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LTC3128
3A Monolithic Buck-Boost
Supercapacitor Charger and
Balancer with Accurate Input Current Limit
FEATURES
DESCRIPTION
n ±2% Accurate Average Input Current Limit
Programmable Up to 3A
n Programmable Maximum Capacitor Voltage Limit
n Active Charge Balancing for Fast Charging of
Unmatched Capacitors
n Charges Single or Stacked Capacitors
n VIN Range: 1.73V to 5.5V
n VOUT Range: 1.8V to 5.5V
n <2µA Quiescent Current from VOUT When Charged
n Output Disconnect in Shutdown: <1µA IQ Shutdown
n Power-Good Comparator
n Power Failure Indicator
n Thermally Enhanced 20-Lead (4mm × 5mm × 0.75mm)
QFN and 24-Lead TSSOP Packages
APPLICATIONS
n Supercapacitor Based Backup Power
n Memory Backup
n Servers, RAID, RF Systems
n Industrial, Communications, Computing
The LTC®3128 is a highly efficient, buck-boost DC/DC
supercapacitor charger. It operates efficiently from input
voltages above, below or equal to the output voltage. The
LTC3128 incorporates accurate programmable average
input current limit, active charge balancing and program-
mable maximum capacitor voltage. This combination of
features makes the LTC3128 ideal for safely charging and
protecting large capacitors in backup power systems. The
input current limit and maximum capacitor voltage are each
programmed using a single resistor. Average input current
is accurately controlled over a 0.5A to 3A programmable
range while the individual maximum capacitor voltage can
be set from 1.8V to 3.0V.
Other features of the LTC3128 include <2µA quiescent
current from VOUT in Burst Mode®operation, accurate
power-good and power failure indicators, and thermal
overload protection. The LTC3128 is offered in low profile,
thermally enhanced 20-Lead 4mm × 5mm × 0.75mm QFN
and 24-Lead TSSOP packages.
L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks
and PowerPath is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
TYPICAL APPLICATION
Wide VIN (3A Programmed Input Current) to 4.2V
3.3µH
1.7V TO 5.5V
UP TO 3.0A
10µF
10µF
SW1 SW2
RSENP
RSENS
VVOOUUTTPS
RVIUNNLTC3128MID
PFI
PFO
FB
PGOOD
MAXV PROG
GND
127k
VOUT = 4.2V
1.87M
C1a
940mF
C1
C1b
940mF
470pF 3.57k 301k
3128 TA01
C1: Murata DMF3Z5R5H474M3DTA0
Stacked Output Capacitors Charging Waveform
VOUT
2.0V/DIV
MID
2.0V/DIV
IIN
2.0A/DIV
ILOAD
2.0A/DIV
2 SECONDS/DIV
3128 TA01b
For more information www.linear.com/LTC3128
3128f
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LTC3128
ABSOLUTE MAXIMUM RATINGS
(Note 1)
VIN, RSENP, VOUTP, MID Voltage................... –0.3V to 6V
RSENS, VOUTS Voltage.................................. –0.3V to 6V
RSENS DC Current.....................................................–4A
SW1, SW2 DC Voltage.................................. –0.3V to 6V
SW1, SW2 Pulsed (<100ns) Voltage..............–1.0V to 7V
PGOOD, PFO, RUN Voltage........................... –0.3V to 6V
PROG, MAXV, FB, PFI Voltage...................... –0.3V to 6V
PGOOD, PFO DC Current.........................................15mA
Operating Junction Temperature Range
(Notes 2, 4)............................................. –40°C to 125°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
FE Only.............................................................. 300°C
PIN CONFIGURATION
TOP VIEW
SW1 1
RSENP 2
RSENS 3
RUN 4
PROG 5
NC 6
20 19 18 17
16 VOUTP
15 VOUTP
21 14 VOUTS
GND 13 MID
12 PGOOD
11 FB
7 8 9 10
UFD PACKAGE
20-LEAD (4mm × 5mm) PLASTIC QFN
TJMAX = 125°C, θJA = 43°C/W
EXPOSED PAD (PIN 21) IS GND, MUST BE SOLDERED TO PCB (NOTE 5)
SW1 1
GND 2
GND 3
SW1 4
RSENP 5
RSENS 6
RUN 7
PROG 8
NC 9
NC 10
VIN 11
GND 12
TOP VIEW
25
GND
24 SW2
23 SW2
22 NC
21 VOUTP
20 VOUTP
19 VOUTS
18 MID
17 PGOOD
16 FB
15 MAXV
14 PFI
13 PFO
FE PACKAGE
24-LEAD PLASTIC TSSOP
TJMAX = 125°C, θJA = 38°C/W
EXPOSED PAD (PIN 25) SHOULD BE SOLDERED TO PCB (NOTE 5)
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
LTC3128EUFD#PBF
LTC3128EUFD#TRPBF 3128
20-Lead (4mm × 5mm) Plastic QFN
LTC3128IUFD#PBF
LTC3128IUFD#TRPBF 3128
20-Lead (4mm × 5mm) Plastic QFN
LTC3128EFE#PBF
LTC3128EFE#TRPBF
LTC3128FE
24-Lead Plastic TSSOP
LTC3128IFE#PBF
LTC3128IFE#TRPBF
LTC3128FE
24-Lead Plastic TSSOP
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard 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/
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
3128f
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LTC3128
E LECTRICAL CHARACTERISTICS The l denotes specifications that apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C. (Note 2) VIN = 3.3V, VOUT = 4.8V, unless otherwise noted.
