switching regulator controller capable of operating from
a 2.5V to 60V supply.
The LT3840’s low quiescent current, when configured for
user selectable Burst Mode operation, helps extend run
time in battery-powered systems by increasing efficiency
at light loads. The LT3840 uses a constant frequency,
current mode architecture. High current applications are
possible with large N-channel gate drivers capable of
driving multiple low R
DS(ON)
MOSFETs.
An integrated buck-boost switching regulator generates
a 7.5V bias supply voltage for MOSFET gate drive and IC
power allowing higher efficiency operation over the entire
input voltage range and eliminating the need for an external
bias voltage. An accurate current limit set point regulates
the maximum output current. A current monitor reports
the average output current.
L,
LT, LTC, LTM, Linear Technology, Burst Mode, and the Linear logo are registered
trademarks of Linear Technology Corporation. All other trademarks are the property of their
respective owners.
n
n
n
n
n
n
n
n
n
n
Wide Input Range: 2.5V to 60V
Integrated Buck-Boost Supply for 7.5V MOSFET
Gate Drive
Programmable Constant-Current Operation with
Current Monitor Output
Low I
Q
: 75µA, 12V
IN
to 3.3V
OUT
Selectable Low Output Ripple Burst Mode
®
Operation
V
OUT
Up to 60V
Adjustable and Synchronizable: 50kHz to 1MHz
Internal OVLO Protects for Input Transients Up to 80V
Accurate Input Overvoltage and Undervoltage Threshold
Programmable Soft-Start with Voltage Tracking
Power Good and Output OVP
28-Lead TSSOP and 38-Lead 4mm × 6mm QFN Packages
applicaTions
n
n
n
Automotive Supplies
Industrial Systems
Distributed DC Power Systems
Typical applicaTion
High Efficiency Synchronous Step-Down Converter
V
IN
4V TO 60V
68µF
×2
1µF
33µH
100
95
AUXBST AUXSW1
EN
V
IN
AUXVIN
UVLO
OVLO
PG
SYNC
MODE
RT
V
C
49.9k
20k
1500pF
100pF
IMON
ICOMP
7.68k
470pF
3840 TA01a
12V
IN
to 3.3V
OUT
Efficiency
AUXSW2
INTV
CC
90
EFFICIENCY (%)
1.5µH
2m
V
OUT
3.3V
20A
330µF
×2
4.7µF
85
80
75
70
65
60
55
50
0
5
10
15
LOAD CURRENT (A)
20
3840 TA01b
LT3840
BOOST
1µF
TG
SW
BG
SENSE
+
SENSE
–
FB
GND
ICTRL
16.9k
10k
TK/SS
2200pF
3840fa
For more information
www.linear.com/LT3840
1
LT3840
absoluTe MaxiMuM raTings
(Note 1)
AUXVIN, V
IN
, EN and UVLO ....................... –0.3V to 80V
PG .............................................................. –0.3V to 25V
MODE........................................................... –0.3V to 9V
SENSE
+
and SENSE
–
.................................. –0.3V to 60V
SENSE
+
to SENSE
–
...........................................–1V to 1V
OVLO, V
C
, FB, SYNC, TK/SS and ICTRL ....... –0.3V to 6V
Junction Temperature Range
LT3840E (Note 2) .............................. –40°C to 125°C
LT3840I ............................................. –40°C to 125°C
LT3840H ............................................ –40°C to 150°C
