LINEAR TECHNOLOGY LTC3125 Technical data
LTC3125
1.2A Synchronous Step-Up
DC/DC Converter with
Input Current Limit
FEATURES
n
Programmable Average Input Current Limit
n
5% Input Current Accuracy
n
200mA to 1000mA Program Range
n
VIN: 1.8V to 5.5V, V
n
Supports High Current GSM/GPRS Load Burst
n
VIN > V
n
1.6MHz Fixed Frequency Operation
n
Internal Current Sense Resistor
n
1.2A Peak Current Limit
n
Up to 93% Effi ciency
n
Output Disconnect in Shutdown
n
Soft-Start
n
Low Quiescent Current Burst Mode® Operation (15µA)
n
Available in 2mm × 3mm × 0.75mm DFN Package
Operation
OUT
: 2V to 5.25V
OUT
APPLICATIONS
n
GSM/GPRS PCMCIA/CompactFlash PC Card Modems
n
Wireless Emergency Locators
n
Portable Radios
n
Supercap Chargers
DESCRIPTION
The LTC®3125 is a high effi ciency, synchronous step-up
DC/DC converter with an accurate programmable average
input current limit. The ±5% accurate average input current
is resistor programmable and suitable for a wide variety of
applications. In mobile computing, GSM and GPRS cards
demand high current pulses well beyond the capability
of the PC Card and CompactFlash slots. The LTC3125 in
concert with a reservoir capacitor, keeps the slot power
safely within its capabilities providing a high performance
and simple solution.
Synchronous rectifi cation produces high effi ciency while
the 1.6MHz switching frequency minimizes the solution
footprint. The current mode PWM design is internally compensated. Output disconnect allows the load to discharge in
shutdown, while also providing inrush current limiting.
Other features include a <1µA shutdown current, shortcircuit and thermal overload protection. The LTC3125 is offered in a low profi le 0.75mm × 2mm × 3mm package.
L, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
PCMCIA/CompactFlash (3.3V/500mA Max),
4V GSM Pulsed Load
2.2µH
LTC3125
GND
SW
V
OUT
FB
V
3.3V
500mA
IN
10µF
CER
OFF ON
44.2k
CS
V
IN
SHDN
PROG
1.24M
536k
V
OUT
4V
2A PULSED LOAD
2200µF
s2
TANT
3125 TA01a
Effi ciency vs Load Current
100
90
80
70
60
50
40
EFFICIENCY (%)
30
20
10
0
0.001
V
= 4V
OUT
= 3.3V
V
IN
= 2.4V
V
IN
0.01 0.1 1
LOAD CURRENT (A)
3125 TA01b
1
POWER LOSS (W)
0.1
0.01
0.001
3125f
1
LTC3125
PIN CONFIGURATION ABSOLUTE MAXIMUM RATINGS
(Note 1)
VIN, V
Voltage ......................................... –0.3V to 6V
OUT
SW Voltage .................................................. –0.3V to 6V
SW Voltage < 100ns .................................... –0.3V to 7V
All Other Pins ............................................... –0.3V to 6V
Operating Temperature Range
(Notes 2, 5) .............................................. –40°C to 85°C
Junction Temperature ........................................... 125°C
Storage Temperature Range ................... –65°C to 125°C
GND
FB
PROG
V
IN
8-LEAD (2mm s 3mm) PLASTIC DFN
T
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
JMAX
TOP VIEW
1
2
3
4
= 125°C, θJA = 64°C/W (NOTE 6)
9
DCB PACKAGE
8
7
6
5
SW
V
OUT
SHDN
CS
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC3125EDCB#PBF LTC3125EDCB#TRPBF LDGY
Consult LTC Marketing for parts specifi ed with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based fi nish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifi cations, go to: http://www.linear.com/tapeandreel/
8-Lead (2mm × 3mm) Plastic DFN
–40°C to 85°C
ELECTRICAL CHARACTERISTICS
The l denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at TA = 25°C. VIN = 3.3V, V
PARAMETER CONDITIONS MIN TYP MAX UNITS
Input Voltage Range 1.8 5.5 V
Minimum Start-Up Voltage
Output Voltage Adjust Range
Feedback Voltage
Feedback Input Current 150 nA
Quiescent Current—Shutdown V
Quiescent Current —Active Measured on V
Quiescent Current—Burst Measured on V
N-Channel MOSFET Switch Leakage V
P-Channel MOSFET Switch Leakage V
N-Channel MOSFET Switch On-Resistance V
P-Channel MOSFET Switch On-Resistance V
N-Channel MOSFET Current Limit
Current Limit Delay to Output (Note 3) 60 ns
Average Input Current Limit R
= 0V, Not Including Switch Leakage, V
SHDN
, Nonswitching 300 500 µA
OUT
, FB = 1.230V 15 25 µA
OUT
= 5V, VIN = 5V 0.1 10 µA
SW
= 5V, V
SW
= 3.3V 0.125
OUT
= 3.3V 0.200
OUT
PROG
R
PROG
= 0V, VIN = 5V 0.1 20 µA
OUT
= 44.2k
= 44.2k, –40°C to 85°C
= 4.5V unless otherwise noted.
