rectional buck or boost switching regulator controller
that operates in either buck or boost mode on demand.
It regulates in buck mode from V
HIGH
-to-V
LOW
and boost
mode from V
LOW
-to-V
HIGH
depending on a control signal,
making it ideal for 48V/12V automotive dual battery sys-
tems. An accurate current programming loop regulates
the maximum current that can be delivered in either direc-
tion. The LTC3871/LTC3871-1 allows both batteries to
supply energy to the load simultaneously by converting
energy from one battery to the other.
Its proprietary constant-frequency current mode
architecture enhances the signal-to-noise ratio enabling
low noise operation and provides excellent current
matching between phases. Additional features include
discontinuous or continuous mode of operation, OV/UV
monitors, independent loop compensation for buck and
boost operation, accurate output current monitoring and
overcurrent protection. The LTC3871 and LTC3871-1
have different current limit foldback characteristics.
All registered trademarks and trademarks are the property of their respective owners.
n
n
n
n
n
n
n
n
Unique Architecture Allows Dynamic Regulation of
Input Voltage, Output Voltage or Current
V
HIGH
Voltages Up to 100V
V
LOW
Voltages Up to 30V
Synchronous Rectification: Up to 97% Efficiency
ADI-Proprietary Advanced Current Mode Control
±1% Voltage Regulation Accuracy Over Temperature
Accurate, Programmable Output Current Monitoring
and Regulation for Both Buck and Boost Operation
Selectable Buck and Boost Current Sense Limits
Programmable DRV
CC
/EXTV
CC
Optimizes Efficiency
Programmable V
HIGH
UV and OV Thresholds
Programmable V
LOW
OV Threshold
Phase-Lockable Frequency: 60kHz to 460kHz
Multiphase/Multi-ICs Operation Up to 12 Phases
Selectable CCM/DCM Modes
Thermally Enhanced 48-Lead LQFP Package
Automotive 48V/12V Dual Battery Systems
Backup Power Systems
APPLICATIONS
n
n
TYPICAL APPLICATION
V
HIGH
26V TO 58V
High Efficiency Bidirectional Charger/Power Supply
PGATE
OV
HIGH
UV
HIGH
V
HIGH
EXTV
CC
VFB
LOW
Buck-to-Boost Transition
BUCK
BUCK BOOST
ITH
HIGH
SNS1
–
SNSD1
+
SNSA1
+
BST1
LTC3871/
LTC3871-1
TG1
SW1
BG1
VFB
HIGH
V
LOW
12V
BATTERY
DRV
CC
ITH
LOW
SS
V
LOW
5V/DIV
I
L
5A/DIV
V
HIGH
10V/DIV
SW
50V/DIV
50 /DIV
3871 TA01b
BUCK
BOOST
BUCK
IMON
V
LOW
FREQ
SNSD2
+
SNSA2
+
BST2
TG2
SW2
BG2
3871 TA01a
SNS2
–
DRV
CC
OV
LOW
SGND
V5
PGND
DRV
CC
PINS NOT SHOWN IN THIS CIRCUIT:
CLKOUT, DRVSET,
FAULT,
ILIM, MODE,
PHSMD, RUN, SETCUR AND SYNC.
Rev. B
Document Feedback
For more information
www.analog.com
1
LTC3871/LTC3871-1
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
SNSA1
+
SNS1
–
SNSD1
+
PHSMD
MODE
FREQ
SYNC
CLKOUT
N/C
TG1
SW1
BOOST1
SS 1
VFB
LOW
2
ITH
LOW
3
ITH
HIGH
4
VFB
HIGH
5
V5 6
SGND 7
OV
HIGH
8
UV
HIGH
9
OV
LOW
10
IMON 11
SETCUR 12
48
47
46
45
44
43
42
41
40
39
38
37
V
HIGH
....................................................... –0.3V to 100V
Top Side Driver Voltages
(BOOST1, BOOST2) .............................. –0.3V to 111V
Switch Voltage (SW1, SW2) ....................... –5V to 100V
Current Sense Voltages
(SNSA
+
, SNS
–
, SNSD
+
Channels 1 and 2) ... –0.3V to 34V,
–2V to 34V for < 100μsec
(BOOST1-SW1), (BOOST2-SW2) ...........–0.3V to 11V
EXTV
CC
.....................................................–0.3V to 34V,
–0.8V to 34V for < 100μsec
DRV
CC
........................................................–0.3V to 11V
VFB
HIGH
, VFB
LOW
........................................ –0.3V to V5
MODE, SS Voltages...................................... –0.3V to V5
RUN ............................................................. –0.3V to 6V
FAULT,
SETCUR, Voltages ........................... –0.3V to V5
ILIM, DRVSET, BUCK Voltages .................... –0.3V to V5
OV
HIGH
, UV
HIGH
, OV
LOW
