LTC3780
High Efficiency, Synchronous,
4-Switch Buck-Boost Controller
FEATURES
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DESCRIPTION
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.
All registered trademarks and 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.
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
APPLICATIONS
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Automotive Systems
Telecom Systems
DC Power Distribution Systems
High Power Battery-Operated Devices
Industrial Control
TYPICAL APPLICATION
High Efficiency Buck-Boost Converter
V
IN
5V TO 32V
22µF
50V
CER
+
A
0.1µF
B
4.7µF
V
IN
PGOOD INTV
CC
TG2
BOOST2
SW2
BG2
2200pF
I
TH
0.1µF
SS
LTC3780
TG1
BOOST1
SW1
BG1
PLLIN
RUN
V
OSENSE
7.5k
1%
ON/OFF
0.1µF
1µF
CER
D
100µF
16V
CER
+
330µF
16V
V
OUT
12V
5A
100
95
EFFICIENCY (%)
Efficiency and Power Loss
V
OUT
= 12V, I
LOAD
= 5A
10
9
8
7
6
85
80
75
70
5
4
3
2
1
0
5
10
20
15
V
IN
(V)
25
30
35
0
POWER LOSS (W)
C
90
20k
105k
1%
SGND
FCB
SENSE
+
SENSE
–
PGND
0.010
3780 TA01b
4.7µH
3780 TA01
Rev G
Document Feedback
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1
LTC3780
ABSOLUTE MAXIMUM RATINGS
(Note 1)
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
, (BOOST – SW1),
(BOOST2 – SW2), PGOOD .......................... –0.3V to 7V
RUN, SS ....................................................... –0.3V to 6V
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
Peak Output Current <10µs (TG1, TG2, BG1, BG2) ......3A
INTV
CC
Peak Output Current ................................. 40mA
Operating Junction Temperature Range (Notes 2, 7)
LTC3780E ............................................–40°C to 85°C
LTC3780I ........................................... –40°C to 125°C
LTC3780MP ....................................... –55°C to 125°C
Storage Temperature Range .................. –65°C to 125°C
Lead Temperature (Soldering, 10 sec)
SSOP Only ........................................................ 300°C
PIN CONFIGURATION
TOP VIEW
BOOST1
PGOOD
TOP VIEW
PGOOD
SS
SENSE
+
SENSE
–
I
TH
V
OSENSE
SGND
RUN
FCB
1
2
3
4
5
6
7
8
9
24 BOOST1
23 TG1
22 SW1
21 V
IN
20 EXTV
CC
19 INTV
CC
18 BG1
17 PGND
16 BG2
15 SW2
14 TG2
13 BOOST2
SENSE
+
1
SENSE
–
2
I
TH
3
V
OSENSE
4
SGND 5
RUN 6
FCB 7
PLLFTR 8
9 10 11 12 13 14 15 16
NC
PLLIN
STBYMD
NC
NC
BOOST2
TG2
NC
33
NC
SS
TG1
NC
NC
NC
24 SW1
23 V
IN
22 EXTV
CC
21 INTV
CC
20 BG1
19 PGND
18 BG2
17 SW2
32 31 30 29 28 27 26 25
PLLFLTR 10
PLLIN 11
STBYMD 12
G PACKAGE
24-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 130°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
Rev G
2
For more information
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LTC3780
ORDER INFORMATION
LEAD FREE FINISH
LTC3780EG#PBF
LTC3780IG#PBF
LTC3780MPG#PBF
LTC3780EUH#PBF
LTC3780IUH#PBF
LEAD BASED FINISH
LTC3780EG
LTC3780IG
LTC3780MPG
LTC3780EUH
LTC3780IUH
TAPE AND REEL
LTC3780EG#TRPBF
LTC3780IG#TRPBF
LTC3780MPG#TRPBF
LTC3780EUH#TRPBF
LTC3780IUH#TRPBF
TAPE AND REEL
LTC3780EG#TR
LTC3780IG#TR
LTC3780MPG#TR
LTC3780EUH#TR
LTC3780IUH#TR
PART MARKING
LTC3780EG
LTC3780IG
LTC3780MPG
3780
3780I
PART MARKING
LTC3780EG
LTC3780IG
LTC3780MPG
3780
3780I
PACKAGE DESCRIPTION
24-Lead Plastic SSOP
24-Lead Plastic SSOP
24-Lead Plastic SSOP
32-Lead (5mm
×
5mm) Plastic QFN
32-Lead (5mm
×
5mm) Plastic QFN
PACKAGE DESCRIPTION
24-Lead Plastic SSOP
24-Lead Plastic SSOP
24-Lead Plastic SSOP
32-Lead (5mm
×
5mm) Plastic QFN
32-Lead (5mm
×
5mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 125°C
–55°C to 125°C
–40°C to 85°C
–40°C to 125°C
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 125°C
–55°C to 125°C
–40°C to 85°C
–40°C to 125°C
Contact the factory for parts specified with wider operating temperature ranges.
