FEATURES
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LTC3707
High Efficiency, 2-Phase
Synchronous Step-Down
Switching Regulator
DESCRIPTION
The LTC
®
3707 is a high performance dual step-down
switching regulator controller that drives N-channel
synchronous power MOSFET stages. A constant frequency
current mode architecture allows adjustment of the
frequency 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 3.5V to 30V 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.
L,
LT, LTC, LTM, Burst Mode, and OPTI-LOOP are registered trademarks of Linear Technology
Corporation. All other trademarks are the property of their respective owners. Protected by U.S.
Patents including 5481178, 5705919, 5929620, 6144194, 6177787, 6304066, 6580258.
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180° Phased Dual Controllers Reduce Required
Input Capacitance and Power Supply Induced Noise
OPTI-LOOP
®
Compensation Minimizes C
OUT
±1.5%
Output Voltage Accuracy over Temperature
Dual N-Channel MOSFET Synchronous Drive
Power Good Output Voltage Monitor
DC Programmed 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
Selectable Constant Frequency, Burst Mode
®
Operation or PWM Operation
Small 28-Lead Narrow SSOP Package
Notebook and Palmtop Computers, PDAs
Battery Chargers
Portable Instruments
Battery-Operated Digital Devices
DC Power Distribution Systems
APPLICATIONS
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TYPICAL APPLICATION
M1
L1
6.3μH
+
4.7μF
D3
V
IN
TG1
C
B1
, 0.1μF
BOOST1
SW1
INTV
CC
TG2
BOOST2
SW2
LTC3707
BG2
PGND
SENSE2
+
1000pF
SENSE1
–
V
OSENSE1
SENSE2
–
V
OSENSE2
I
TH2
RUN/SS2
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
BG1
SGND
M4
D2
SENSE1
+
R
SENSE1
0.01Ω
V
OUT1
5V
5A
1000pF
R
SENSE2
0.01Ω
V
OUT2
3.3V
5A
C
OUT
56μF
6V
SP
+
C
OUT1
47μF
6V
SP
R2
105k
1%
R1
20k
1%
C
C1
220pF
R
C1
15k
I
TH1
RUN/SS1
C
SS1
0.1μF
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
3707fb
1
LTC3707
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
RUN/SS1
SENSE1
+
SENSE1
–
V
OSENSE1
FREQSET
STBYMD
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
FREQSET, STBYMD, 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
= 95°C/W
ORDER INFORMATION
LEAD FREE FINISH
LTC3707EGN#PBF
LTC3707IGN#PBF
LEAD BASED FINISH
LTC3707EGN
LTC3707IGN
TAPE AND REEL
LTC3707EGN#TRPBF
LTC3707IGN#TRPBF
TAPE AND REEL
LTC3707EGN#TR
LTC3707IGN#TR
PART MARKING
3707EGN
3707IGN
PART MARKING
3707EGN
3707IGN
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
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/
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.
SYMBOL
V
OSENSE1, 2
I
OSENSE1, 2
V
REFLNREG
V
LOADREG
PARAMETER
Regulated Feedback Voltage
Feedback Current
Reference Voltage Line Regulation
Output Voltage Load Regulation
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
ELECTRICAL CHARACTERISTICS
MIN
0.788
TYP
0.800
–5
0.002
0.1
–0.1
1.3
MAX UNITS
0.812
–50
0.02
0.5
–0.5
V
nA
%/V
%
%
mmho
3707fb
g
m1,2
Transconductance Amplifier g
m
2
LTC3707
The
cations which apply over the
ELECTRICAL CHARACTERISTICS
25°C. V
l
denotesVthe specifi= 5V unless otherwise noted. full operating
temperature range, otherwise specifications are at T =
= 15V,
A
IN
RUN/SS1, 2
SYMBOL
g
mGBW1, 2
I
Q
PARAMETER
Transconductance Amplifier GBW
Input DC Supply Current
Normal Mode
Standby
Shutdown
Forced Continuous Threshold
Forced Continuous Pin Current
Burst Inhibit (Constant Frequency)
Threshold
Undervoltage Lockout
Feedback Overvoltage Lockout
Sense Pins Total Source Current
Master Shutdown Threshold
Keep-Alive Power On-Threshold
Maximum Duty Factor
Soft-Start Charge Current
RUN/SS Pin Latchoff Arming
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
