FEATURES
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LTC3727A-1
High Efficiency, 2-Phase
Synchronous Step-Down
Switching Regulators
DESCRIPTION
The LTC
®
3727A-1 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 550kHz. Power loss and noise due to the ESR of
the input capacitors are minimized by operating the two
controller output stages out of phase.
The LTC3727A-1 is an improved version of the LTC3727
family of parts. It has smaller output ripple while in the
drop-out condition and shorter minimum on-time.
OPTI-LOOP compensation allows the transient response to
be optimized over a wide range of output capacitance and
ESR values. There is a precision 0.8V reference and a power
good output indicator. A wide 4V to 30V (36V maximum)
input supply range encompasses all battery chemistries.
A RUN/SS pin for each controller provides soft-start. Current
foldback limits MOSFET heat dissipation during short-circuit
conditions. Output overvoltage protection circuitry protects
the controller until V
OUT
returns to normal.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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, 5929620, 6177787, 6144194, 6100678,
5408150, 6580258, 6304066, 5705919.
Wide Output Voltage Range: 0.8V ≤ V
OUT
≤ 14V
Out-of-Phase Controllers Reduce Required Input
Capacitance and Power Supply Induced Noise
OPTI-LOOP
®
Compensation Minimizes C
OUT
±
1% Output Voltage Accuracy
Power Good Output Voltage Monitor
Phase-Lockable Fixed Frequency 250kHz to 550kHz
Dual N-Channel MOSFET Synchronous Drive
Wide V
IN
Range: 4V to 36V Operation
Very Low Dropout Operation: 99% Duty Cycle
Adjustable Soft-Start Current Ramping
Foldback Output Current Limiting
Output Overvoltage Protection
Low Shutdown I
Q
: 20μA
Selectable Constant Frequency or Burst Mode
®
Operation
Small 28-Lead SSOP Package
APPLICATIONS
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Telecom Systems
Automotive Systems
Battery-Operated Digital Devices
TYPICAL APPLICATION
+
4.7μF
M1
8μH
0.1μF
M2
V
IN
PGOOD INTV
CC
TG1
TG2
BOOST1
SW1
BG1
PLLIN
SENSE1
+
0.015Ω
V
OUT1
5V
5A
1000pF
SENSE1
–
V
OSENSE1
105k
1%
I
TH1
20k
1%
220pF
15k
SENSE2
–
V
OSENSE2
I
TH2
220pF
15k
20k
1%
280k
1%
LTC3727A-1
BOOST2
SW2
BG2
PGND
SENSE2
+
1000pF
M4
1μF
CERAMIC
M3
0.1μF
22μF
50V
CERAMIC
V
IN
18V TO 28V
15μH
0.015Ω
V
OUT2
12V
4A
+
47μF
6V
SP
M1, M2, M3, M4: FDS6680A
RUN/SS1 SGND RUN/SS2
0.1μF
0.1μF
+
56μF
15V
SP
3727 F01
Figure 1. High Efficiency Dual 12V/5V Step-Down Converter
3727a1fa
1
LTC3727A-1
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
) ......................... 36V to –0.3V
Top Side Driver Voltages
BOOST1, BOOST2.................................. 42V to –0.3V
Switch Voltage (SW1, SW2) ......................... 36V to –5V
INTV
CC
, EXTV
CC
, (BOOST1-SW1),
(BOOST2-SW2)......................................... 8.5V to –0.3V
RUN/SS1, RUN/SS2, PGOOD ...................... 7V to –0.3V
SENSE1
+
, SENSE2
+
, SENSE1
–
,
SENSE2
–
Voltages ..................................... 14V to –0.3V
PLLIN, PLLFLTR, FCB Voltages ............ 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 ................................. 50mA
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
G PACKAGE
28-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 95°C/W
ORDER INFORMATION
LEAD FREE FINISH
LTC3727AEG-1#PBF
LTC3727AIG-1#PBF
LEAD BASED FINISH
LTC3727AEG-1
LTC3727AIG-1
TAPE AND REEL
LTC3727AEG-1#TRPBF
LTC3727AIG-1#TRPBF
TAPE AND REEL
LTC3727AEG-1#TR
LTC3727AIG-1#TR
PART MARKING
LTC3727AEG-1
LTC3727AIG-1
PART MARKING
LTC3727AEG-1
LTC3727AIG-1
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/
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
l
l
l
MIN
0.792
TYP
0.800
–5
0.002
0.1
–0.1
MAX
0.808
–50
0.02
0.5
–0.5
UNITS
V
nA
%/V
%
%
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LTC3727A-1
ELECTRICAL CHARACTERISTICS
SYMBOL
g
m1, 2
g
mGBW1, 2
I
Q
PARAMETER
Transconductance Amplifier g
m
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
Maximum Current Sense Threshold
TG Transition Time:
Rise Time
Fall Time
BG Transition Time:
Rise Time
Fall Time
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
V
OSENSE1, 2
= 0.7V, V
SENSE1–, 2–
= 12V
(Note 6)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
