFORMATION
LEAD FREE FINISH
LTC3707EGN-SYNC#PBF
LTC3707IGN-SYNC#PBF
LEAD BASED FINISH
LTC3707EGN-SYNC
LTC3707IGN-SYNC
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
28-Lead Plastic SSOP
28-Lead Plastic SSOP
PACKAGE DESCRIPTION
28-Lead Plastic SSOP
28-Lead Plastic SSOP
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 85°C
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 85°C
LTC3707EGN-SYNC#TRPBF LTC3707EGN-SYNC
LTC3707IGN-SYNC#TRPBF LTC3707IGN-SYNC
TAPE AND REEL
LTC3707EGN-SYNC#TR
LTC3707IGN-SYNC#TR
PART MARKING
LTC3707EGN-SYNC
LTC3707IGN-SYNC
Consult LTC Marketing for parts specified with wider operating temperature ranges.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS
SYMBOL
V
OSENSE1, 2
I
VOSENSE1, 2
V
REFLNREG
V
LOADREG
PARAMETER
Regulated Feedback Voltage
Feedback Current
Reference Voltage Line Regulation
Output Voltage Load Regulation
Main Control Loops
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
RUN/SS1, 2
= 5V unless otherwise noted.
CONDITIONS
(Note 4); I
TH1, 2
Voltage = 1.2V
(Note 4)
V
IN
= 3.6V to 30V (Note 4)
(Note 4)
Measured in Servo Loop;
ΔI
TH
Voltage = 1.2V to 0.7V
Measured in Servo Loop;
ΔI
TH
Voltage = 1.2V to 2.0V
I
TH1, 2
= 1.2V; Sink/Source 5μA; (Note 4)
l
l
l
MIN
0.788
TYP
0.800
–5
0.002
0.1
–0.1
1.3
MAX
0.812
–50
0.02
0.5
–0.5
UNITS
V
nA
%/V
%
%
mmho
g
m1, 2
Transconductance Amplifier g
m
3707sfa
2
LTC3707-SYNC
ELECTRICAL CHARACTERISTICS
SYMBOL
g
mGBW1, 2
I
Q
PARAMETER
Transconductance Amplifier GBW
Input DC Supply Current
Normal Mode
Shutdown
Forced Continuous Threshold
Forced Continuous Pin Current
Burst Inhibit (Constant Frequency)
Threshold
Undervoltage Lockout
Feedback Overvoltage Lockout
Sense Pins Total Source Current
Maximum Duty Factor
Soft-Start Charge Current
V
FCB
= 0.85V
Measured at FCB pin
V
IN
Ramping Down
Measured at V
OSENSE1, 2
(Each Channel); V
SENSE1–, 2–
= V
SENSE1+, 2+
= 0V
In Dropout
V
RUN/SS1, 2
= 1.9V
V
RUN/SS1
, V
RUN/SS2
Rising
Soft Short Condition V
OSENSE1, 2
= 0.5V;
V
RUN/SS1, 2
= 4.5V
V
OSENSE1, 2
= 0.5V
V
OSENSE1, 2
= 0.7V,V
SENSE1–, 2–
= 5V
V
OSENSE1, 2
= 0.7V,V
SENSE1–, 2–
= 5V
(Note 6)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
(Note 6)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF Each Driver
C
LOAD
= 3300pF Each Driver
Tested with a Square Wave (Note 7)
6V < V
IN
< 30V, V
EXTVCC
= 4V
I
CC
= 0 to 20mA, V
EXTVCC
= 4V
I
CC
= 20mA, V
EXTVCC
= 5V
I
CC
= 20mA, EXTV
CC
Ramping Positive
l
l
l
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
RUN/SS1, 2
= 5V unless otherwise noted.
