1
LTC3780
3780f
High Efficiency, Synchronous,
4-Switch Buck-Boost Controller
Single Inductor Architecture Allows V
IN
Above,
Below or Equal to V
OUT
Wide V
IN
Range: 4V to 36V Operation
Synchronous Rectification: Up to 98% Efficiency
Current Mode Control
1% Output Voltage Accuracy: 0.8V < V
OUT
< 30V
Phase-Lockable Fixed Frequency: 200kHz to 400kHz
Power Good Output Voltage Monitor
Internal LDO for MOSFET Supply
Quad N-Channel MOSFET Synchronous Drive
V
OUT
Disconnected from V
IN
During Shutdown
Adjustable Soft-Start Current Ramping
Foldback Output Current Limiting
Selectable Low Current Modes
Output Overvoltage Protection
Available in 24-Lead SSOP and Exposed Pad
(5mm 5mm) 32-Lead QFN Packages
Automotive Systems
Telecom Systems
DC Power Distribution Systems
High Power Battery-Operated Devices
Industrial Control
High Efficiency Buck-Boost Converter
DESCRIPTIO
U
FEATURES
APPLICATIO S
U
TYPICAL APPLICATIO
U
+
V
IN
TG2
0.1F
0.1F
BOOST2
SW2
BG2
TG1
BOOST1
SW1
BG1
PLLIN
RUN
V
OSENSE
I
TH
SS
SGND
FCB
0.010
4.7F
2200pF
1F
CER
100F
16V
CER
ON/OFF
0.1F
1000pF
2H
20k
PGOOD
LTC3780
INTV
CC
SENSE
+
SENSE
PGND
7.5k
3780 TA01
105k
1%
22F
50V
CER
V
IN
4V TO 36V
V
OUT
12V
5A
The LTC
3780 is a high performance buck-boost switch-
ing regulator controller that operates from input voltages
above, below or equal to the output voltage. The constant
frequency current mode architecture allows a phase-
lockable frequency of up to 400kHz. With a wide 4V to 30V
(36V maximum) input and output range and seamless
transfers between operating modes, the LTC3780 is ideal
for automotive, telecom and battery-powered systems.
The operating mode of the controller is determined through
the FCB pin. For boost operation, the FCB mode pin can
select among Burst Mode
operation, Discontinuous mode
and Forced Continuous mode. During buck operation, the
FCB mode pin can select among Skip-Cycle mode, Discon-
tinuous mode and Forced Continuous mode. Burst Mode
operation and Skip-Cycle mode provide high efficiency
operation at light loads while Forced Continuous mode
and Discontinuous mode operate at a constant frequency.
Fault protection is provided by an output overvoltage
comparator and internal foldback current limiting. A Power
Good output pin indicates when the output is within 7.5%
of its designed set point.
Efficiency and Power Loss
V
OUT
= 12V, I
LOAD
= 5A
V
IN
(V)
0
EFFICIENCY (%)
POWER LOSS (W)
90
95
100
15
25
3780 TA01b
85
80
5
10
20
30
35
75
70
8
9
10
7
6
5
4
3
2
1
0
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents, including 5481178, 6304066, 5929620, 5408150, 6580258,
patent pending on current mode architecture and protection
2
LTC3780
3780f
Input Supply Voltage (V
IN
)........................ 0.3V to 36V
Topside Driver Voltages
(BOOST1, BOOST2) .................................. 0.3V to 42V
Switch Voltage (SW1, SW2) ........................ 5V to 36V
INTV
CC
, EXTV
CC
, RUN, SS, (BOOST SW1),
(BOOST2 SW2), PGOOD .......................... 0.3V to 7V
PLLIN Voltage .......................................... 0.3V to 5.5V
PLLFLTR Voltage ...................................... 0.3V to 2.7V
FCB, STBYMD Voltages ....................... 0.3V to INTV
CC
I
TH
, V
OSENSE
Voltages .............................. 0.3V to 2.4V
ABSOLUTE
M
AXI
M
U
M
RATINGS
W
W
W
U
Peak Output Current <10ms (TG1, TG2, BG1, BG2) .. 3A
INTV
CC
Peak Output Current ................................ 40mA
Operating Temperature Range (Note 7)
LTC3780E ........................................... 40C to 85C
LTC3780I ............................................ 40C to 85C
Junction Temperature (Note 2) ............................ 125C
Storage Temperature Range .................. 65C to 125C
Lead Temperature (Soldering, 10 sec)
SSOP Only ........................................................ 300C
(Note 1)
ORDER PART
NUMBER
LTC3780EG
LTC3780IG
T
JMAX
= 125C,
JA
= 130C/W
PACKAGE/ORDER I
N
FOR
M
ATIO
N
W
U
U
Consult LTC Marketing for parts specified with wider operating temperature ranges.
