up charger and step-down converter which efficiently
charges a capacitor array up to 40V from an input supply
between 3V to 17V. When the input supply falls below the
programmable power-fail threshold, the step-up charger
operates in reverse as a synchronous step-down regulator
to power the system rail from the backup capacitor during
this power interruption/failure condition.
When charging the backup capacitor, an external low-
value sense resistor may be used to maintain an accu-
rate current limit from the input supply or implement
PowerPath
™
functionality.
The step-down converter operates at a 1MHz switching
frequency, allowing small external components to be
used. Low quiescent current during regulation maximizes
the energy usage from the backup capacitor.
L,
LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks
and PowerPath is trademarks of Analog Devices, Inc. All other trademarks are the property of
their respective owners. Protected by U.S. Patents. Including 5481178, 6580258, 6498466,
6611131, 5705919.
n
n
n
n
n
n
n
n
Bidirectional Synchronous Boost Capacitor
Charger/Buck Regulator for System Backup
Wide Input Voltage Range: 3V to 17V
Up to 40V Capacitor Voltage Storage for High
Energy Backup
2A Maximum CAP Charge Current
Integrated Power N-Channel MOSFETs
(150mΩ Top and 75mΩ Bottom)
Integrated Power N-Channel MOSFET for Output/CAP
Disconnect (50mΩ)
Input Current Limit During Charging
Fast 1MHz Switching Frequency
±1% Reference Accuracy for System Voltage Regulation
Indicator Outputs for Charge Status and Input Power Fail
Low Profile 24-lead 3mm
×
5mm QFN Package
APPLICATIONS
n
n
n
Backup Capacitor Systems
Power Failure Backup Systems
Solid-State Drives
TYPICAL APPLICATION
40V Backup System Regulating System Supply to 5V
POWER
SUPPLY
0.01
4.7µH
0.1µF
47µF
SYSTEM LOAD
Approximate Charge/Backup Time per
1mF of Storage Cap (40V Backup)
500
CHARGE TIME
BACKUP TIME WITH 2A LOAD
BACKUP TIME WITH 1A LOAD
BACKUP TIME WITH 0.5A LOAD
CLP V
IN
INDIS
GATE
35.7k
RUN
PFI
44.2k
FBSYS
12.1k
6.04k
CAPGD
PFO
GND
LTC3643
SW BOOST
CAP
INTV
CC
4.7µF
40V BACKUP
22µF
392k
CHARGE/BACKUP TIME (ms)
400
300
+
1mF
200
FBCAP
6.04k
ITH
400k
470pF
3643 TA01a
ENERGY
STORAGE
100
0
22pF
3
6
9
12
SYSTEM LOAD VOLTAGE (V)
15
3643 TA01b
3643fc
For more information
www.linear.com/LTC3643
1
LTC3643
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
CLP
I
LIM
20 SW
19 SW
18 SW
25
SGND
17 INDIS
16 INDIS
15 BOOST
14 INTV
CC
13 PFI
9 10 11 12
FBCAP
ITH
CAPGD
PFO
V
IN
............................................................. –0.3V to 17V
RUN .................................................. –0.3V to V
IN
+0.3V
CLP ............................................................ –0.3V to 17V
CAP ............................................................ –0.3V to 42V
BOOST-SW................................................... –0.3V to 4V
INTV
CC
, FBSYS, FBCAP................................ –0.3V to 4V
PFI ............................................................... –0.3V to 4V
I
LIM
.............................................–0.3V to V
INTVCC
+0.3V
PFO, CAPGD................................................ –0.3V to 6V
Operating Junction Temperature Range
(Note 2) ............................................. –40°C to 125°C
Storage Temperature Range .................. –65°C to 150°C
Lead Temperature (Soldering, 10sec).................... 260°C
NC
24 23 22 21
PGND 1
PGND 2
CAP 3
V
IN
4
V
IN
5
GATE 6
RUN 7
FBSYS 8
UDD PACKAGE
24-LEAD (3mm
×
5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 46°C/W,
θ
JC
= 5.0°C/W
EXPOSED PAD (PIN 25) IS SGND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3643EUDD#PBF
LTC3643IUDD#PBF
TAPE AND REEL
LTC3643EUDD#TRPBF
LTC3643IUDD#TRPBF
http://www.linear.com/product/LTC3643#orderinfo
PART MARKING*
LGSX
LGSX
PACKAGE DESCRIPTION
24-Lead (3mm
×
5mm) Plastic QFN
24-Lead (3mm
×
5mm) Plastic QFN
TEMPERATURE RANGE
–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.
