FEATURES
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LTC3728L-1
Dual, 550kHz, 2-Phase
Synchronous Regulator
DESCRIPTION
The LTC
®
3728L-1 is a dual high performance 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 LTC3728L-1
is identical to the LTC3728L except that the LTC3728L-1
lacks the over current latchoff feature.
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 microproces-
sor generations, and a wide 4.5V to 28V (30V maximum/
35V for LTC3728LI-1) input supply range encompasses
all battery chemistries.
A RUN/SS pin for each controller provides soft-start.
Current foldback limits MOSFET dissipation during short-
circuit conditions. The FCB mode pin can select among
Burst Mode operation, constant frequency mode and
continuous inductor current mode or regulate a secondary
winding. The LTC3728L-1 includes a power good output
pin that indicates when both outputs are within 7.5% of
their designed set point.
L,
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 5929620, 6177787, 6144199, 5471178, 5994885, 6100678.
Dual, 180° Phased 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 Indicator
Phase-Lockable Fixed Frequency 250kHz to 550kHz
Over Current Latchoff Disabled
Wide V
IN
Range: 4.5V to 28V (35V for LTC3728LI-1)
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
5V and 3.3V Standby Regulators
3 Selectable Operating Modes: Constant Frequency,
Burst Mode
®
Operation and PWM
5mm
×
5mm QFN and 28-Lead Narrow SSOP
Packages
APPLICATIONS
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Notebook and Palmtop Computers
Telecom Systems
Portable Instruments
Battery-Operated Digital Devices
DC Power Distribution Systems
TYPICAL APPLICATION
+
4.7μF
M1
L1
3.2μH
D3
V
IN
PGOOD INTV
CC
TG1
TG2
C
B1
, 0.1μF
BOOST1
SW1
BG1
f
IN
500kHz
PLLIN
SENSE1
+
R
SENSE1
0.01Ω
V
OUT1
5V
5A
1000pF
SENSE1
–
V
OSENSE1
I
TH1
C
SS1
0.1μF
SENSE2
–
V
OSENSE2
I
TH2
C
SS2
0.1μF
LTC3728L-1
BOOST2
SW2
BG2
PGND
SENSE2
+
1000pF
D4
1μF
CERAMIC
M2
V
IN
5.2V TO 28V
C
IN
22μF
50V
CERAMIC
L2
3.2μH
C
B2
, 0.1μF
R
SENSE2
0.01Ω
V
OUT2
3.3V
5A
+
R2
105k
C
OUT1
1%
47μF
6V
SP
M1, M2: FDS6982S
R1
20k
1%
C
C1
220pF
R
C1
15k
RUN/SS1 SGND RUN/SS2
C
C2
220pF
R
C2
15k
R3
20k
1%
R4
63.4k
1%
C
OUT
56μF
6V
SP
+
3728l1 F01
Figure 1. High Efficiency Dual 5V/3.3V Step-Down Converter
3728l1fc
1
LTC3728L-1
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Input Supply Voltage (V
IN
) .........................30V to – 0.3V
Input Supply Voltage (V
IN
) LTC3728LI-1 ....35V to – 0.3V
Top Side Driver Voltages
(BOOST1, BOOST2) ............................... 36V to –0.3V
(BOOST1, BOOST2) LTC3728LI-1 .......... 38V to –0.3V
Switch Voltage (SW1, SW2) ........................... 30V to –5V
Switch Voltage (SW1, SW2) LTC3728LI-1... 35V to –0.3V
INTV
CC,
EXTV
CC
, RUN/SS1, RUN/SS2, (BOOST1-SW1),
(BOOST2-SW2), PGOOD ......................... 7V to –0.3V
INTV
CC,
EXTV
CC
LTC3728LI-1 ....................... 8V to –0.3V
SENSE1
+
, SENSE2
+
, SENSE1
–
,
SENSE2
–
Voltages .....................(1.1)INTV
CC
to –0.3V
PLLIN, PLLFLTR, 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 7).... –40°C to 85°C
Junction Temperature (Note 2) ............................. 125°C
Storage Temperature Range................... –65°C to 125°C
Reflow Peak Body Temperature (UH Package) ...... 260°C
Lead Temperature (Soldering, 10 sec)