1
2
3
4
5
6
7
8
9
10
11
12
TOP VIEW
G PACKAGE
24-LEAD PLASTIC SSOP
24
23
22
21
20
19
18
17
16
15
14
13
PGOOD
SS
SENSE
+
SENSE
I
TH
V
OSENSE
SGND
RUN
FCB
PLLFLTR
PLLIN
STBYMD
BOOST1
TG1
SW1
V
IN
EXTV
CC
INTV
CC
BG1
PGND
BG2
SW2
TG2
BOOST2
ORDER PART
NUMBER
LTC3780EUH
LTC3780IUH
32 31 30 29 28 27 26 25
9
10 11 12
TOP VIEW
33
UH PACKAGE
32-LEAD (5mm 5mm) PLASTIC QFN
13 14 15 16
17
18
19
20
21
22
23
24
8
7
6
5
4
3
2
1
SENSE
+
SENSE
I
TH
V
OSENSE
SGND
RUN
FCB
PLLFTR
SW1
V
IN
EXTV
CC
INTV
CC
BG1
PGND
BG2
SW2
NC
SS
PGOOD
NC
NC
BOOST1
TG1
NC
NC
PLLIN
STBYMD
NC
NC
BOOST2
TG2
NC
T
JMAX
= 125C,
JA
= 34C/W
EXPOSED PAD (PIN 33) IS SGND
(MUST BE SOLDERED TO PCB)
UH PART
MARKING
3780
3780I
The
indicates specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25C. V
IN
= 15V unless otherwise noted.
ELECTRICAL CHARACTERISTICS
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Main Control Loop
V
OSENSE
Feedback Reference Voltage
I
TH
= 1.2V (Note 3)
0.792
0.800
0.808
V
I
VOSENSE
Feedback Pin Input Current
(Note 3)
5
50
nA
V
LOADREG
Output Voltage Load Regulation
(Note 3)
I
TH
= 1.2V to 0.7V
0.1
0.5
%
I
TH
= 1.2V to 1.8V
0.1
0.5
%
3
LTC3780
3780f
V
REF(LINEREG)
Reference Voltage Line Regulation
V
IN
= 4V to 30V, I
TH
= 1.2V (Note 3)
0.002
0.02
%/V
g
m(EA)
Error Amplifier Transconductance
I
TH
= 1.2V, Sink/Source = 3A (Note 3)
0.32
mS
g
m(GBW)
Error Amplifier GBW
0.6
MHz
I
Q
Input DC Supply Current
(Note 4)
Normal
2400
A
Standby
V
RUN
= 0V, V
STBYMD
> 2V
1500
A
Shutdown Supply Current
V
RUN
= 0V, V
STBYMD
= Open
55
70
A
V
FCB
Forced Continuous Threshold
0.76
0.800
0.84
V
I
FCB
Forced Continuous Pin Current
V
FCB
= 0.85V
0.30
0.18
0.1
A
V
BINHIBIT
Burst Inhibit (Constant Frequency)
Measured at FCB Pin
5.3
5.5
V
Threshold
UVLO
Undervoltage Reset
V
IN
Falling
3.8
4
V
V
OVL
Feedback Overvoltage Lockout
Measured at V
OSENSE
Pin
0.84
0.86
0.88
V
I
SENSE
Sense Pins Total Source Current
V
SENSE
= V
SENSE
+
= 0V
380
A
V
STBYMD(START)
Start-Up Threshold
V
STBYMD
Rising
0.4
0.7
V
V
STBYMD(KA)
Keep-Alive Power-On Threshold
V
STBYMD
Rising, V
RUN
= 0V
1.25
V
DF MAX, BOOST Maximum Duty Factor
% Switch C On
99
%
DF MAX, BUCK
Maximum Duty Factor
% Switch A On (in Dropout)
99
%
V
RUN(ON)