PARAMETER
CONDITIONS
MIN TYP MAX UNITS
Input Operating Range
l 1.73
5.5 V
Programmed Output Voltage Range
l 1.8
5. 5 V
FB Voltage
l 0.565 0.580 0.590
V
FB Voltage Hysteresis
8.5 mV
FB Input Current
FB > 0.590V
0.5 2
nA
Switching Frequency
While Charging
l 1.00 1.20 1.40
MHz
Power Good Rising Threshold Voltage
Measured as a % of FB Voltage
l 94.50 96.75 99.00
%FB
Power Good Hysteresis
Measured as a % of FB Voltage
3.6 %
Power Good Voltage Low
Power Good Leakage Current
IPGOOD = 5mA
PGOOD = 5.5V
200
0.1 1
mV
µA
PFI Falling Threshold
l 0.565 0.580 0.590
V
PFI Hysteresis Current
PFI Input Current
PFO Voltage Low
PFO Leakage Current
VPFI < 0.565V
VPFI > 0.590V
IPFO = 5mA
PFO = 5.5V
0.2
0.5 2
200
0.1 1
µA
nA
mV
µA
Maximum Capacitor Voltage – Rising
Maximum Capacitor Voltage Hysteresis
RMAXV = 125k, –40°C to 125°C (Note 7)
RRMMAAXXVV
=
=
125k,
113k,
0°C to
–40°C
85°C (Notes 6,
to 125°C (Note
7)
7)
RMAXV = 113k, 0°C to 85°C (Notes 6, 7)
l 2.350
l 2.400
l 2.150
l 2.170
2.500
2.500
2.260
2.260
120
2.650
2.600
2.380
2.350
200
V
V
V
V
mV
MAXV Pin Current
20 µA
VIN Quiescent Current – Sleep
VOUT Quiescent Current – Sleep
VIN Quiescent Current – Shutdown
VOUT Quiescent Current – Shutdown
VOUT Quiescent Current – Shutdown
VIN Quiescent Current – Active
VIN Quiescent Current – UVLO
VOUT Quiescent Current – UVLO
Input Current Limit
VRUN = 3.3V, VFB > 0.590V
VRUN = 3.3V, Not Balancing, VFB > 0.590V
VRUN = 3.3V, Balancing, VFB > 0.590V
VRUN = 0V, Not Including SW Leakage
VRUN = 0V, Not Including SW Leakage
VRUN = 0V, VIN = 0V, Not Including SW Leakage
VRUN = 3.3V (Note 3)
VRUN = 1.5V, VIN = 1.5V, Not Including SW Leakage
VRUN = 1.5V, VIN = 1.5V, Not Including SW Leakage
RPROG = 22.1k (Notes 3, 7)
RRPPRROOGG
=
=
22.1k (Notes 3, 7)
11k (Notes 3, 7)
RPROG = 11k (Notes 3, 7)
RPROG = 5.49k (Notes 3, 7)
RRPPRROOGG
=
=
5.49k
3.57k
(Notes
(Notes
3,
3,
7)
7)
RPROG = 3.57k (Notes 3, 7)
l
l
l
l
489
475
985
958
1973
1923
3034
2951
14
1.9
100
0.6
0.4
0.4
600
25
1
497
497
1000
1000
2003
2003
3081
3081
1
1
1
2
504
515
1015
1035
2033
2075
3127
3185
µA
µA
µA
µA
µA
µA
µA
µA
µA
mA
mA
mA
mA
mA
mA
mA
mA
For more information www.linear.com/LTC3128
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LTC3128
E LECTRICAL CHARACTERISTICS The l denotes specifications that apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C. (Note 2) VIN = 3.3V, VOUT = 4.8V, unless otherwise noted.