LT3840MP ......................................... –55°C to 150°C
Lead Temperature (Soldering, 10 sec)
TSSOP Only .......................................................... 300°C
Storage Temperature............................. –65°C to 150°C
pin conFiguraTion
TOP VIEW
AUXSW1
AUXBST
PGND
TOP VIEW
AUXSW1
PGND
AUXVIN
SYNC
RT
TK/SS
FB
V
C
PG
1
2
3
4
5
6
7
8
9
29
GND
28 AUXBST
27 AUXSW2
26 INTVCC
25 BG
24 BGRTN
23 BOOST
22 TG
21 SW
20 SENSE
–
19 SENSE
+
18 ICOMP
17 ICTRL
16 IMON
15 GND
AUXSW2
NC
NC
38 37 36 35 34 33 32
AUXVIN 1
NC 2
SYNC 3
RT 4
NC 5
TK/SS 6
FB 7
V
C
8
PG 9
NC 10
MODE 11
OVLO 12
13 14 15 16 17 18 19
V
IN
ICTRL
NC
GND
UVLO
IMON
EN
39
GND
31 NC
30 INTV
CC
29 BG
28 BGRTN
27 NC
26 BOOST
25 TG
24 SW
23 NC
22 SENSE
–
21 SENSE
+
20 ICOMP
MODE 10
OVLO 11
UVLO 12
EN 13
V
IN
14
FE PACKAGE
28-LEAD PLASTIC TSSOP
θ
JA
= 30°C/W,
θ
JC
= 10°C/W
EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB
UFE PACKAGE
38-LEAD (4mm × 6mm) PLASTIC QFN
θ
JA
= 38°C/W,
θ
JC
= 4°C/W
EXPOSED PAD (PIN 39) IS GND, MUST BE SOLDERED TO PCB
orDer inForMaTion
LEAD FREE FINISH
LT3840EFE#PBF
LT3840IFE#PBF
LT3840HFE#PBF
LT3840MPFE#PBF
LT3840EUFE#PBF
LT3840IUFE#PBF
TAPE AND REEL
LT3840EFE#TRPBF
LT3840IFE#TRPBF
LT3840HFE#TRPBF
LT3840MPFE#TRPBF
LT3840EUFE#TRPBF
LT3840IUFE#TRPBF
PART MARKING*
LT3840FE
LT3840FE
LT3840FE
LT3840FE
3840
3840
PACKAGE DESCRIPTION
28-Lead Plastic TSSOP
28-Lead Plastic TSSOP
28-Lead Plastic TSSOP
28-Lead Plastic TSSOP
38-Lead (4mm × 6mm) Plastic QFN
38-Lead (4mm × 6mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
–40°C to 150°C
–55°C to 150°C
–40°C to 125°C
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Consult LTC Marketing for information on nonstandard lead based finish parts.
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/
3840fa
2
For more information
www.linear.com/LT3840
NC
LT3840
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C.
PARAMETER
Input Supply
V
IN
Minimum Operating Voltage
V
IN
Supply Current
V
IN
Burst Mode Current
V
IN
Shutdown Current
AUXV
IN
Minimum Operating Voltage
AUXV
IN
Overvoltage Lockout
AUXV
IN
Supply Current
AUXV
IN
Burst Mode Current
AUXV
IN
Shutdown Current
EN Enable Threshold (Rising)
EN Hysteresis
EN Pin Bias Current
UVLO Enable Threshold (Rising)
UVLO Hysteresis
UVLO Pin Bias Current
OVLO Threshold (Rising)
OVLO Hysteresis
OVLO Pin Bias Current
Voltage Regulation
Regulated FB Voltage
Regulated FB Voltage
FB Overvoltage Protection
FB Overvoltage Protection Hysteresis
FB Input Bias Current
FB Voltage Line Regulation
FB Error Amp Transconductance
FB Error Amp Sink/Source Current
Peak Current Limit Sense Voltage
Peak Current Limit Sense Voltage
TK/SS Charge Current
Current Regulation
Sense Common Mode Range
Average Current Limit Sense Voltage
IMON Voltage
ICTRL Current
Reverse Protect Sense Voltage
Reverse Current Sense Voltage Offset