Voltages ................ –0.3V to 6V
SYNC, PHSMD Voltages .............................. –0.3V to V5
Operating Junction Temperature
Range (Notes 2, 3) ............................. –40°C to 150°C
Storage Temperature Range .................. –65°C to 150°C
DRV
CC
/EXTV
CC
Peak Current ...............................100mA
49
GND
36
35
34
33
32
31
30
29
28
27
26
25
BG1
PGND1
N/C
PGATE
N/C
V
HIGH
N/C
DRV
CC
SGND
EXTV
CC
PGND2
BG2
LXE PACKAGE
48-LEAD (7mm
×
7mm) PLASTIC LQFP
T
JMAX
= 150°C,
θ
JA
= 36°C/W
EXPOSED PAD (PIN 49) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3871ELXE#PBF
LTC3871ILXE#PBF
LTC3871HLXE#PBF
LTC3871ELXE-1#PBF
LTC3871ILXE-1#PBF
LTC3871HLXE-1#PBF
PART MARKING*
LTC3871
LTC3871
LTC3871
LTC3871-1
LTC3871-1
LTC3871-1
PACKAGE DESCRIPTION
48-Lead (7mm × 7mm) Plastic LQFP
48-Lead (7mm × 7mm) Plastic LQFP
48-Lead (7mm × 7mm) Plastic LQFP
48-Lead (7mm × 7mm) Plastic LQFP
48-Lead (7mm × 7mm) Plastic LQFP
48-Lead (7mm × 7mm) Plastic LQFP
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
–40°C to 150°C
–40°C to 125°C
–40°C to 125°C
–40°C to 150°C
Contact the factory for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Tape and reel specifications.
Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix.
SNSA2
+
13
SNS2
–
14
SNSD2
+
15
BUCK 16
ILIM 17
RUN 18
FAULT
19
DRVSET 20
N/C 21
TG2 22
SW2 23
BOOST2 24
Rev. B
2
For more information
www.analog.com
LTC3871/LTC3871-1
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
A
= 25°C, V
HIGH
= 50V, V
RUN
= 5V unless otherwise noted (Note 2).
SYMBOL
V
HIGH
V
LOW
PARAMETER
V
HIGH
Supply Voltage Range
V
LOW
Supply Voltage Range
V
LOW
Regulated Feedback Voltage
V
HIGH
Regulated Feedback Voltage
V
LOW
EA Feedback Current
V
HIGH
EA Feedback Current
Reference Voltage Line Regulation
V
LOW
/V
HIGH
Voltage Load Regulation
V
HIGH
> 5V
(Note 4); ITH
LOW
Voltage = 1.5V
(Note 4); ITH
HIGH
Voltage = 0.5V
(Note 4)
(Note 4)
(Note 4); V
HIGH
= 7V to 80V
Measured in Servo Loop;
∆I
TH
Voltage = 1V to 1.5V
Measured in Servo Loop;
∆I
TH
Voltage = 1V to 0.5V
g
m-buck
g
m-boost
I
Q
Transconductance Amplifier g
m-buck
Transconductance Amplifier g
m-boost
V
HIGH
DC Supply Current
Shutdown (V
HIGH
)
Undervoltage Lockout
Undervoltage Hysteresis
RUN Pin On Threshold
RUN Pin On Hysteresis
RUN Pin Source Current
RUN Pin Source Current
I
SS
I
SNSA+ 1,2
I
SNSD+ 1,2
I
SNS– 1,2
Soft-Start Charging Current
Current Sensing Pins Current
Current Sensing Pins Current
Current Sensing Pins Current
Total DC Sense Signal Gain
ILIM Pin Input Resistance
I
SETCUR
Current to Program Initial Current Limit
IMON Current Proportional to V
LOW
at
Max Current
IMON Zero Current Voltage
Sense Pin to IMON Gain
TG Pull-Up On-Resistance
TG Pull-Down On-Resistance
BG Driver Pull-Up On-Resistance
BG Driver Pull-Down On-Resistance
Total DC Sense Signal Gain
Maximum Duty Cycle
R
SENSE
Configuration
Buck Mode
Boost Mode
96
V
ILIM
= 0V, 1/4 V
V5
, Float
V
ILIM
= 3/4 V
V5
, V
V5
V
ILIM
= Float; R
SENSE
= 3mΩ
l
l
l
l
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
5
1.2
1.188
1.185
TYP
MAX
100
30
UNITS
V
V
V
V
nA
nA
%
%
%
mmho
mmho
1.200
1.200
–115
–115
0.02
0.01
–0.01
2
1
8
140
1.212
1.215
–200
–200
0.2
0.2
–0.2
(Note 4); ITH
LOW
= 1.5V; Sink/Source 5µA
(Note 4); ITH
HIGH
= 0.5V; Sink/Source 5µA
(Note 5)
V
RUN
= 0V; V
HIGH
= 50V
V5 Ramping Down
V
RUN
Rising
V
RUN
< 1.2
V
RUN
> 1.3
V
SS
= 1.2V
l
l
14
4.5
1.35
mA
µA
V
V
V
mV
µA
µA
3.7
1.1
1
3
0.9
4.15
0.5
1.22
80
2
6.5
1.25
0.1
0.01
1.5
1.7
±1
±1
µA
µA
µA
mA
V/V
kΩ
DCR Configuration
6.75
5
100
7.5
8.25
±10
1.125
1.25
38
19
5
2.5
5
2.5
4
98
92
1.375
µA
%
V
V/V
V/V
Ω
Ω
Ω
Ω
V/V
%
%
Rev. B
For more information
www.analog.com
3
LTC3871/LTC3871-1
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
A
= 25°C, V
HIGH
= 50V, V
RUN
= 5V unless otherwise noted (Note 2).