GN Package ...................................................... 300°C
PIN CONFIGURATION
TOP VIEW
SENSE1
–
RUN/SS1
SENSE1
+
SENSE
–
V
OSENSE1
PLLFLTR
PLLIN
FCB
I
TH1
SGND
1
2
3
4
5
6
7
8
9
28 PGOOD
NC
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
1
PLLFLTR 2
PLLIN 3
FCB 4
I
TH1
5
SGND 6
3.3V
OUT
7
I
TH2
8
9 10 11 12 13 14 15 16
RUN/SS2
SW2
TG2
V
OSENSE2
NC
SENSE2
–
SENSE2
+
NC
33
TOP VIEW
RUN/SS1
SENSE1
+
PGOOD
SW1
24 BOOST1
23 V
IN
22 BG1
21 EXTV
CC
20 INTV
CC
19 PGND
18 BG2
17 BOOST2
TG1
NC
32 31 30 29 28 27 26 25
3.3V
OUT
10
I
TH2
11
V
OSENSE2
12
SENSE2
–
13
SENSE2
+
14
GN PACKAGE
28-LEAD NARROW PLASTIC SSOP
UH PACKAGE
32-LEAD (5mm 5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 95°C/W
T
JMAX
= 125°C,
θ
JA
= 34°C/W
EXPOSED PAD (PIN 33) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING
LTC3728LEGN-1#PBF
LTC3728LEGN-1#TRPBF LTC3728LEGN-1
LTC3728LIGN-1#PBF
LTC3728LIGN-1#TRPBF
LTC3728LIGN-1
LTC3728LEUH-1#PBF
LTC3728LEUH-1#TRPBF 728LE1
LTC3728LIUH-1#PBF
LTC3728LIUH-1#TRPBF
3728L1
LEAD BASED FINISH
TAPE AND REEL
PART MARKING
LTC3728LEGN-1
LTC3728LEGN-1#TR
LTC3728LEGN-1
LTC3728LIGN-1
LTC3728LIGN-1#TR
LTC3728LIGN-1
LTC3728LEUH-1
LTC3728LEUH-1#TR
728LE1
LTC3728LIUH-1
LTC3728LIUH-1#TR
3728L1
Consult LTC Marketing for parts specified with wider operating temperature ranges.
PACKAGE DESCRIPTION
28-Lead Narrow Plastic SSOP
28-Lead Narrow Plastic SSOP
32-Lead (5mm
×
5mm) Plastic DFN
32-Lead (5mm
×
5mm) Plastic DFN
PACKAGE DESCRIPTION
28-Lead Narrow Plastic SSOP
28-Lead Narrow Plastic SSOP
32-Lead (5mm
×
5mm) Plastic DFN
32-Lead (5mm
×
5mm) Plastic DFN
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 85°C
–40°C to 85°C
–40°C to 85°C
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 85°C
–40°C to 85°C
–40°C to 85°C
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/
3728l1fc
2
LTC3728L-1
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
(Note 3); I
TH1, 2
Voltage = 1.2V
(Note 3)
V
IN
= 3.6V to 30V (Note 3)
(Note 3)
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 3)
I
TH1, 2
= 1.2V; (Note 3)
(Note 4)
V
IN
= 15V; EXTV
CC
Tied to V
OUT1
; V
OUT1
= 5V
V
RUN/SS1, 2
= 0V
●
●
●
●
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
0.788
TYP
0.800
–5
0.002
0.1
– 0.1
1.3
3
450
20
0.76
– 0.50
0.800
–0.18
4.3
●
●
MAX
0.812
–50
0.02
0.5
–0.5
UNITS
V
nA
%/V
%
%
mmho
MHz
μA
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
35
0.84
–0.1
4.8
4
0.88
V
FCB
I
FCB
V
BINHIBIT
UVLO
V
OVL
I
SENSE
DF
MAX
I
RUN/SS1, 2
V
SENSE(MAX)
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–
= 5V
V
OSENSE1, 2
= 0.7V,V
SENSE1–, 2–
= 5V
(Note 5)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
(Note 5)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
C
LOAD
= 3300pF Each Driver
C
LOAD
= 3300pF Each Driver
Tested with a Square Wave (Note 6)
6V < V
IN
< 30V, V
EXTVCC
= 4V
I
CC
= 0 to 20mA, V
EXTVCC
= 4V
I
CC
= 20mA, V
EXTVCC
= 5V
I
CC
= 20mA, EXTV
CC
Ramping Positive
●
●
3.5
0.84
–90
98
0.5
1.0
65
62
0.86
–60
99.4
1.2
1.5
75
75
55
55
45
45
80
80
100
4.8
5.0
0.2
100
4.5
4.7
0.2
V
RUN/SS1, 2
ON RUN/SS Pin ON Threshold
2.0
85
88
100
100
100
90
V
mV
mV
ns
ns
ns
ns
ns
ns
ns
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
INTV
CC
Linear Regulator
5.2
2.0
200
V
%
mV
V
V
440
290
590
kHz
kHz
kHz
kΩ
3728l1fc
Oscillator and Phase-Locked Loop
V
PLLFLTR
= 1.2V
V
PLLFLTR
= 0V
V
PLLFLTR
≥ 2.4V
360
230
