1
LTC3727/LTC3727-1
3727f
High Efficiency, 2-Phase
Synchronous Step-Down Switching Regulators
Figure 1. High Efficiency Dual 12V/5V Step-Down Converter
s
Wide Output Voltage Range: 0.8V
V
OUT
14V
s
Out-of-Phase Controllers Reduce Required Input
Capacitance and Power Supply Induced Noise
s
OPTI-LOOP
Compensation Minimizes C
OUT
s
1% Output Voltage Accuracy
s
Power Good Output Voltage Monitor
s
Phase-Lockable Fixed Frequency 250kHz to 550kHz
s
Latched Short-Circuit Shutdown (LTC3727 Only)
s
Dual N-Channel MOSFET Synchronous Drive
s
Wide V
IN
Range: 4V to 36V Operation
s
Very Low Dropout Operation: 99% Duty Cycle
s
Adjustable Soft-Start Current Ramping
s
Foldback Output Current Limiting
s
Output Overvoltage Protection
s
Low Shutdown I
Q
: 20
A
s
Small 28-Lead SSOP Package
s
LTC3727-1 Also Available in the 5mm
5mm QFN
Package
s
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.
s
Telecom Systems
s
Automotive Systems
s
Battery-Operated Digital Devices
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode and OPTI-LOOP are registered trademarks of Linear Technology Corporation.
+
4.7
F
M2
M1
0.1
F
105k
1%
1000pF
8
H
220pF
1
F
CERAMIC
22
F
50V
CERAMIC
+
47
F
6V
SP
0.015
20k
1%
15k
V
OUT1
5V
5A
M4
M3
0.1
F
280k
1%
15
H
220pF
1000pF
+
56
F
15V
SP
0.015
20k
1%
15k
V
OUT2
12V
4A
TG1
TG2
BOOST1
BOOST2
SW1
SW2
BG1
BG2
SGND
PGND
SENSE1
+
SENSE2
+
SENSE1
SENSE2
V
OSENSE1
V
OSENSE2
I
TH1
I
TH2
V
IN
PGOOD INTV
CC
RUN/SS1
RUN/SS2
V
IN
18V TO 28V
M1, M2, M3, M4: FDS6680A
1628 F01
0.1
F
0.1
F
LTC3727/
LTC3727-1
PLLIN
DESCRIPTIO
U
FEATURES
APPLICATIO S
U
TYPICAL APPLICATIO
U
2
LTC3727/LTC3727-1
3727f
ORDER PART
NUMBER
LTC3727EG
LTC3727EG-1
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
T
JMAX
= 125
C,
JA
= 95
C/W
ABSOLUTE AXI U RATI GS
W
W
W
U
PACKAGE/ORDER I FOR ATIO
U
U
W
1
2
3
4
5
6
7
8
9
10
11
12
13
14
TOP VIEW
G PACKAGE
28-LEAD PLASTIC SSOP
28
27
26
25
24
23
22
21
20
19
18
17
16
15
RUN/SS1
SENSE1
+
SENSE1
V
OSENSE1
PLLFLTR
PLLIN
FCB
I
TH1
SGND
3.3V
OUT
I
TH2
V
OSENSE2
SENSE2
SENSE2
+
PGOOD
TG1
SW1
BOOST1
V
IN
BG1
EXTV
CC
INTV
CC
PGND
BG2
BOOST2
SW2
TG2
RUN/SS2
Consult LTC Marketing for parts specified with wider operating temperature ranges.
(Note 1)
I
TH1,
I
TH2
, V
OSENSE1
, V
OSENSE2
Voltages ... 2.7V to 0.3V
Peak Output Current <10
s (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
32 31 30 29 28 27 26 25
9
10 11 12 13
TOP VIEW
14 15 16
17
18
19
20
21
22
23
24
8
7
6
5
4
3
2
1
V
OSENSE1
PLLFLTR
PLLIN
FCB
I
TH1
SGND
3.3V
OUT
I
TH2
BOOST1
V
IN
BG1
EXTV
CC
INTV
CC
PGND
BG2
BOOST2
NC
SENSE1
SENSE1
+
NC
RUN/SS1
PGOOD
TG1
SW1
V
OSENSE2
NC
SENSE2
SENSE2
+
RUN/SS2
TG2
SW2
NC
UH PACKAGE
32-LEAD (5mm
5mm) PLASTIC QFN
ORDER PART
NUMBER
LTC3727EUH-1
T
JMAX
= 125
C,
JA
= 34
C/W
EXPOSED PAD IS SGND
(MUST BE SOLDERED TO PCB)
UH PART
MARKING
37271
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.