OUT
l
l
l
1.176 1.200 1.229 V
= 0V 0.01 1 µA
OUT
l
1.2 1.8 A
475
l
465
1.6 1.8 V
2 5.25 V
500
500
525
535
mA
mA
2
3125f
LTC3125
ELECTRICAL CHARACTERISTICS
The l denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at T
PARAMETER CONDITIONS MIN TYP MAX UNITS
PROG Current Gain (Note 3) 22.1 k-A/A
Maximum Duty Cycle V
Minimum Duty Cycle V
Frequency
SHDN Input High 1V
SHDN Input Low 0.35 V
SHDN Input Current V
FB
FB
SHDN
= 25°C. VIN = 3.3V, V
A
= 1.15V
= 1.3V
= 4.5V unless otherwise noted.
OUT
l
l
l
85 92 %
0%
1.3 1.6 1.9 MHz
= 1.2V 0.3 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 LTC3125 is guaranteed to meet performance specifi cations
from 0°C to 85°C. Specifi cations over –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3: Specifi cation is guaranteed by design and not 100% tested in
Note 4: Current measurements are made when the output is not switching.
Note 5: 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 specifi ed maximum operating junction
temperature may result in device degradation or failure.
Note 6: Failure to solder the exposed backside of the package to the PC
board ground plane will result in a thermal resistance much higher than
60°C/W.
production.
TYPICAL PERFORMANCE CHARACTERISTICS
Effi ciency vs Load Current,
V
= 2.5V
OUT
100
90
80
70
60
50
40
EFFICIENCY (%)
30
20
10
0
0.001
VIN = 2.1V
V
IN
0.01 0.1 1
LOAD CURRENT (A)
= 1.8V
3125 G01
1
0.1
POWER LOSS (W)
0.01
0.001
0.0001
100
90
80
70
60
50
40
EFFICIENCY (%)
30
20
10
0
0.001
(TA = 25°C unless otherwise noted)
Effi ciency vs Load Current,
V
= 3.3V
OUT
VIN = 2.8V
= 2.4V
V
IN
= 2V
V
IN
0.01 0.1 1
LOAD CURRENT (A)
3125 G02
1
POWER LOSS (W)
0.1
0.01
0.001
3125f
3
LTC3125
TYPICAL PERFORMANCE CHARACTERISTICS
Effi ciency vs Load Current,
V
= 5V
OUT
100
90
80
70
60
50
40
EFFICIENCY (%)
30
20
10
0
0.001
0.01 0.1 1
LOAD CURRENT (A)
VIN = 4V
V
Average Input Current Limit vs
Temperature
1.50
NORMALIZED TO 25°C
1.00
0.50
0
–0.50
–1.00
AVERAGE INPUT CURRENT LIMIT CHANGE (%)
–1.50
–50
02550
–25
TEMPERATURE (°C)
= 3.3V
IN
3125 G03
75 100
3125 G06
1
POWER LOSS (W)
0.1
0.01
0.001
No-Load Input Current vs V
4.0
3.5
3.0
2.5
2.0
(mA)
IN
I
1.5
1.0
0.5
0
1.5
V
= 4V
OUT
V
= 3.8V
OUT
V
= 3.3V
OUT
V
= 2.5V
OUT
2 2.5 3.5
VIN (V)
Average Input Current vs R
1.25
1.00
0.75
0.50