SYMBOL
V
SENSE(MAX)
(DCR Sensing)
PARAMETER
Maximum Current Sense Threshold
(Buck and Boost Mode)
CONDITIONS
0°C to 150°C
V
ILIM
= 0V
V
ILIM
= 1/4 V
V5
V
ILIM
= Float
V
ILIM
= 3/4 V
V5
V
ILIM
= V
V5
(LTC3871)
V
ILIM
= V
V5
(LTC3871-1)
0°C to 150°C
V
ILIM
= 0V
V
ILIM
= 1/4 V
V5
V
ILIM
= Float
V
ILIM
= 3/4 V
V5
V
ILIM
= V
V5
(LTC3871)
V
ILIM
= V
V5
(LTC3871-1)
–40°C to 150°C
V
ILIM
= 0V
V
ILIM
= 1/4 V
V5
V
ILIM
= Float
V
ILIM
= 3/4 V
V5
V
ILIM
= V
V5
(LTC3871)
V
ILIM
= V
V5
(LTC3871-1)
–40°C to 150°C
V
ILIM
= 0V
V
ILIM
= 1/4 V
V5
V
ILIM
= Float
V
ILIM
= 3/4 V
V5
V
ILIM
= V
V5
(LTC3871)
V
ILIM
= V
V5
(LTC3871-1)
(Note 6)
(Note 6)
(Note 6) C
LOAD
= 3300pF Each Driver
(Note 6) C
LOAD
= 3300pF Each Driver
6V < V
DRVCC
< 10V
I
V5
= 0mA to 20mA
12V < V
EXTVCC
< 30V, V
DRVSET
= V
V5
12V < V
EXTVCC
< 30V, V
DRVSET
= 3/4 V
V5
12V < V
EXTVCC
< 30V, V
DRVSET
= Float
12V < V
EXTVCC
< 30V, V
DRVSET
= 1/4 V
V5
12V < V
EXTVCC
< 30V, V
DRVSET
= 0V
I
CC
= 0mA to 20mA, V
EXTVCC
= 10V
EXTV
CC
Ramping Positive
V
PHSMD
= 0V
V
PHSMD
= 1/4 V
V5
V
PHSMD
= Float
V
PHSMD
= 3/4 V
V5
V
PHSMD
= V
V5
5.3
9.5
8.5
7.5
6.5
5.5
MIN
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
ELECTRICAL CHARACTERISTICS
TYP
10
20
30
40
50
50
12.5
25
37.5
50
62.5
62.5
10
20
30
40
50
50
12.5
25
37.5
50
62.5
62.5
60
60
60
60
MAX
14.5
24
33.5
44.5
55.5
58.5
18.2
30
41.9
55.6
69.4
73.1
14.5
24
33.5
44.5
55.5
58.5
18.2
30
41.9
55.6
69.4
73.1
UNITS
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
ns
ns
ns
ns
V
%
V
V
V
V
V
%
V
%
Deg
Deg
Deg
Deg
Deg
8
17
26.5
36
44.5
44.5
10
21.3
33.2
45
55.6
55.6
7
16
26
35
42
42
8.8
20
32.5
43.8
52.5
52.5
V
SENSE(MAX)
(R
SENSE
Sensing)
Maximum Current Sense Threshold
(Buck and Boost Mode)
V
SENSE(MAX)
(DCR Sensing)
Maximum Current Sense Threshold
(Buck and Boost Mode)
V
SENSE(MAX)
(R
SENSE
Sensing)
Maximum Current Sense Threshold
(Buck and Boost Mode)
TG t
r
TG t
f
BG t
r
BG t
f
V
DRVCC
Top Gate Rise Time
Top Gate Fall Time
Bottom Gate Rise Time
Bottom Gate 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
V5 Regulation Voltage
V5 Load Regulation
DRV
CC
Regulation Voltage
DRV
CC
Load Regulation
EXTV
CC
Switchover Voltage
V
EXTVCC
EXTV
CC
Hysteresis
CLKOUT Phasing Phase Relative to Channel 1
5.5
5.7
0.5
1
10
10.5
9
9.5
8
8.5
7
7.5
6
6.5
0.2
1
DRV
CC
–0.5V
10
60
60
90
45
240
Rev. B
4
For more information
www.analog.com
LTC3871/LTC3871-1
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
A
= 25°C, V
HIGH
= 50V, V
RUN
= 5V unless otherwise noted (Note 2).