CONDITIONS
I
TH1, 2
= 1.2V; (Note 4)
(Note 5)
V
IN
= 15V; EXTV
CC
Tied to V
OUT1
; V
OUT1
= 5V
V
RUN/SS1, 2
= 0V, V
STBYMD
= Open
l
MIN
TYP
3
350
20
MAX
UNITS
MHz
μA
μA
V
μA
V
V
V
μA
%
μA
35
0.84
–0.1
4.8
4
0.88
V
FCB
I
FCB
V
BINHIBIT
UVLO
V
OVL
I
SENSE
DF
MAX
I
RUN/SS1, 2
V
RUN/SS1, 2
LT
I
SCL1, 2
I
SDLHO
V
SENSE(MAX)
0.76
–0.30
0.800
–0.18
4.3
3.5
0.84
–90
98
0.5
1.0
0.5
0.86
–60
99.4
1.2
1.5
4.1
2
1.6
V
RUN/SS1, 2
ON RUN/SS Pin ON Threshold
RUN/SS Discharge Current
Shutdown Latch Disable Current
Maximum Current Sense Threshold
TG Transition Time:
Rise Time
Fall Time
BG Transition Time:
Rise Time
Fall Time
Top Gate Off to Bottom Gate On Delay
Synchronous Switch-On Delay Time
Bottom Gate Off to Top Gate On Delay
Top Switch-On Delay Time
Minimum On-Time
Internal V
CC
Voltage
INTV
CC
Load Regulation
EXTV
CC
Voltage Drop
EXTV
CC
Switchover Voltage
EXTV
CC
Hysteresis
Nominal Frequency
Lowest Frequency
Highest Frequency
PLLIN Input Resistance
2.0
4.75
4
5
85
88
110
110
110
100
V
V
μA
μA
mV
mV
ns
ns
ns
ns
ns
ns
ns
RUN/SS Pin Latchoff Arming Threshold V
RUN/SS1
, V
RUN/SS2
Rising from 3V
65
62
75
75
60
60
50
50
80
80
180
TG1, 2 t
r
TG1, 2 t
f
BG1, 2 t
r
BG1, 2 t
f
TG/BG t
1D
BG/TG t
2D
t
ON(MIN)
V
INTVCC
V
LDO
INT
V
LDO
EXT
V
EXTVCC
V
LDOHYS
f
NOM
f
LOW
f
HIGH
R
PLLIN
INTV
CC
Linear Regulator
4.8
5.0
0.2
100
4.5
4.7
0.2
V
PLLFLTR
= 1.2V
V
PLLFLTR
= 0V
V
PLLFLTR
≥ 2.4V
190
120
280
220
140
310
50
250
160
360
5.2
2.0
200
V
%
mV
V
V
kHz
kHz
kHz
kΩ
Oscillator and Phase-Locked Loop
3707sfa
3
LTC3707-SYNC
ELECTRICAL CHARACTERISTICS
SYMBOL
I
PLLFLTR
PARAMETER
Phase Detector Output Current
Sinking Capability
Sourcing Capability
3.3V Regulator Output Voltage
3.3V Regulator Load Regulation
3.3V Regulator Line Regulation
PGOOD Voltage Low
PGOOD Leakage Current
PGOOD Trip Level, Either Controller
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
RUN/SS1, 2
= 5V unless otherwise noted.
CONDITIONS
f
PLLIN
< f
OSC
f
PLLIN
> f
OSC
No Load
I
3.3
= 0 to 10mA
6V < V
IN
< 30V
I
PGOOD
= 2mA
V
PGOOD
= 5V
V
OSENSE
with Respect to Set Output Voltage
V
OSENSE
Ramping Negative
V
OSENSE
Ramping Positive
–6
6
–7.5
7.5
l
MIN
TYP
–15
15
MAX
UNITS
μA
μA
3.3V Linear Regulator
V
3.3OUT
V
3.3IL
V
3.3VL
PGOOD Output
V
PGL
I
PGOOD
V
PG
0.1
0.3
±1
–9.5
9.5
V
μA
%
%
3.20
3.35
0.5
0.05
3.45
2
0.2
V
%
%
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
The LTC3707E-SYNC is guaranteed to meet performance
specification from 0°C to 85°C. Specifications over the –40°C to 85°C
operating temperature range are assured by design, characterization
and correlation with statistical process controls. The LTC3707I-SYNC
is guaranteed to meet performance specifications over the full –40°C
to 85°C operating temperature range.
