FEATURES
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LTC3727LX-1
High Efficiency, 2-Phase
Synchronous Step-Down
Switching Regulator
DESCRIPTIO
The LTC
®
3727LX-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.
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 28V (32V maximum)
input supply range encompasses all battery chemistries.
Table 1
PART
NUMBER
LTC3727
LTC3727-1
LTC3727A-1
V
IN
RANGE
4V to 36V
4V to 36V
4V to 36V
V
REF
ACCURACY
OVERTEMPERATURE
±1.5%
±1%
±1%
±1%
LATCH-
OFF
No
Yes
No
No
MINIMUM
ON-TIME
120ns
180ns
180ns
120ns
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
±1.5%
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 32V 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 and 5mm
×
5mm QFN Packages
LTC3727LX-1 4V to 32V
APPLICATIO S
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Telecom Systems
Automotive Systems
Distributed DC Power Systems
, LT, LTC and LTM 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.
TYPICAL APPLICATIO
+
4.7µF
V
IN
PGOOD INTV
CC
M1
0.1µF
TG1
BOOST1
SW1
BG1
PLLIN
SENSE1
+
0.015Ω
V
OUT1
5V
5A
1000pF
SENSE1
105k
1%
–
1µF
CERAMIC
M3
0.1µF
TG2
BOOST2
SW2
LTC3727LX-1
BG2
PGND
SENSE2
+
1000pF
SENSE2
–
V
OSENSE2
I
TH2
220pF
15k
8µH
M2
V
OSENSE1
I
TH1
20k
1%
220pF
15k
+
47µF
6V
SP
M1, M2, M3, M4: FDS6680A
RUN/SS1 SGND RUN/SS2
0.1µF
0.1µF
Figure 1. High Efficiency Dual 12V/5V Step-Down Converter
3727lx1fa
U
U
U
V
IN
18V TO 28V
22µF
50V
CERAMIC
15µH
M4
0.015Ω
V
OUT2
12V
4A
280k
1%
20k
1%
+
56µF
15V
SP
3727LX1 F01
1
LTC3727LX-1
ABSOLUTE
AXI U
RATI GS
(Note 1)
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 125°C
Lead Temperature
(Soldering, 10 sec, G Package)............................. 300°C
Solder Reflow Temperature (UH Package) ........... 265°C
Input Supply Voltage (V
IN
).........................32V to – 0.3V
Top Side Driver Voltages
(BOOST1, BOOST2) ...................................40V to – 0.3V
Switch Voltage (SW1, SW2) .........................32V 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
PACKAGE/ORDER I FOR ATIO
TOP VIEW
RUN/SS1
SENSE1
+
SENSE1
–
RUN/SS1
SENSE1
–
SENSE1
+
2
3
4
5
6
7
8
9
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
LTC3727LXEG-1
V
OSENSE1
1
PLLFLTR 2
PLLIN 3
FCB 4
I
TH1
5
SGND 6
3.3V
OUT
7
I
TH2
8
SW1
TG1
1
NC
NC
28 PGOOD
PGOOD
ORDER PART
NUMBER
V
OSENSE1
PLLFLTR
PLLIN
FCB
I
TH1
SGND
3.3V
OUT
10
I
TH2
11
V
OSENSE2
12
SENSE2
–
13
SENSE2
+
14
V
OSENSE2
NC
TG2
SENSE2
–
SENSE2
+
G PACKAGE
28-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 95°C/W
UH PACKAGE
32-LEAD (5mm
×
5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 34°C/W
EXPOSED PAD (PIN 33) IS SGND
(MUST BE SOLDERED TO PCB)
Order Options
Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking:
http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
●
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
VOSENSE1, 2
V
REFLNREG
PARAMETER
Regulated Feedback Voltage
Feedback Current
Reference Voltage Line Regulation
CONDITIONS
(Note 4); I
TH1, 2
Voltage = 1.2V
(Note 4)
V
IN
= 3.6V to 30V (Note 4)
●
ELECTRICAL CHARACTERISTICS
RUN/SS2
SW2
NC
Main Control Loops
0.788
0.800
–5
0.002
0.812
– 50
0.02
V
nA
%/V
3727lx1fa
2
U
U
W
W W
U
W
TOP VIEW
ORDER PART
NUMBER
LTC3727LXEUH-1
24 BOOST1
23 V
IN
22 BG1
21 EXTV
CC
20 INTV
CC
19 PGND
18 BG2
17 BOOST2
32 31 30 29 28 27 26 25
33
UH PART
MARKING
727LX1
9 10 11 12 13 14 15 16
MIN
TYP
MAX
UNITS
LTC3727LX-1
The
●
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
LOADREG
PARAMETER
Output Voltage Load Regulation
CONDITIONS
(Note 4)
Measured in Servo Loop;
∆I
TH
Voltage = 1.2V to 0.7V
Measured in Servo Loop;
∆I
TH
Voltage = 1.2V to 2.0V
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
●
●
●
ELECTRICAL CHARACTERISTICS
MIN
TYP
0.1
– 0.1
1.3
3
1
20
MAX
0.5
– 0.5
UNITS
%
%
mmho
MHz
mA
µA
V
µA
V
V
V
µA
%
µA
g
m1, 2
g
mGBW1, 2
I
Q
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
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
Phase Detector Output Current
Sinking Capability
Sourcing Capability
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
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
C
LOAD
= 3300pF Each Driver
C
LOAD
= 3300pF Each Driver
●
●
●
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
INTV
CC
Linear Regulator
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
●
7.2
7.5
0.2
70
7.8
1.0
160
V
%
mV
V
V
6.9
7.3
0.3
Oscillator and Phase-Locked Loop
V
PLLFLTR
= 1.2V
V
PLLFLTR
= 0V
V
PLLFLTR
≥
2.4V
350
220
460
380
255
530
100
f
PLLIN
< f
OSC
f
PLLIN
> f
OSC
–15
15
430
290
580
kHz
kHz
kHz
kΩ
µA
µA
3727lx1fa
3
LTC3727LX-1
The
●
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
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
CONDITIONS
No Load
I
3.3
= 0mA to 10mA
6V < V
IN
< 30V
●
ELECTRICAL CHARACTERISTICS
3.3V Linear Regulator
MIN
3.25
TYP
3.35
0.5
0.05
MAX
3.45
2.5
0.3
UNITS
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 LTC3727LX-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.