SYMBOL
SYNC Phasing
PARAMETER
Phase Relative to Channel 1
CONDITIONS
V
PHSMD
= 0V
V
PHSMD
= 1/4 V
V5
V
PHSMD
= Float
V
PHSMD
= 3/4 V
V5
V
PHSMD
= V
V5
Channel to
Channel Phasing
Channel 1 to Channel 2
V
PHSMD
= 0V
V
PHSMD
= 1/4 V
V5
V
PHSMD
= Float
V
PHSMD
= 3/4 V
V5
V
PHSMD
= V
V5
CLKOUT
HI
CLKOUT
LO
V
SYNC
Clock Output High Voltage
Clock Output Low Voltage
Sync Input Threshold
Nominal Frequency
f
LOW
f
HIGH
Low Fixed Frequency
High Fixed Frequency
Synchronizable Frequency
SYNC Input Resistance
I
FREQ
Frequency Setting Current
FAULT
Voltage Low
FAULT
Leakage Current
FAULT
Delay
V
LOW
OV Comparator Threshold
V
LOW
OV Comparator Hysteresis
V
HIGH
OV Comparator Threshold
V
HIGH
OV Comparator Hysteresis
V
HIGH
UV Comparator Threshold
V
HIGH
UV Comparator Hysteresis
BUCK Pin Pull-Up Resistance
V
UVHIGH
< 1.2V
BUCK Pin to V5
V
OVHIGH
> 1.2V
1.15
V
OVLOW
> 1.2V
1.15
I
FAULT
= 2mA
V
FAULT
= 5.5V
Going Low
1.15
125
1.2
5
1.2
5
1.2
5
200
1.25
1.25
1.25
l
ELECTRICAL CHARACTERISTICS
MIN
TYP
0
90
0
0
0
180
180
180
180
120
MAX
UNITS
Deg
Deg
Deg
Deg
Deg
Deg
Deg
Deg
Deg
Deg
V
I
LOAD
= 0.5mA
I
LOAD
= –0.5mA
V
SYNC
Rising
V
SYNC
Falling
R
FREQ
= 51.1kΩ
R
FREQ
= ≤20kΩ
R
FREQ
= 117kΩ
SYNC = External Clock
l
5.2
2
5.5
0
0.2
1.2
V
V
V
kHz
kHz
kHz
kHz
kΩ
µA
V
µA
µs
V
µA
V
µA
V
µA
kΩ
180
40
450
60
200
50
500
100
220
60
550
460
18
20
0.1
22
0.3
±1
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Ratings for extended periods may affect device reliability
and lifetime.
Note 2:
The LTC3871/LTC3871-1 is tested under pulsed load conditions
such that T
J
≈ T
A
. The LTC3871/LTC3871-1E is guaranteed to meet
performance specifications from 0°C to 85°C junction temperature.
Specifications over the –40°C to 125°C operating junction temperature
range are assured by design, characterization and correlation with
statistical process controls. The LTC3875I is guaranteed over the
–40°C to 125°C operating junction temperature range. The LTC3871/
LTC3871-1H is guaranteed over the full –40°C to 150°C operating
junction temperature range. High junction temperature degrades operating
lifetimes; operating lifetime is derated for junction temperatures greater
than 125°C. Note that the maximum ambient temperature consistent with
these specifications is determined by specific operating conditions in
conjunction with board layout, the rated package thermal impedance and
other environmental factors.
Note 3:
T
J
is calculated from the ambient temperature T
A
and
power dissipation P
D
according to the following formula: T
J
= T
A
+
(P
D
• 36°C/W).
Note 4:
The LTC3871/LTC3871-1 is tested in a feedback loop that servos
V
ITHHIGH
and V
ITHLOW
to a specified voltage and measures the resultant
V
FBHIGH
and V
FBLOW
, respectively.
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
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