ELECTRICAL CHARACTERISTICS
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Main Control Loops
V
OSENSE1, 2
Regulated Feedback Voltage
(Note 4); I
TH1, 2
Voltage = 1.2V
q
0.792
0.800
0.808
V
I
VOSENSE1, 2
Feedback Current
(Note 4)
5
50
nA
V
REFLNREG
Reference Voltage Line Regulation
V
IN
= 3.6V to 30V (Note 4)
0.002
0.02
%/V
V
LOADREG
Output Voltage Load Regulation
(Note 4)
Measured in Servo Loop;
I
TH
Voltage = 1.2V to 0.7V
q
0.1
0.5
%
Measured in Servo Loop;
I
TH
Voltage = 1.2V to 2.0V
q
0.1
0.5
%
g
m1, 2
Transconductance Amplifier g
m
I
TH1, 2
= 1.2V; Sink/Source 5
A (Note 4)
1.3
mmho
3
LTC3727/LTC3727-1
3727f
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.
ELECTRICAL CHARACTERISTICS
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
g
mGBW1, 2
Transconductance Amplifier GBW
I
TH1, 2
= 1.2V (Note 4)
3
MHz
I
Q
Input DC Supply Current
(Note 5)
Normal Mode
V
IN
= 15V, EXTV
CC
Tied to V
OUT1
, V
OUT1
= 8.5V
670
A
Shutdown
V
RUN/SS1, 2
= 0V
20
35
A
V
FCB
Forced Continuous Threshold
q
0.76
0.800
0.84
V
I
FCB
Forced Continuous Pin Current
V
FCB
= 0.85V
0.30
0.18
0.05
A
V
BINHIBIT
Burst Inhibit (Constant Frequency)
Measured at FCB pin
6.8
7.3
V
Threshold
UVLO
Undervoltage Lockout
V
IN
Ramping Down
q
3.5
4
V
V
OVL
Feedback Overvoltage Lockout
Measured at V
OSENSE1, 2
q
0.84
0.86
0.88
V
I
SENSE
Sense Pins Total Source Current
(Each Channel) V
SENSE1
, 2
= V
SENSE1
+
, 2
+
= 0V
85
60
A
DF
MAX
Maximum Duty Factor
In Dropout
98
99.4
%
I
RUN/SS1, 2
Soft-Start Charge Current
V
RUN/SS1, 2
= 1.9V
0.5
1.2
A
V
RUN/SS1, 2
ON RUN/SS Pin ON Threshold
V
RUN/SS1,
V
RUN/SS2
Rising
1.0
1.5
1.9
V
V
RUN/SS1, 2
LT RUN/SS Pin Latchoff Arming Threshold V
RUN/SS1,
V
RUN/SS2
Rising from 3V (LTC3727 Only)
4.1
4.5
V
I
SCL1, 2
RUN/SS Discharge Current
Soft-Short Condition V
OSENSE1, 2
= 0.5V,
0.5
2
4
A
V
RUN/SS1, 2
= 4.5V (LTC 3727 Only)
I
SDLHO
Shutdown Latch Disable Current
V
OSENSE1, 2
= 0.5V (LTC3727 Only)
1.6
5
A
V
SENSE(MAX)
Maximum Current Sense Threshold
V
OSENSE1, 2
= 0.7V,V
SENSE1, 2
= 12V
115
135
155
mV
V
OSENSE1, 2
= 0.7V,V
SENSE1, 2
= 12V
q
105
135
165
mV
TG Transition Time:
(Note 6)
TG1, 2 t
r
Rise Time
C
LOAD
= 3300pF
50
90
ns
TG1, 2 t
f
Fall Time
C
LOAD
= 3300pF
50
90
ns
BG Transition Time:
(Note 6)
BG1, 2 t
r
Rise Time
C
LOAD
= 3300pF
40
90
ns
BG1, 2 t
f
Fall Time
C
LOAD
= 3300pF
40
80
ns
TG/BG t
1D
Top Gate Off to Bottom Gate On Delay
C
LOAD
= 3300pF Each Driver
90
ns
Synchronous Switch-On Delay Time
BG/TG t
2D
Bottom Gate Off to Top Gate On Delay
C
LOAD
= 3300pF Each Driver
90
ns
Top Switch-On Delay Time
t
ON(MIN)
Minimum On-Time
Tested with a Square Wave (Note 7)
180
ns
INTV
CC
Linear Regulator
V
INTVCC
Internal V
CC
Voltage
8.5V < V
IN
< 30V, V
EXTVCC
= 6V
7.2
7.5
7.8
V
V
LDO
INT
INTV
CC
Load Regulation
I
CC
= 0mA to 20mA, V
EXTVCC
= 6V
0.2
1.0
%
V
LDO
EXT
EXTV
CC
Voltage Drop
I
CC
= 20mA, V
EXTVCC
= 8.5V
70
160
mV
V
EXTVCC
EXTV
CC
Switchover Voltage
I
CC
= 20mA, EXTV
CC
Ramping Positive
q
6.9
7.3
V
V
LDOHYS
EXTV
CC
Hysteresis
0.3
V
Oscillator and Phase-Locked Loop
f
NOM
Nominal Frequency
V
PLLFLTR
= 1.2V