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/.
Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
NC
2
3643fc
For more information
www.linear.com/LTC3643
LTC3643
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
J
= 25°C. V
IN
= 5V, V
RUN
= 2V unless otherwise noted. (Note 2)
SYMBOL
V
IN
I
Q-IN
R
DS(ON)
I
SW
PARAMETER
Operating Voltage
Input Quiescent Current
CONDITIONS
V
IN
CAP
Active Mode
Burst Mode
®
Operation
Shutdown Mode; RUN = 0V
V
CAP
>= V
IN
V
INTVCC
= 3.3V
V
BOOST
= 8.3V
V
CAP
= 40V, V
SW
= 0
V
CAP
= V
SW
= 40V
MIN
3.0
800
400
10
50
75
150
0.1
0.1
1
1
40
l
ELECTRICAL CHARACTERISTICS
TYP
MAX
17
40
800
20
UNITS
V
V
µA
µA
µA
mΩ
mΩ
mΩ
µA
µA
V
V
nA
µS
A
A
ns
MHz
Switch A On Resistance
Switch B On Resistance
Switch C On Resistance
Top Switch Leakage
Bottom Switch Leakage
Cap Voltage
Regulated Output Feedback Voltage
FBCAP Input Current
Error Amplifier Transconductance
Peak Inductor Current Limit
(Bottom Switch Peak Limit)
Minimum Off-Time
Switching Frequency
Input Current Limit Amplifier Regulated Voltage
Boost Charger Regulation
V
CAP
V
FBCAP
I
FBCAP
g
m
(EA)
I
LIM-BOOST
t
OFF(MIN)-BOOST
f
SW
0.594
210
l
0.6
270
3.2
70
1
0.606
±10
330
3.4
ITH = 1.2V
3.0
2.8
V
CLP-VIN
l
48.5
46
0.594
50
50
0.6
2.6
3.7
4.7
30
51.5
54
0.606
±10
3.2
4.5
5.6
mV
mV
V
nA
A
A
A
A
A
A
ns
Buck Regulator Voltage Regulation
V
FBSYS
I
FBSYS
I
LIM-BUCK
Regulated System Feedback Voltage
FBSYS Input Current
Valley Inductor Current Limit
(Bottom Switch Valley Limit)
I
LIM
= FLOAT
l
l
I
LIM
= 0V
l
2.0
2.9
3.8
I
LIM
= V
INTVCC
l
t
ON(MIN)-BUCK
INTV
CC
Regulator
Minimum On-Time
INTV
CC
Regulated Voltage
INTV
CC
UVLO
INTV
CC
Rising
l
3.0
2.6
1.12
3.2
2.75
1.2
100
0
1.0
1.1
3
20
3.4
2.9
1.28
±10
1.05
1.15
6
40
V
V
V
mV
nA
V
V
µs
µs
I/O Pins
V
RUN
RUN High Rising
RUN Hysteresis
RUN Input Current
V
PFI
PFI Input Threshold
PFI Delay Time
V
RUN
= 12V, V
IN
= 12V
Falling
Rising (100mV hysteresis)
Falling
Rising
l
l
0.95
1.05
3643fc
For more information
www.linear.com/LTC3643
3
LTC3643
The
l
denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at T
J
= 25°C. V
IN
= 5V, V
RUN
= 2V unless otherwise noted. (Note 2)
SYMBOL
PARAMETER
GATE Turn-on Time
GATE Turn-off Time
GATE Pull-Down Current
CAPGD Threshold
CAPGD Resistance
/PFO Resistance
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 LTC3643 is tested under pulsed load conditions such that
T
J
≈ T
A
. The LTC3643E is guaranteed to meet specified performance from
0°C to 85°C. Specifications over the –40°C to 125°C operating junction
FBCAP Rising
Hysteresis
CONDITIONS
To CLP-GATE > 2.5V, C
GATE
= 1nF
To CLP-GATE < 1V, C
GATE
= 1nF
l
ELECTRICAL CHARACTERISTICS
MIN
TYP
70
3
MAX
100
6
95
590
250
250
UNITS
µs
µs
µA
mV
mV
Ω
Ω
45
550
70
570
15
170
170
temperature range are assured by design, characterization and correlation
with statistical process controls. The LTC3643I is guaranteed over the
full –40°C to 125°C operating junction temperature range. 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.
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