RUN Pin On Threshold
V
RUN
Rising
1
1.5
2
V
I
SS
Soft-Start Charge Current
V
RUN
= 2V
0.5
1.2
A
V
SENSE(MAX)
Maximum Current Sense Threshold
Boost: V
OSENSE
= V
REF
50mV
160
185
mV
Buck: V
OSENSE
= V
REF
50mV
95
130
150
mV
V
SENSE(MIN,BUCK)
Minimum Current Sense Threshold
Discontinuous Mode
6
mV
TG1, TG2 t
r
TG Rise Time
C
LOAD
= 3300pF (Note 5)
50
ns
TG1, TG2 t
f
TG Fall Time
C
LOAD
= 3300pF (Note 5)
45
ns
BG1, BG2 t
r
BG Rise Time
C
LOAD
= 3300pF (Note 5)
45
ns
BG1, BG2 t
f
BG Fall Time
C
LOAD
= 3300pF (Note 5)
55
ns
TG1/BG1 t
1D
TG1 Off to BG1 On Delay,
C
LOAD
= 3300pF Each Driver
80
ns
Switch C On Delay
BG1/TG1 t
2D
BG1 Off to TG1 On Delay,
C
LOAD
= 3300pF Each Driver
80
ns
Synchronous Switch D On Delay
TG2/BG2 t
3D
TG2 Off to BG2 On Delay,
C
LOAD
= 3300pF Each Driver
80
ns
Synchronous Switch B On Delay
BG2/TG2 t
4D
BG2 Off to TG2 On Delay,
C
LOAD
= 3300pF Each Driver
80
ns
Switch A On Delay
Mode
BG1 Off to BG2 On Delay,
C
LOAD
= 3300pF Each Driver
90
ns
Transition 1
Switch A On Delay
Mode
BG2 Off to BG1 On Delay,
C
LOAD
= 3300pF Each Driver
90
ns
Transition 2
Synchronous Switch D On Delay
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
The
indicates specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25C. V
IN
= 15V unless otherwise noted.
ELECTRICAL CHARACTERISTICS
4
LTC3780
3780f
The
indicates specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25C. V
IN
= 15V unless otherwise noted.
ELECTRICAL CHARACTERISTICS
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: T
J
for the QFN package is calculated from the temperature T
A
and
power dissipation P
D
according to the following formula:
T
J
= T
A
+ (P
D
34C/W)
Note 3: The IC is tested in a feedback loop that servos V
ITH
to a specified
voltage and measures the resultant V
OSENSE
.
Note 4: Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency.
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 LTC3780E is guaranteed to meet performance specifications
from 0C to 85C. Performance over the 40C to 85C operating
temperature range is assured by design, characterization and correlation
with statistical process controls. The LTC3780I is guaranteed and tested
over the 40C to 85C operating temperature range.