0.25
AVERAGE INPUT CURRENT LIMIT (A)
0
10 20 30 40 50 70 80 90 100
60 110
R
(k)
PROG
3
(TA = 25°C unless otherwise noted)
IN
4
3125 G04
PROG
3125 G07
Average Input Current Limit vs V
2.0
NORMALIZED TO 25°C
1.5
1.0
0.5
0
–0.5
–1.0
–1.5
AVERAGE INPUT CURRENT LIMIT CHANGE (%)
–2.0
2.0 2.5 3.5
1.5
Peak Current Limit vs V
2.55
V
= 3.8V
OUT
2.50
2.45
2.40
2.35
2.30
2.25
2.20
INPUT CURRENT (A)
2.15
2.10
2.05
2.00
1.5
R
PROG
= 0
2 2.5
3
3.0
VIN (V)
3.5
VIN (V)
IN
4.5
4.0
3125 G05
IN
4
4.5
5
3125 G08
5.5
Burst Mode Threshold Current
vs V
IN
50
V
= 3.3V
OUT
= 1500µF
C
OUT
L = 2.2µH
40
30
LOAD CURRENT (mA)
20
10
1.8
2.0
2.2
VIN (V)
4
2.4
2.6
3125 G09
2.8
Burst Mode Threshold Current
vs V
IN
50
V
= 2.5V
OUT
= 1500µF
C
OUT
45
L = 2.2µH
40
35
30
LOAD CURRENT (mA)
25
20
1.8
1.9 2.0 2.1 2.2
VIN (V)
3125 G10
Oscillator Frequency vs V
2
NORMALIZED TO V
1
0
–1
–2
–3
–4
–5
FREQUENCY CHANGE (%)
–6
–7
–8
2.5
2.0
3.0
OUT
V
OUT
3.5
= 3.3V
(V)
4.0
OUT
4.5
5.0
3125 G11
3125f
LTC3125
TYPICAL PERFORMANCE CHARACTERISTICS
R
R
vs V
DS(ON)
0.450
0.400
0.350
0.300
0.250
RDS(ON) ()
0.200
0.150
0.100
0.050
2 2.5 3.5
1.5
Feedback vs Temperature
0.50
NORMALIZED TO 25°C
0.25
OUT
PMOS
NMOS
V
3
OUT
(V)
4 4.5 5
3125 G12
240
220
200
180
(m)
160
DS(ON)
R
140
120
100
0.50
0.25
–50
vs Temperature
DS(ON)
V
= 4V
OUT
PMOS
NMOS
30 70 90
–30 –10
Current Sense Voltage (V
10 50
TEMPERATURE (°C)
RPROG
vs Temperature Burst Mode Current vs V
NORMALIZED TO 25°C
(TA = 25°C unless otherwise noted)
Oscillator Frequency
vs Temperature
10
NORMALIZED TO 25°C
8
6
4
2
0
–2
–4
FREQUENCY CHANGE (%)
–6
–8
–10
–50
–25
3125 G13
25 50
0
TEMPERATURE (°C)
)
16.0
15.5
OUT
75
100
3125 G14
0
(%)
FB
–0.25
–0.50
CHANGE IN V
–0.75
–1.00
–50
–30 –10
2V/DIV
SHDN
5V/DIV
INPUT
CURRENT
200mA/DIV
30 70 90
10 50
TEMPERATURE (°C)
V
and IIN During Soft-Start
OUT
V
OUT
= 3.3V
IN
= 4.5V
V
OUT
= 4.4mF
C
OUT
L = 2.7µH
0
(%)
FB
–0.25
–0.50
CHANGE IN V
–0.75
3125 G15
–1.00
–50
–30 –10
TEMPERATURE (°C)
30 70 90
10 50
3125 G15
V
V
OUT
2V/DIV
SHDN
5V/DIV
BURST
CURRENT
20ms/DIVV
3125 G18
INPUT
CURRENT
200mA/DIV
IN
V
OUT
C
OUT
L = 2.7µH
15.0
14.5
(µA)
Q
I
14.0
13.5
13.0
1.5
2 2.5
and IIN During Soft-Start
OUT
= 3.3V
= 4.5V
= 0.47F
1s/DIVV
3.5 4.5 5
34
V
(V)
OUT
3125 G19
3125 G17
3125f
5
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