Tape and reel specifications.
Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix.
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
A
= 25°C. (Note 7) V
IN
= 15V unless otherwise noted.
SYMBOL
Main Control Loop
V
OSENSE
I
VOSENSE
V
LOADREG
V
REF(LINEREG)
g
m(EA)
g
m(GBW)
I
Q
Feedback Reference Voltage
Feedback Pin Input Current
Output Voltage Load Regulation
I
TH
= 1.2V, –40°C ≤ T ≤ 85°C (Note 3)
–55°C ≤ T ≤ 125°C
(Note 3)
(Note 3)
∆I
TH
= 1.2V to 0.7V
∆I
TH
= 1.2V to 1.8V
V
IN
= 4V to 30V, I
TH
= 1.2V (Note 3)
I
TH
= 1.2V, Sink/Source = 3µA (Note 3)
(Note 8)
(Note 4)
V
RUN
= 0V, V
STBYMD
> 2V
V
RUN
= 0V, V
STBYMD
= Open
0.76
V
FCB
= 0.85V
Measured at FCB Pin
V
IN
Falling
Measured at V
OSENSE
Pin
V
SENSE–
= V
SENSE+
= 0V
V
STBYMD
Rising
V
STBYMD
Rising, V
RUN
= 0V
0.4
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l
l
l
l
ELECTRICAL CHARACTERISTICS
PARAMETER
CONDITIONS
MIN
0.792
0.792
TYP
0.800
0.800
–5
0.1
–0.1
0.002
0.32
0.6
2400
1500
55
0.800
–0.18
5.3
3.8
MAX
0.808
0.811
–50
0.5
–0.5
0.02
UNITS
V
V
nA
%
%
%/V
mS
MHz
µA
µA
µA
V
µA
V
V
V
µA
V
V
Reference Voltage Line Regulation
Error Amplifier Transconductance
Error Amplifier GBW
Input DC Supply Current
Normal
Standby
Shutdown Supply Current
Forced Continuous Threshold
Forced Continuous Pin Current
Burst Inhibit (Constant Frequency)
Threshold
Undervoltage Reset
Feedback Overvoltage Lockout
Sense Pins Total Source Current
Start-Up Threshold
Keep-Alive Power-On Threshold
70
0.84
–0.1
5.5
4
0.88
V
FCB
I
FCB
V
BINHIBIT
UVLO
V
OVL
I
SENSE
V
STBYMD(START)
V
STBYMD(KA)
–0.30
0.84
0.86
–380
0.7
1.25
Rev G
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3
LTC3780
ELECTRICAL CHARACTERISTICS
SYMBOL
DF MAX, Boost
DF MAX, Buck
V
RUN(ON)
I
SS
V
SENSE(MAX)
V
SENSE(MIN,BUCK)
TG1, TG2 t
r
TG1, TG2 t
f
BG1, BG2 t
r
BG1, BG2 t
f
TG1/BG1 t
1D
BG1/TG1 t
2D
TG2/BG2 t
3D
BG2/TG2 t
4D
Mode
Transition 1
Mode
Transition 2
t
ON(MIN,BOOST)
t
ON(MIN,BUCK)
PARAMETER
Maximum Duty Factor
Maximum Duty Factor
RUN Pin On Threshold
Soft-Start Charge Current
Maximum Current Sense Threshold
Minimum Current Sense Threshold
TG Rise Time
TG Fall Time
BG Rise Time
BG Fall Time
TG1 Off to BG1 On Delay,
Switch C On Delay
BG1 Off to TG1 On Delay,
Synchronous Switch D On Delay
TG2 Off to BG2 On Delay,
Synchronous Switch B On Delay
BG2 Off to TG2 On Delay,
Switch A On Delay
BG1 Off to BG2 On Delay,
Switch A On Delay
BG2 Off to BG1 On Delay,
Synchronous Switch D On Delay
Minimum On-Time for Main Switch in
Boost Operation
Minimum On-Time for Synchronous
Switch in Buck Operation
Internal V
CC
Voltage
Internal V
CC
Load Regulation
EXTV
CC
Switchover Voltage
EXTV
CC
Switchover Hysteresis
EXTV
CC
Switch Drop Voltage
Nominal Frequency
Lowest Frequency
Highest Frequency
PLLIN Input Resistance
Phase Detector Output Current
f
PLLIN
< f
OSC
f
PLLIN
> f
OSC
(Note 9)
I
CC
= 20mA, V
EXTVCC
= 6V
V
PLLFLTR
= 1.2V
V
PLLFLTR
= 0V
V
PLLFLTR
= 2.4V
260
170
340
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
A
= 25°C. (Note 7) V
IN
= 15V unless otherwise noted.