480
400
260
550
50
3
LTC3728L-1
ELECTRICAL CHARACTERISTICS
SYMBOL
I
PLLFLTR
PARAMETER
Phase Detector Output Current
Sinking Capability
Sourcing Capability
3.3V Regulator Output Voltage
3.3V Regulator Load Regulation
3.3V Regulator Line Regulation
Leakage Current in Shutdown
PGOOD Voltage Low
PGOOD Leakage Current
PGOOD Trip Level, Either Controller
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
f
PLLIN
< f
OSC
f
PLLIN
> f
OSC
No Load
I
3.3
= 0 to 10mA
6V < V
IN
< 30V
V
RUN/SS1
= 0V; V
RUN/SS2
= 0V, V
IN
= 3V
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
●
●
MIN
TYP
–15
15
MAX
UNITS
μA
μA
3.3V Linear Regulator
V
3.3OUT
V
3.3IL
V
3.3VL
I
3.3LEAK
PGOOD Output
V
PGL
I
PGOOD
V
PG
0.1
0.3
±1
– 9.5
9.5
V
μA
%
%
3.2
3.35
0.5
0.05
10
3.45
2
0.2
50
V
%
%
μA
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:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formulas:
LTC3728LUH-1: T
J
= T
A
+ (P
D
• 34°C/W)
LTC3728LGN-1: T
J
= T
A
+ (P
D
• 95°C/W)
Note 3:
The IC is tested in a feedback loop that servos V
ITH1, 2
to a
specified voltage and measures the resultant V
OSENSE1, 2.
Note 4:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Applications Information.
Note 5:
Rise and fall times are measured using 10% and 90% levels. Delay
times are measured using 50% levels.
Note 6:
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).
Note 7:
The LTC3728LE-1 are 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 LTC3728LI-1 is
guaranteed to meet performance specifications over the full –40°C to 85°C
operating temperature range
TYPICAL PERFORMANCCE CHARACTERISTICS
Efficiency vs Output Current
and Mode (Figure 13)
100
90
80
EFFICIENCY (%)
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.001
0.1
0.01
1
OUTPUT CURRENT (A)
FORCED
CONTINUOUS
MODE (PWM)
CONSTANT
FREQUENCY
(BURST DISABLE)
V
IN
= 15V
V
OUT
= 5V
f = 250kHz
10
3728L1 G01
Efficiency vs Output Current
(Figure 13)
100
V
IN
= 7V
90
EFFICIENCY (%)
V
IN
= 10V
V
IN
= 15V
V
IN
= 20V
70
90
100
Efficiency vs Input Voltage
(Figure 13)
Burst Mode
OPERATION
80
80
70
60
V
OUT
= 5V
f = 250kHz
50
0.001
60
50
0.1
0.01
1
OUTPUT CURRENT (A)
10
3728L1 G02
V
OUT
= 5V
I
OUT
= 3A
f = 250kHz
5
25
15
INPUT VOLTAGE (V)
35
3728L1 G03
3728l1fc
4
LTC3728L-1
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
800
SUPPLY CURRENT (μA)
EXTV
CC
VOLTAGE DROP (mV)
150
600
BOTH
CONTROLLERS ON
400
100
50
200
SHUTDOWN
0
0
5
20
15
10
INPUT VOLTAGE (V)
25
30
EXTV
CC
SWITCHOVER THRESHOLD
0
0
10
20
CURRENT (mA)
30
40
3728L1 G05
4.70
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
3728L1 G04
3728L1 G06
Internal 5V LDO Line Regulation
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
0
V
SENSE
(mV)
I
LOAD
= 1mA
75
Maximum Current Sense Threshold
vs Duty Factor
80
70
60
V
SENSE
(mV)
0
20
40
60
DUTY FACTOR (%)
80
100
3728L1 G08
Maximum Current Sense Threshold
vs Percent of Nominal Output
Voltage (Foldback)
50
50
40
30
20
10
0
50
0
100
25
75
PERCENT ON NOMINAL OUTPUT VOLTAGE (%)
3728L1 G09
25
3728L1 G07
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)
70
60
50
40
30
20
10
0
64
–10
–20
–30
0
1
3
4
2
COMMON MODE VOLTAGE (V)
5
3728L1 G11
Current Sense Threshold
vs I
TH
Voltage
60
V
SENSE
(mV)
72
40
68
20
0
0
1
2
3
V
RUN/SS
(V)
3728L1 G10
4
5
6
60
0
0.5
1
1.5
V
ITH
(V)
2
2.5
3728L1 G12
3728l1fc
5
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