Note 3:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formulas:
LTC3707-SYNC: T
J
= T
A
+ (P
D
• 95 °C/W)
Note 4:
The IC is tested in a feedback loop that servos V
ITH1, 2
to a
specified voltage and measures the resultant V
OSENSE1, 2
.
Note 5:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Applications Information.
Note 6:
Rise and fall times are measured using 10% and 90% levels.
Delay times are measured using 50% levels.
Note 7:
The minimum on-time condition is specified for an inductor
peak-to-peak ripple current ≥40% of I
MAX
(see minimum on-time
considerations in the Applications Information section).
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Output Current
and Mode (Figure 13)
100
90
80
EFFICIENCY (%)
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.001
0.1
0.01
1
OUTPUT CURRENT (A)
V
IN
= 15V
V
OUT
= 5V
10
3707 G01
Efficiency vs Output Current
(Figure 13)
100
V
IN
= 7V
90
EFFICIENCY (%)
90
V
IN
= 10V
V
IN
= 15V
V
IN
= 20V
70
100
Efficiency vs Input Voltage
(Figure 13)
Burst Mode
OPERATION
FORCED
CONTINUOUS
MODE
CONSTANT
FREQUENCY
(BURST DISABLE)
80
80
70
60
V
OUT
= 5V
0.1
0.01
1
OUTPUT CURRENT (A)
10
3707 G02
60
V
OUT
= 5V
I
OUT
= 3A
5
25
15
INPUT VOLTAGE (V)
35
3707 G03
50
0.001
50
3707sfa
4
LTC3707-SYNC
TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current vs Input Voltage
and Mode (Figure 13)
1000
200
INTV
CC
AND EXTV
CC
SWITCH VOLTAGE (V)
EXTV
CC
Voltage Drop
5.05
5.00
4.95
4.90
4.85
4.80
4.75
INTV
CC
and EXTV
CC
Switch
Voltage vs Temperature
INTV
CC
VOLTAGE
EXTV
CC
VOLTAGE DROP (mV)
800
SUPPLY CURRENT (μA)
150
600
BOTH
CONTROLLERS ON
400
100
200
SHUTDOWN
0
0
5
20
15
10
INPUT VOLTAGE (V)
25
30
3707 G04
50
EXTV
CC
SWITCHOVER THRESHOLD
0
0
10
20
CURRENT (mA)
30
40
3707 G05
4.70
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
3707 G06
Internal 5V LDO Line Regulation
5.1
5.0
INTV
CC
VOLTAGE (V)
4.9
4.8
4.7
4.6
4.5
4.4
0
5
20
15
10
INPUT VOLTAGE (V)
25
30
3707 G07
Maximum Current Sense Threshold
vs Duty Factor
75
80
70
60
V
SENSE
(mV)
0
20
40
60
DUTY FACTOR (%)
80
100
3707 G08
Maximum Current Sense Threshold
vs Percent of Nominal Output
Voltage (Foldback)
I
LOAD
= 1mA
V
SENSE
(mV)
50
50
40
30
20
10
25
0
0
50
100
0
25
75
PERCENT ON NOMINAL OUTPUT VOLTAGE (%)
3707 G09
Maximum Current Sense
Threshold vs V
RUN/SS
(Soft-Start)
80
V
SENSE(CM)
= 1.6V
80
Maximum Current Sense Threshold
vs Sense Common Mode Voltage
90
80
76
V
SENSE
(mV)
V
SENSE
(mV)
1
3
4
2
COMMON MODE VOLTAGE (V)
70
60
50
40
30
20
10
0
–10
–20
–30
Current Sense Threshold
vs I
TH
Voltage
60
V
SENSE
(mV)
72
40
68
20
64
0
0
1
2
3
V
RUN/SS
(V)
3707 G10
4
5
6
60
0
5
3707 G11
0
0.5
1
1.5
V
ITH
(V)
2
2.5
3707 G12
3707sfa
5
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