Oscillator Frequency
Lowest Frequency
CONDITIONS
I
TH1, 2
= 1.2V; (Note 4)
(Note 5)
EXTV
CC
Tied to V
OUT1
= 5V
V
RUN/SS1, 2
= 0V, V
STBYMD
> 2V
V
RUN.SS1, 2
= 0V, V
STBYMD
= Open
l
MIN
TYP
3
350
125
20
MAX UNITS
MHz
μA
μA
μA
V
μA
V
V
V
μA
V
2
V
%
μA
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
5.2
2.0
200
V
%
mV
V
V
250
160
kHz
kHz
3707fb
35
0.84
–0.1
4.8
4
0.88
V
FCB
I
FCB
V
BINHIBIT
UVLO
V
OVL
I
SENSE
V
STBYMD MS
V
STBYMD
KA
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
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
V
STBYMD
Ramping Down
V
STBYMD
Ramping Up, RUN
SS1, 2
= 0V
In Dropout
V
RUN/SS1, 2
= 1.9V
V
RUN/SS1,
V
RUN/SS2,
Rising
V
RUN/SS1,
V
RUN/SS2,
Rising from 3V
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
OSENSE1
–
, 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
EXTCC
= 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
3.5
0.84
–90
0.4
98
0.5
1.0
0.86
–60
0.6
1.5
99.4
1.2
1.5
4.1
0.5
2
1.6
65
62
75
75
60
60
50
50
80
80
180
4.8
5.0
0.2
100
4.5
4.7
0.2
V
RUN/SS1, 2
ON RUN/SS Pin ON Threshold
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
Oscillator
f
OSC
f
LOW
INTV
CC
Linear Regulator
V
FREQSET
= Open (Note 8)
V
FREQSET
= 0V
190
120
220
140
3
LTC3707
The
cations which apply over the
ELECTRICAL CHARACTERISTICS
25°C. V
l
denotesVthe specifi= 5V unless otherwise noted. full operating
= 15V,
temperature range, otherwise specifications are at T =
A
IN
RUN/SS1, 2
SYMBOL
f
HIGH
I
FREQSET
V
3.3OUT
V
3.3IL
V
3.3VL
PGOOD Output
V
PGL
I
PGOOD
V
PG
PARAMETER
Highest Frequency
FREQSET Input Current
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
CONDITIONS
V
FREQSET
= 2.4V
V
FREQSET
= 0V
No Load
I
3.3
= 0 to 10mA
6V < V
IN
< 30V
I
PGOOD
= 2mA
V
PGOOD
= 5V
V
OSENSE
Respect to Set Output Voltage
V
OSENSE
Ramping Negative
V
OSENSE
Ramping Positive
l
MIN
280
TYP
310
–2
MAX UNITS
360
–1
3.45
2
0.2
0.3
1
kHz
μA
V
%
%
V
μA
%
%
3.3V Linear Regulator
3.20
3.35
0.5
0.05
0.1
–6
6
–7.5
7.5
–9.5
9.5
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 is guaranteed to meet performance specifications
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 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 formula:
LTC3707EGN = T
J
= T
A
+ (P
D
• 85°C/W)
Note 4:
The LTC3707 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 IC minimum on-time is tested under an ideal condition
without external power FETs. It can be different when the IC is working in
an actual circuit. See Minimum On-Time Considerations in the Application
Information section.
Note 8:
V
FREQSET
pin internally tied to a 1.19V reference through a
large resistance.
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Output Current
and Mode (Figure 13)
100
Burst Mode
90 OPERATION
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
= 15V
V
OUT
= 5V
100
V
IN
= 7V
90
EFFICIENCY (%)
V
IN
= 10V
V
IN
= 15V
V
IN
= 20V
70
Efficiency vs Input Voltage
(Figure 13)
90
FORCED
CONTINUOUS
MODE (PWM)
CONSTANT
FREQUENCY
(BURST DISABLE)
80
80
70
60
60
V
OUT
= 5V
I
OUT
= 3A
50
0.001
0.1
0.01
1
OUTPUT CURRENT (A)
50
10
3707 G02
5
15
INPUT VOLTAGE (V)
25
30
3707 G03
3707fb
4
LTC3707
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
50
STANDBY
SHUTDOWN
0
EXTV
CC
SWITCHOVER THRESHOLD
0
0
5
20
15
10
INPUT VOLTAGE (V)
25
30
3707 G04
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 Reg
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)
0
1
3
4
2
COMMON MODE VOLTAGE (V)
5
3707 G11
Current Sense Threshold
vs I
TH
Voltage
70
60
50
40
30
20
10
0
–10
–20
–30
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
0.5
1
1.5
V
ITH
(V)
2
2.5
3707 G12
3707fb
5
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