(Note 6)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
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; Sink/Source 5μA (Note 4)
I
TH1, 2
= 1.2V (Note 4)
(Note 5)
V
IN
= 15V, EXTV
CC
Tied to V
OUT1
, V
OUT1
= 8.5V
V
RUN/SS1, 2
= 0V
l
MIN
TYP
1.3
3
670
20
MAX
UNITS
mmho
MHz
μA
μA
V
μA
V
V
V
μA
%
μA
35
0.84
–0.05
7.3
4
0.88
V
FCB
I
FCB
V
BINHIBIT
UVLO
V
OVL
I
SENSE
DF
MAX
I
RUN/SS1, 2
V
SENSE(MAX)
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
I
PLLFLTR
0.76
–0.30
0.800
–0.18
6.8
3.5
0.84
–85
98
0.5
1.0
105
0.86
–60
99.4
1.2
1.5
135
50
50
40
40
90
90
120
V
RUN/SS1, 2
ON RUN/SS Pin ON Threshold
1.9
165
90
90
90
80
V
mV
ns
ns
ns
ns
ns
ns
ns
Top Gate Off to Bottom Gate On Delay C
LOAD
= 3300pF Each Driver
Synchronous Switch-On Delay Time
Bottom Gate Off to Top Gate On Delay C
LOAD
= 3300pF Each Driver
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
Phase Detector Output Current
Sinking Capability
Sourcing Capability
f
PLLIN
< f
OSC
f
PLLIN
> f
OSC
V
PLLFLTR
= 1.2V
V
PLLFLTR
= 0V
V
PLLFLTR
≥ 2.4V
350
220
460
Tested with a Square Wave (Note 7)
8.5V < V
IN
< 30V, V
EXTVCC
= 6V
I
CC
= 0mA to 20mA, V
EXTVCC
= 6V
I
CC
= 20mA, V
EXTVCC
= 8.5V
I
CC
= 20mA, EXTV
CC
Ramping Positive
l
INTV
CC
Linear Regulator
7.2
7.5
0.2
70
6.9
7.3
0.3
380
255
530
100
–15
15
430
290
580
7.8
1.0
160
V
%
mV
V
V
kHz
kHz
kHz
kΩ
μA
μA
Oscillator and Phase-Locked Loop
3727a1fa
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LTC3727A-1
ELECTRICAL CHARACTERISTICS
SYMBOL
V
3.3OUT
V
3.3IL
V
3.3VL
PGOOD Output
V
PGL
I
PGOOD
V
PG
PGOOD Voltage Low
PGOOD Leakage Current
PGOOD Trip Level, Either Controller
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
0.1
0.3
±1
–9.5
9.5
V
μA
%
%
PARAMETER
3.3V Regulator Output Voltage
3.3V Regulator Load Regulation
3.3V Regulator Line Regulation
3.3V Linear Regulator
No Load
I
3.3
= 0mA to 10mA
6V < V
IN
< 30V
3.25
3.35
0.5
0.05
3.45
2.5
0.3
V
%
%
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
MIN
TYP
MAX
UNITS
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 LTC3727AE-1 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 LTC3727AI-1 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:
LTC3727AG-1: T
J
= T
A
+ (P
D
• 95 °C/W)
Note 4:
The LTC3727A-1 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 (%)
70
60
50
40
30
20
10
0
0.001
V
IN
= 15V
V
OUT
= 8.5V
0.1
0.01
1
OUTPUT CURRENT (A)
10
3727 G01
Efficiency vs Output Current
(Figure 13)
100
V
IN
= 7V
100
Efficiency vs Input Voltage
(Figure 13)
V
OUT
= 5V
I
OUT
= 3A
Burst Mode
OPERATION
FORCED
CONTINUOUS
MODE
90
EFFICIENCY (%)
EFFICIENCY (%)
V
OUT
= 5V
0.1
0.01
1
OUTPUT CURRENT (A)
10
3727 G02
90
V
IN
= 10V
V
IN
= 15V
V
IN
= 20V
80
80
CONSTANT
FREQUENCY
(BURST DISABLE)
70
70
60
60
50
0.001
50
5
25
15
INPUT VOLTAGE (V)
35
3727 G03
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LTC3727A-1
TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current vs Input Voltage
and Mode (Figure 13)
1000
160
140
EXTV
CC
VOLTAGE DROP (mV)
800
SUPPLY CURRENT (μA)
BOTH
CONTROLLERS ON
600
120
INTV
CC
VOLTAGE (V)
100
80
60
40
20
SHUTDOWN
0
0
20
10
INPUT VOLTAGE (V)
30
3727 G04
EXTV
CC
Voltage Drop
V
EXTVCC
= 8.5V
7.7
7.6
7.5
7.4
7.3
7.2
7.1
7.0
6.9
0
10
30
CURRENT (mA)
20
40
50
3727 G05
Internal 7.5V LDO Line Regulation
I
LOAD
= 1mA
400
200
0
6.8
0
5
10
15
20
25
INPUT VOLTAGE (V)
30
35
3727 G06
Maximum Current Sense Threshold
vs Duty Factor
150
125
100
75
50
25
0
0
20
40
60
DUTY FACTOR (%)
80
100
3727 G07
Maximum Current Sense Threshold
vs Percent of Nominal Output
Voltage (Foldback)
150
135
120
105
V
SENSE
(mV)
90
75
60
45
30
15
0
50
20
60
0
80
100
40
PERCENT OF NOMINAL OUTPUT VOLTAGE (%)
3727 G08
Maximum Current Sense Threshold
vs V
RUN/SS
(Soft-Start)
150
V
SENSE(CM)
= 1.6V
125
V
SENSE
(mV)
V
SENSE
(mV)
100
75
0
1
2
3
V
RUN/SS
(V)
4
5
6
3727 G09
Current Sense Threshold
vs I
TH
Voltage
150
125
NORMALIZED V
OUT
(%)
100
V
SENSE
(mV)
75
50
25
0
–25
–50
–0.4
0
0.5
1.0
1.5
V
ITH
(V)
2.0
2.5
3727 G10
Load Regulation
0.0
FCB = 0V
V
IN
= 15V
FIGURE 1
2.5
V
ITH
vs V
RUN/SS
V
OSENSE
= 0.7V
–0.1
2.0
–0.2
V
ITH
(V)
0
1
3
2
LOAD CURRENT (A)
4
5
3727 G11
1.5
1.0
–0.3
0.5
0
0
1
2
3
V
RUN/SS
(V)
4
5
6
3727 G12
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