PARAMETER
CONDITIONS
MIN TYP MAX UNITS
PROG Pin Gain
Internal Sense Resistor Value
Measured at IIN = 1A (Note 3)
(Note 6)
52.7 µA/A
50 mΩ
Peak Inductor Current Limit
(Note 3)
l 5.50 6.5 9.00
A
Linear Inductor Current Limit
(Note 3)
l 4.00 5.0 6.85
A
N-Channel MOSFET Leakage
Switches B and C and E
0.1 5
µA
P-Channel MOSFET Leakage
Switches A and D
Switch F
0.1 5
0.1 10
µA
µA
N-Channel MOSFET On-Resistance
P-Channel MOSFET On-Resistance
Switch B
Switch C
Switch E (VOUT = 0V)
Switch A
Switch D
Switch F
70 mΩ
80 mΩ
95 mΩ
45 mΩ
40 mΩ
300 mΩ
MID Leakage Current
MID Pin Regulation
Active Charge Balancer Enable Threshold
Active Charge Balancer Hysteresis
VMID = 0V, VIN = 3.3V, VSW1 = 3.3V
VOUT = 4.8V
|VOUT/2-VMID|
l 2.304
0.1
2.400
60
60
10
2.496
118
µA
V
mV
mV
Active Charge Balancer Peak Current
(Note 3)
400 mA
Active Charge Balancer Valley Current
(Note 3)
50 mA
RUN Input High Threshold Voltage
l 1.2
V
RUN Input Low Threshold Voltage
l 0.3 V
RUN Input Current
RUN = 5.5V
0.01 1
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 LTC3128 is tested under pulsed load conditions such that TJ
TA. The LTC3128E is guaranteed to meet 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 LTC3128I is guaranteed
over the full –40°C to 125°C operating junction temperature range.
The junction temperature (TJ) is calculated from the ambient temperature
(TA) and power dissipation (PD) according to the formula: TJ = TA + (PD
θJA°C/W), where θJA is the package thermal impedance. 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 resistance and other environmental
factors.
Note 3. Current measurements are made when the output is not switching.
Note 4. This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may result in device degradation or failure.
Note 5. Failure to solder the exposed backside of the package to the PC
board ground plane will result in a thermal resistance much higher than
43°C/W in the QFN and 38°C/W in the TSSOP.
Note 6. Guaranteed by design. Not tested.
Note 7. Accuracy of this specification is directly related to the accuracy of
the resistor used to program the parameter.
3128f
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LTC3128
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted.
Efficiency vs VOUT (0.5A IIN)
100
90
80
70
60 VIN = 1.7V
VIN = 2.4V
50 VIN = 3.3V
VIN = 4.2V
40 VIN = 5.0V
0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5
VOUT (V)
3128 G01
Efficiency vs VOUT (3.0A IIN)
90
80
70
60
50
40
30
20
VIN = 2.4V
VIN = 3.3V
10 VIN = 4.2V
0 VIN = 5.0V
0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5
VOUT (V)
3128 G04
VROESURT v=s2C0hmaΩrg,eIITNim= e1,.0CAOUT = 1F,
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
VIN = 1.7V
VIN = 2.4V
VIN = 3.3V
0.5
0
VIN = 4.2V
VIN = 5.0V
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
TIME (s)
3128 G22
Efficiency vs VOUT (1.0A IIN)
100
90
80
70
60
50 VIN = 1.7V
VIN = 2.4V
40
VIN = 3.3V
VIN = 4.2V
30 VIN = 5.0V
0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5
VOUT (V)
3128 G02
Average Input Current Limit
vs Temperature (Normalized)
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
–45
–25 –5 15 35 55 75
TEMPERATURE (°C)
95 115
3128 G05
RVOESURT v=s2C0hmaΩrg,eIITNim= e2,.0CAOUT = 1F,
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0
VIN = 2.4V
VIN = 3.3V
VIN = 4.2V
VIN = 5.0V
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
TIME (s)
3128 G23
For more information www.linear.com/LTC3128
Efficiency vs VOUT (2.0A IIN)
100
90
80
70
60
50
40
30
20
VIN = 2.4V
VIN = 3.3V
10
0
VIN = 4.2V
VIN = 5.0V
0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5
VOUT (V)
3128 G03
VROESURT v=s2C0hmaΩrg,eIITNim= e0,.5CAOUT = 1F,
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
VIN = 1.7V
VIN = 2.4V
VIN = 3.3V
0.5
0
VIN = 4.2V
VIN = 5.0V
0 2 4 6 8 10 12 14 16 18 20 22 24
TIME (s)
3128 G21
VROESURT v=s2C0hmaΩrg,eIITNim= e3,.0CAOUT = 1F,
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0
VIN = 2.4V
VIN = 3.3V
VIN = 4.2V
VIN = 5.0V
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
TIME (s)
3128 G24
3128f
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