350
380
430
kHz
f
LOW
Lowest Frequency
V
PLLFLTR
= 0V
220
255
290
kHz
f
HIGH
Highest Frequency
V
PLLFLTR
2.4V
460
530
580
kHz
R
PLLIN
PLLIN Input Resistance
50
k
I
PLLFLTR
Phase Detector Output Current
Sinking Capability
f
PLLIN
< f
OSC
15
A
Sourcing Capability
f
PLLIN
> f
OSC
15
A
4
LTC3727/LTC3727-1
3727f
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)
Efficiency vs Output Current
and Mode (Figure 13)
Efficiency vs Output Current
(Figure 13)
Efficiency vs Input Voltage
(Figure 13)
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
OUTPUT CURRENT (A)
0.001
0
EFFICIENCY (%)
10
30
40
50
100
70
0.01
0.1
1
3727 G01
20
80
90
60
10
FORCED
CONTINUOUS
MODE
Burst Mode
OPERATION
V
IN
= 15V
V
OUT
= 8.5V
CONSTANT
FREQUENCY
(BURST DISABLE)
OUTPUT CURRENT (A)
0.001
EFFICIENCY (%)
70
80
10
3727 G02
60
50
0.01
0.1
1
100
90
V
IN
= 10V
V
IN
= 15V
V
IN
= 7V
V
IN
= 20V
V
OUT
= 5V
INPUT VOLTAGE (V)
5
EFFICIENCY (%)
70
80
3727 G03
60
50
15
25
35
100
V
OUT
= 5V
I
OUT
= 3A
90
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.
ELECTRICAL CHARACTERISTICS
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
3.3V Linear Regulator
V
3.3OUT
3.3V Regulator Output Voltage
No Load
q
3.25
3.35
3.45
V
V
3.3IL
3.3V Regulator Load Regulation
I
3.3
= 0mA to 10mA
0.5
2.5
%
V
3.3VL
3.3V Regulator Line Regulation
6V < V
IN
< 30V (LTC3727)
0.05
0.2
%
6V < V
IN
< 30V (LTC3727-1)
0.05
0.3
%
PGOOD Output
V
PGL
PGOOD Voltage Low
I
PGOOD
= 2mA
0.1
0.3
V
I
PGOOD
PGOOD Leakage Current
V
PGOOD
= 5V
1
A
V
PG
PGOOD Trip Level, Either Controller
V
OSENSE
with Respect to Set Output Voltage
V
OSENSE
Ramping Negative
6
7.5
9.5
%
V
OSENSE
Ramping Positive
6
7.5
9.5
%
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).
5
LTC3727/LTC3727-1
3727f
Maximum Current Sense Threshold
vs Duty Factor
Maximum Current Sense Threshold
vs Percent of Nominal Output
Voltage (Foldback)
Maximum Current Sense Threshold
vs V
RUN/SS
(Soft-Start)
Current Sense Threshold
vs I
TH
Voltage
Load Regulation
V
ITH
vs V
RUN/SS
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
DUTY FACTOR (%)
0
0
V
SENSE
(mV)
25
50
75
100
125
150
20
40
60
80
3727 G07
100
PERCENT ON NOMINAL OUTPUT VOLTAGE (%)
0
V
SENSE
(mV)
90
120
150
80
3727 G08
60
30
75
105
135
45
15
0
20
40
60
100
V
RUN/SS
(V)
0
50
V
SENSE
(mV)
75
100
125
150
1
2
3
4
3727 G09
5
6
V
SENSE(CM)
= 1.6V
V
ITH
(V)
0
V
SENSE
(mV)
25
50
75
1.5
2.5
3727 G10
0
25
50
0.5
1.0
2.0
100
125
150
LOAD CURRENT (A)
0
NORMALIZED V
OUT
(%)
0.2
0.1
4
3727 G11
0.3
0.4
1
2
3
5
0.0
FCB = 0V
V
IN
= 15V
FIGURE 1
V
RUN/SS
(V)
0
0
V
ITH
(V)
0.5
1.0
1.5
2.0
2.5
1
2
3
4
3727 G12
5
6
V
OSENSE
= 0.7V
Supply Current vs Input Voltage
and Mode (Figure 13)
EXTV
CC
Voltage Drop
INPUT VOLTAGE (V)
0
0
SUPPLY CURRENT (
A)
400
1000
10
20
3727 G04
200
800
600
30
BOTH
CONTROLLERS ON
SHUTDOWN
CURRENT (mA)
0
EXTV
CC
VOLTAGE DROP (mV)
60
80
100
30
50
3727 G05
40
20
0
10
20
40
120
140
160
V
EXTVCC
= 8.5V
Internal 7.5V LDO Line Regulation
INPUT VOLTAGE (V)
0
6.8
INTV
CC
VOLTAGE (V)
6.9
7.1
7.2
7.3
20
7.7
3727 G06
7.0
10
5
25
30
15
35
7.4
7.5
7.6
I
LOAD
= 1mA
PDF 
ZIP