LTC3727/LTC3727-1
High Efficiency, 2-Phase
Synchronous Step-Down Switching Regulators
FEATURES
s
s
DESCRIPTIO
s
s
s
s
s
s
s
s
s
s
s
s
s
s
s
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
Latched Short-Circuit Shutdown (LTC3727 Only)
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
Small 28-Lead SSOP Package
LTC3727-1 Also Available in the 5mm
×
5mm QFN
Package
Selectable Constant Frequency or Burst Mode
®
Operation
The LTC
®
3727/LTC3727-1 are high performance dual
step-down switching regulator controllers that drive all
N-channel synchronous power MOSFET stages. A con-
stant 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 30V (36V maximum)
input supply range encompasses all battery chemistries.
A RUN/SS pin for each controller provides soft-start, and
on the LTC3727GN, optional timed, short-circuit shut-
down. Current foldback limits MOSFET heat 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, constant
frequency mode and continuous inductor current mode or
regulate a secondary winding. The LTC3727/LTC3727-1
include a power good output pin that indicates when both
outputs are within 7.5% of their designed set point.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode and OPTI-LOOP are registered trademarks of Linear Technology Corporation.
APPLICATIO S
s
s
s
Telecom Systems
Automotive Systems
Battery-Operated Digital Devices
TYPICAL APPLICATIO
8µH
+
4.7µF
V
IN
PGOOD INTV
CC
M1
0.1µF
M2
TG1
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
LTC3727/
LTC3727-1
TG2
BOOST2
SW2
BG2
PGND
SENSE2
+
1µF
CERAMIC
M3
0.1µF
1000pF
+
47µF
6V
SP
M1, M2, M3, M4: FDS6680A
RUN/SS1 SGND RUN/SS2
0.1µF
0.1µF
220pF
15k
Figure 1. High Efficiency Dual 12V/5V Step-Down Converter
U
V
IN
18V TO 28V
22µF
50V
CERAMIC
15µH
M4
0.015Ω
V
OUT2
12V
4A
280k
1%
20k
1%
U
U
+
56µF
15V
SP
1628 F01
3727f
1
LTC3727/LTC3727-1
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 150°C
Storage Temperature Range
(UH Package) ....................................... – 65°C to 125°C
Lead Temperature (Soldering, 10 sec).................. 300°C
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, Voltage ............ 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
V
OSENSE1
PLLFLTR
PLLIN
FCB
I
TH1
SGND
LTC3727EG
LTC3727EG-1
SW1
TG1
1
NC
NC
28 PGOOD
PGOOD
ORDER PART
NUMBER
V
OSENSE1
1
PLLFLTR 2
PLLIN 3
FCB 4
I
TH1
5
SGND 6
3.3V
OUT
7
I
TH2
8
3.3V
OUT
10
I
TH2
11
V
OSENSE2
12
SENSE2
–
13
SENSE2
+
14
V
OSENSE2
NC
SENSE2
–
SENSE2
+
TG2
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 IS SGND
(MUST BE SOLDERED TO PCB)
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
q
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
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;
∆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)
q
q
q
ELECTRICAL CHARACTERISTICS
RUN/SS2
SW2
NC
Main Control Loops
0.792
0.800
–5
0.002
0.1
– 0.1
1.3
0.808
– 50
0.02
0.5
– 0.5
V
nA
%/V
%
%
mmho
3727f
g
m1, 2
Transconductance Amplifier g
m
2
U
U
W
W W
U
W
TOP VIEW
ORDER PART
NUMBER
LTC3727EUH-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
UH PART
MARKING
37271
9 10 11 12 13 14 15 16
MIN
TYP
MAX
UNITS
LTC3727/LTC3727-1
The
q
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
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 (LTC 3727 Only)
V
OSENSE1, 2
= 0.5V (LTC3727 Only)
V
OSENSE1, 2
= 0.7V,V
SENSE1–, 2
–
= 12V
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
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
q
q
q
q
ELECTRICAL CHARACTERISTICS
CONDITIONS
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
q
MIN
TYP
3
670
20
MAX
UNITS
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
0.76
– 0.30
0.800
– 0.18
6.8
3.5
0.84
– 85
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
I
SCL1, 2
I
SDLHO
V
SENSE(MAX)
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
Phase Detector Output Current
Sinking Capability
Sourcing Capability
1.9
4.5
4
5
155
165
90
90
90
80
V
V
µA
µA
mV
mV
ns
ns
ns
ns
ns
ns
ns
V
RUN/SS1, 2
LT RUN/SS Pin Latchoff Arming Threshold V
RUN/SS1,
V
RUN/SS2
Rising from 3V (LTC3727 Only)
115
105
135
135
50
50
40
40
90
90
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
I
PLLFLTR
INTV
CC
Linear Regulator
7.2
7.5
0.2
70
6.9
7.3
0.3
V
PLLFLTR
= 1.2V
V
PLLFLTR
= 0V
V
PLLFLTR
≥
2.4V
350
220
460
380
255
530
50
f
PLLIN
< f
OSC
f
PLLIN
> f
OSC
–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
3727f
3
LTC3727/LTC3727-1
The
q
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 (LTC3727)
6V < V
IN
< 30V (LTC3727-1)
q
ELECTRICAL CHARACTERISTICS
3.3V Linear Regulator
MIN
3.25
TYP
3.35
0.5
0.05
0.05
MAX
3.45
2.5
0.2
0.3
UNITS
V
%
%
%
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC3727E/LTC3727E-1 are 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 3:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formulas:
LTC3727EG/LTC3727EG-1: T
J
= T
A
+ (P
D
• 95
°C/W)
LTC3727EUH-1: T
J
= T
A
+ (P
D
• 34
°C/W)
Note 4:
The LTC3727/LTC3727-1 are 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 PERFOR A CE CHARACTERISTICS
Efficiency vs Output Current
and Mode (Figure 13)
100
90
80
Burst Mode
OPERATION
FORCED
CONTINUOUS
MODE
100
V
IN
= 7V
90
90
EFFICIENCY (%)
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
3727 G01
80
EFFICIENCY (%)
70
CONSTANT
FREQUENCY
(BURST DISABLE)
4
U W
Efficiency vs Output Current
(Figure 13)
100
Efficiency vs Input Voltage
(Figure 13)
V
OUT
= 5V
I
OUT
= 3A
V
IN
= 10V
V
IN
= 15V
V
IN
= 20V
80
70
70
60
V
OUT
= 5V
0.1
0.01
1
OUTPUT CURRENT (A)
10
3727 G02
60
50
0.001
50
5
25
15
INPUT VOLTAGE (V)
35
3727 G03
3727f
LTC3727/LTC3727-1
TYPICAL PERFOR A CE CHARACTERISTICS
Supply Current vs Input Voltage
and Mode (Figure 13)
1000
160
140
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
3727 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
3727 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
3727 G10
NORMALIZED V
OUT
(%)
100
–0.2
V
ITH
(V)
U W
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
120
100
80
60
40
20
0
6.8
0
5
10
15
25
20
INPUT VOLTAGE (V)
30
35
3727 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 ON NOMINAL OUTPUT VOLTAGE (%)
3727 G08
0
1
2
3
4
V
RUN/SS
(V)
5
6
3727 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
3727 G11
0
1
2
3
V
RUN/SS
(V)
4
5
6
3727 G12
3727f
5
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