Note 3:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formulas:
LTC3727LXEG-1: T
J
= T
A
+ (P
D
• 95
°C/W)
LTC3727LXEUH-1: T
J
= T
A
+ (P
D
• 34
°C/W)
Note 4:
The LTC3727LX-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.
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs Output Current
and Mode (Figure 13)
100
90
80
Burst Mode
OPERATION
FORCED
CONTINUOUS
MODE
EFFICIENCY (%)
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
3727LX1 G01
EFFICIENCY (%)
EFFICIENCY (%)
70
CONSTANT-
FREQUENCY
(BURST DISABLE)
4
U W
Efficiency vs Output Current
(Figure 13)
100
V
IN
= 7V
90
V
IN
= 10V
V
IN
= 15V
V
IN
= 20V
70
90
100
Efficiency vs Input Voltage
(Figure 13)
V
OUT
= 5V
I
OUT
= 3A
80
80
70
60
V
OUT
= 5V
0.1
0.01
1
OUTPUT CURRENT (A)
10
3727LX1 G02
60
50
0.001
50
5
25
15
INPUT VOLTAGE (V)
32
3727LX1 G03
3727lx1fa
LTC3727LX-1
TYPICAL PERFOR A CE CHARACTERISTICS
Supply Current vs Input Voltage
and Mode (Figure 13)
1000
EXTV
CC
VOLTAGE DROP (mV)
800
SUPPLY CURRENT (µA)
INTV
CC
VOLTAGE (V)
BOTH
CONTROLLERS ON
600
400
200
SHUTDOWN
0
0
20
10
INPUT VOLTAGE (V)
30 32
3727LX1 G04
Maximum Current Sense Threshold
vs Duty Factor
150
125
100
V
SENSE
(mV)
75
50
25
0
0
20
40
60
DUTY FACTOR (%)
80
100
3727LX1 G07
V
SENSE
(mV)
90
75
60
45
30
15
0
V
SENSE
(mV)
Current Sense Threshold
vs I
TH
Voltage
150
125
0.0
V
SENSE
(mV)
75
50
25
0
–25
–50
0
0.5
1.0
1.5
V
ITH
(V)
2.0
2.5
NORMALIZED V
OUT
(%)
100
–0.2
V
ITH
(V)
U W
3727LX1 G10
EXTV
CC
Voltage Drop
160
140
120
100
80
60
40
20
0
0
Internal 7.5V LDO Line Regulation
7.7
7.6
7.5
7.4
7.3
7.2
7.1
7.0
6.9
I
LOAD
= 1mA
V
EXTVCC
= 8.5V
10
30
CURRENT (mA)
20
40
50
3727LX1 G05
6.8
0
5
10
15
20
25
INPUT VOLTAGE (V)
30 32
3727LX1 G06
Maximum Current Sense Threshold
vs Percent of Nominal Output
Voltage (Foldback)
150
135
120
105
Maximum Current Sense Threshold
vs V
RUN/SS
(Soft-Start)
150
V
SENSE(CM)
= 1.6V
125
100
75
50
20
60
80
0
100
40
PERCENT OF NOMINAL OUTPUT VOLTAGE (%)
3727LX1 G08
0
1
2
3
4
V
RUN/SS
(V)
5
6
3727LX1 G09
Load Regulation
FCB = 0V
V
IN
= 15V
FIGURE 1
V
ITH
vs V
RUN/SS
2.5
V
OSENSE
= 0.7V
–0.1
2.0
1.5
1.0
–0.3
0.5
–0.4
0
1
3
2
LOAD CURRENT (A)
0
4
5
3727LX1 G11
0
1
2
3
V
RUN/SS
(V)
4
5
6
3727LX1 G12
3727lx1fa
5
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