Sense Input Current
Oscillator
Switching Frequency
R
T
= 49.9k
R
T
= 348k
R
T
= 13.7k
l
l
l
elecTrical characTerisTics
CONDITIONS
MIN
TYP
MAX
2.5
30
1
2.5
UNITS
V
µA
µA
µA
V
V
µA
µA
µA
V
mV
nA
V
mV
nA
V
mV
nA
V
V
%
%
nA
%/V
µS
µA
V
MODE
= 0V
V
EN
= 0.3V
(Note 3)
V
MODE
= 0V
V
EN
= 0.3V
l
l
l
20
20
0.1
60
300
0.1
0.1
1.25
30
2
1.25
45
1
1.25
125
1
1.250
1.250
12
2.5
5
1
1.30
l
1.20
V
EN
= 1.25V
l
1.20
1.30
V
UVLO
= 1.25V
l
1.20
1.30
V
OVLO
= 1.25V
E- and I-Grade
MP- and H-Grade
% Above FB Voltage
l
l
l
1.237
1.232
8
1.263
1.263
16
20
0.02
2.5V ≤ V
IN
≤ 60V
0.002
300
±25
0% Duty Cycle
100% Duty Cycle
80
95
60
9
110
mV
mV
µA
0
47.5
0.95
50
40
1.00
0.4
7
–50
5
300
280
300
50
1000
1.2
60
52.5
1.05
V
mV
mV
V
V
µA
mV
mV
µA
V
ICTRL
= Open
V
ICTRL
= 800mV
V
SENSE
= 50mV
V
SENSE
= 20mV
V
ICTRL
= 1V
V
MODE
= 7.5V
V
MODE
= V
FB
or V
MODE
= 0V
SENSE
+
= SENSE
–
= 12V
l
l
320
kHz
kHz
kHz
V
3840fa
SYNC Threshold
For more information
www.linear.com/LT3840
3
LT3840
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C.
PARAMETER
Power Good
PG Threshold as a Percentage of V
FB
PG Hysteresis as a Percentage of V
FB
PG Leakage
PG Sink Current
MOSFET Gate Drivers
Non-Overlap Time TG to BG
Non-Overlap Time BG to TG
TG Minimum On Time
TG Minimum Off Time
TG Maximum Duty Cycle
TG, BG Drive On Voltage
TG, BG Drive Off Voltage
TG, BG Drive Rise Time
TG, BG Drive Fall Time
BOOST UVLO (Rising)
BOOST UVLO Hysteresis
Internal Auxiliary Supply
INTV
CC
Regulation Voltage
INTV
CC
UVLO Threshold (Rising)
INTV
CC
UVLO Hysteresis
INTV
CC
Current in Shutdown
INTV
CC
Output Current
INTV
CC
Burst Mode Current
V
EN
= 0.3V
2.5V ≤ V
IN
≤ 60V (Note 4)
V
MODE
= 0V
l
l
elecTrical characTerisTics
CONDITIONS
V
FB
Rising
V
PG
= 5V
V
PG
= 0.3V
l
l
MIN
87
TYP
90
2.5
0.1
MAX
93
1
UNITS
%
%
µA
µA
ns
ns
ns
ns
%
V
mV
ns
ns
V
mV
35
65
75
75
150
240
R
T
= 49.9k
99
7.5
5
C
TG
= C
BG
= 3300pF
C
TG
= C
BG
= 3300pF
V
BOOST
- V
SW
4.5
20
20
5.3
350
7.25
6.25
7.5
6.5
300
6
100
60
7.75
6.75
V
V
mV
µA
mA
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:
The LT3840E is guaranteed to meet performance specifications
from 0°C to 125°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
LT3840I is guaranteed over the –40°C to 125°C operating junction
temperature range. The LT3840H is guaranteed over the full –40°C to
150°C operating junction temperature range. The LT3840MP is 100%
tested and guaranteed over the –55°C to 150°C temperature range. High
junction temperatures degrade operating lifetimes; Operating lifetime is
derated for junction temperatures greater than 125°C.
Note 3:
Supply current specification does not include switch drive
currents. Actual supply currents will be higher.
Note 4:
Specification is not tested but is guaranteed by design,
characterization and correlation with statistical process controls.
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