t
ON(MIN,BOOST)
Minimum On-Time for Main Switch in
Switch C (Note 6)
200
240
ns
Boost Operation
t
ON(MIN,BUCK)
Minimum On-Time for Synchronous
Switch B (Note 6)
180
220
ns
Switch in Buck Operation
Internal V
CC
Regulator
V
INTVCC
Internal V
CC
Voltage
7V < V
IN
< 30V, V
EXTVCC
= 5V
5.7
6
6.3
V
V
LDO(LOADREG)
Internal V
CC
Load Regulation
I
CC
= 0mA to 20mA, V
EXTVCC
= 5V
0.2
2
%
V
EXTVCC
EXTV
CC
Switchover Voltage
I
CC
= 20mA, V
EXTVCC
Rising
5.4
5.7
V
V
EXTVCC(HYS)
EXTV
CC
Switchover Hysteresis
200
mV
V
EXTVCC
EXTV
CC
Switch Drop Voltage
I
CC
= 20mA, V
EXTVCC
= 6V
150
300
mV
Oscillator and Phase-Locked Loop
f
NOM
Nominal Frequency
V
PLLFLTR
= 1.2V
260
300
330
kHz
f
LOW
Lowest Frequency
V
PLLFLTR
= 0V
170
200
220
kHz
f
HIGH
Highest Frequency
V
PLLFLTR
= 2.4V
340
400
440
kHz
R
PLLIN
PLLIN Input Resistance
50
k
I
PLLLPF
Phase Detector Output Current
f
PLLIN
< f
OSC
15
A
f
PLLIN
> f
OSC
15
A
PGOOD Output
V
FBH
PGOOD Upper Threshold
V
OSENSE
Rising
5.5
7.5
10
%
V
FBL
PGOOD Lower Threshold
V
OSENSE
Falling
5.5
7.5
10
%
V
FB(HYST)
PGOOD Hysteresis
V
OSENSE
Returning
2.5
%
V
PGL
PGOOD Low Voltage
I
PGOOD
= 2mA
0.1
0.3
V
I
PGOOD
PGOOD Leakage Current
V
PGOOD
= 5V
1
A
5
LTC3780
3780f
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
Efficiency vs Output Current
(Boost Operation)
Efficiency vs Output Current
Efficiency vs Output Current
(Buck Operation)
Supply Current vs Input Voltage
Internal 6V LDO Line Regulation
EXTV
CC
Voltage Drop
INTV
CC
and EXTV
CC
Switch
Voltage vs Temperature
Load Regulation
I
LOAD
(A)
0.01
40
EFFICIENCY (%)
80
90
100
0.1
1
10
3780 G01
70
60
50
BURST
DCM
CCM
V
IN
= 6V
V
OUT
= 12V
I
LOAD
(A)
0.01
40
EFFICIENCY (%)
80
90
100
0.1
1
10
3780 G02
70
60
50
BURST
DCM
CCM
V
IN
= 12V
V
OUT
= 12V
I
LOAD
(A)
0.01
40
EFFICIENCY (%)
80
90
100
0.1
1
10
3780 G03
70
60
50
SC
DCM
CCM
V
IN
= 18V
V
OUT
= 12V
INPUT VOLTAGE (V)
0
5
0
SUPPLY CURRENT (
A)
1000
2500
10
20
25
3780 G04
500
2000
1500
15
30
35
V
FCB
= 0V
STANDBY
SHUTDOWN
INPUT VOLTAGE (V)
0
INTV
CC
VOLTAGE (V)
5.5
6.0
6.5
15
25
3780 G05
5.0
4.5
5
10
20
30
35
4.0
3.5
CURRENT (mA)
1
0
EXTV
CC
VOLTAGE DROP (mV)
20
40
60
80
100
120
10
20
30
40
3780 G06
50
TEMPERATURE (C)
50
5.55
INTV
CC
AND EXTV
CC
SWITCH VOLTAGE (V)
5.60
5.70
5.75
5.80
6.05
5.90
0
50
75
3780 G07
5.65
5.95
6.00
5.85
25
25
100
125
INTV
CC
VOLTAGE
EXTV
CC
SWITCHOVER THRESHOLD
EXTV
CC
Switch Resistance
vs Temperature
TEMPERATURE (C)
50
25
0
EXTV
CC
SWITCH RESISTANCE (
)
2
5
0
50
75
3780 G08
1
4
3
25
100
125
LOAD CURRENT (A)
0
NORMALIZED V
OUT
(%)
0.2
0.1
0
4
3780 G09
0.3
0.4
0.5
1
2
3
5
V
IN
= 18V
FCB = 0V
V
OUT
= 12V
V
IN
= 12V
V
IN
= 6V
T
A
= 25C unless otherwise noted.
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