CONDITIONS
% Switch C On
% Switch A On (in Dropout)
V
RUN
Rising
V
RUN
= 2V
Boost: V
OSENSE
= V
REF
– 50mV
Buck: V
OSENSE
= V
REF
– 50mV
Discontinuous Mode
C
LOAD
= 3300pF (Note 5)
C
LOAD
= 3300pF (Note 5)
C
LOAD
= 3300pF (Note 5)
C
LOAD
= 3300pF (Note 5)
C
LOAD
= 3300pF Each Driver
C
LOAD
= 3300pF Each Driver
C
LOAD
= 3300pF Each Driver
C
LOAD
= 3300pF Each Driver
C
LOAD
= 3300pF Each Driver
C
LOAD
= 3300pF Each Driver
Switch C (Note 6)
Switch B (Note 6)
l
l
MIN
TYP
99
99
MAX
UNITS
%
%
1
0.5
120
–95
1.5
1.2
160
–110
–6
50
45
45
55
80
80
80
80
250
250
200
180
2
185
–150
V
µA
mV
mV
mV
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
Internal V
CC
Regulator
V
INTVCC
∆V
LDO(LOADREG)
V
EXTVCC
∆V
EXTVCC(HYS)
∆V
EXTVCC
f
NOM
f
LOW
f
HIGH
R
PLLIN
I
PLLLPF
7V < V
IN
< 30V, V
EXTVCC
= 5V
I
CC
= 0mA to 20mA, V
EXTVCC
= 5V
I
CC
= 20mA, V
EXTVCC
Rising
l
l
5.7
5.4
6
0.2
5.7
300
150
300
200
400
50
–15
15
6.3
2
V
%
V
mV
300
330
220
440
mV
kHz
kHz
kHz
kΩ
µA
µA
Oscillator and Phase-Locked Loop
Rev G
4
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LTC3780
ELECTRICAL CHARACTERISTICS
SYMBOL
PGOOD Output
∆V
FBH
∆V
FBL
∆V
FB(HYST)
V
PGL
I
PGOOD
PGOOD Upper Threshold
PGOOD Lower Threshold
PGOOD Hysteresis
PGOOD Low Voltage
PGOOD Leakage Current
V
OSENSE
Rising
V
OSENSE
Falling
V
OSENSE
Returning
I
PGOOD
= 2mA
V
PGOOD
= 5V
5.5
–5.5
7.5
–7.5
2.5
0.1
0.3
±1
10
–10
%
%
%
V
µA
PARAMETER
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at T
A
= 25°C. (Note 7) V
IN
= 15V unless otherwise noted.
CONDITIONS
MIN
TYP
MAX
UNITS
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
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
• 34°C/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 LTC3780 is tested under pulsed load conditions such that T
J
≈
T
A
. The LTC3780E is guaranteed to meet specifications from 0°C to 85°C
junction temperature. Specifications over the –40°C to 85°C operating
junction temperature range are assured by design, characterization and
correlation with statistical process controls. The LTC3780I is guaranteed
over the –40°C to 125°C operating junction temperature range, and
the LTC3780MP is tested and guaranteed over the full –55°C to 125°C
operating junction temperature range.
Note 8:
This parameter is guaranteed by design.
Note 9:
f
OSC
is the running frequency for the application.
Rev G
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5
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