reduces quiescent current to 25µA, ensuring high efficiency
across the entire load range. An internal soft-start limits
inrush current during start-up.
Other features include a <1µA shutdown current and robust
protection under short-circuit, thermal overload, and output
overvoltage conditions. The LTC3121 is offered in a low
profile 12-lead (3mm × 4mm × 0.75mm) DFN package.
n
n
n
n
n
V
IN
Range: 1.8V to 5.5V, 500mV After Start-Up
Output Voltage Range: 2.2V to 15V
400mA Output Current for V
IN
= 5V and V
OUT
= 12V
Output Disconnects from Input When Shut Down
Synchronous Rectification: Up to 95% Efficiency
Inrush Current Limit
Up to 3MHz Adjustable Switching Frequency
Synchronizable to External Clock
Selectable Burst Mode
®
Operation: 25µA I
Q
Output Overvoltage Protection
Soft-Start
<1µA I
Q
in Shutdown
12-Lead, 3mm × 4mm Thermally Enhanced DFN
Package
applicaTions
n
n
n
n
PCI Express Cards/Systems
Piezo Actuators
Small DC Motors
12V Analog Rail From Battery, 5V, or Backup Capacitor
L,
LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
Typical applicaTion
5V to 12V Synchronous Boost Converter with Output Disconnect
V
IN
5V
6.8µH
SW
V
IN
4.7µF
OFF ON
BURST PWM
SD
LTC3121
V
OUT
100nF
CAP
FB
V
C
SGND
4.7µF
PGND
210k
390pF
10pF
113k
1.02M
22µF
100
90
V
OUT
12V
400mA
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.01
0.1
10
1
LOAD CURRENT (mA)
100
0.01
600
PWM POWER LOSS
0.1
Burst Mode
OPERATION
PWM
1
POWER LOSS (W)
Efficiency Curve
10
PWM/SYNC
RT
V
CC
57.6k
3121 TA01b
3121 TA01a
3121f
For more information
www.linear.com/LTC3121
1
LTC3121
absoluTe MaxiMuM raTings
(Note 1)
pin conFiguraTion
TOP VIEW
SW
PGND
V
IN
PWM/SYNC
V
CC
RT
1
2
3
4
5
6
13
PGND
12 CAP
11 V
OUT
10 SGND
9
8
7
SD
FB
V
C
V
IN
Voltage .................................................. –0.3V to 6V
V
OUT
Voltage ............................................ –0.3V to 18V
SW Voltage (Note 2) .................................. –0.3V to 18V
SW Voltage (Pulsed < 100ns) (Note 2)....... –0.3V to 19V
V
C
, RT Voltage .......................................... –0.3V to V
CC
CAP Voltage
V
OUT
< 5.7V ............................–0.3V to (V
OUT
+ 0.3V)
5.7V ≤ V
OUT
≤ 11.7V...... (V
OUT
– 6V) to (V
OUT
+ 0.3V)
V
OUT
> 11.7V .................................(V
OUT
– 6V) to 12V
All Other Pins ............................................... –0.3V to 6V
Operating Junction Temperature Range
(Notes 3, 4) ............................................ –40°C to 125°C
Storage Temperature Range .................. –65°C to 150°C
DE PACKAGE
12-LEAD (4mm
×
3mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 43°C/W (NOTE 5),
θ
JC
= 5°C/W
EXPOSED PAD (PIN 13) IS PGND,
MUST BE SOLDERED TO PCB FOR RATED THERMAL PERFORMANCE
orDer inForMaTion
LEAD FREE FINISH
LTC3121EDE#PBF
LTC3121IDE#PBF
TAPE AND REEL
LTC3121EDE#TRPBF
LTC3121IDE#TRPBF
PART MARKING*
3121
3121
PACKAGE DESCRIPTION
12-Lead (4mm × 3mm) Plastic DFN
12-Lead (4mm × 3mm) Plastic DFN
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.
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/
3121f
2
For more information
www.linear.com/LTC3121
LTC3121
elecTrical characTerisTics
PARAMETER
Minimum Start-Up Voltage
Input Voltage Range
Output Voltage Adjust Range
Feedback Voltage
Feedback Input Current
Quiescent Current, Shutdown
Quiescent Current, Active
Quiescent Current, Burst
N-channel MOSFET Switch Leakage Current
P-channel MOSFET Switch Leakage Current
N-channel MOSFET Switch On-Resistance
P-channel MOSFET Switch On-Resistance
N-channel MOSFET Current Limit
Maximum Duty Cycle
Minimum Duty Cycle
Switching Frequency
SYNC Frequency Range
PWM/SYNC Input High
PWM/SYNC Input Low
PWM/SYNC Input Current
CAP Clamp Voltage
Error Amplifier Transconductance
Error Amplifier Output Current
Soft-Start Time
SD
Input High
SD
Input Low
SD
Input Current
V
SD
= 5.5V
l
l
The
l
denotes the specifications which apply over the full operating junction
temperature range, otherwise specifications are at T
A
= 25°C (Note 3). V
IN
= 3.6V, V
OUT
= 12V, RT = 57.6k unless otherwise noted.
CONDITIONS
V
OUT
= 0V
After V
OUT
≥ 2.2V
l
l
l
l
MIN.
0.5
2.2
1.178
TYP
1.7
MAX
1.8
5.5
15
UNITS
V
V
V
V
nA
µA
µA
µA
µA
µA
µA
Ω
Ω
1.202
1
0.01
500
25
10
1.225
50
1
700
40
20
30
70
V
FB
= 1.4V
V
SD
= 0V, V
OUT
= 0V, Not Including Switch Leakage
V
C
= 0V, Measured On V
IN
, Non-Switching
Measured on V
IN
, V
FB
> 1.4V
Measured on V
OUT
, V
FB
> 1.4V
V
SW
= 15V, V
OUT
= 15V, V
C
= 0V
V
SW
= 0V, V
OUT
= 15V, V
SD
= 0V
l
l
0.1
0.1
0.121
0.188
V
IN
= 3.3V
V
FB
= 1.0V
V
FB
= 1.4V
l
l
l
l
l
l
l
1.5
90
0.85
0.1
0.9 •V
CC
1.8
94
2.7
0
A
%
%
MHz
MHz
V
V
µA
V
µS
µA
ms
V
1
1.15
3
0.1•V
CC
V
PWM/SYNC
= 5.5V
V
OUT
> 6.1V, Referenced to V
OUT
l
0.01
–5.2
70
–5.6
100
±25
10
1.6
1
–6.0
130
0.25
1
2
V
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:
Voltage transients on the SW pin beyond the DC limit specified in
the Absolute Maximum Ratings are non-disruptive to normal operations
when using good layout practices, as shown on the demo board or
described in the data sheet or application notes.
Note 3:
The LTC3121 is tested under pulsed load conditions such that
T
A
≈ T
J
. The LTC3121E is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 125°C operating
junction temperature range are assured by design, characterization and
correlation with statistical process controls. The LTC3121I is guaranteed
to meet specifications over the full –40°C to 125°C operating junction
temperature range. The junction temperature (T
J
in °C) is calculated from
the ambient temperature (T
A
in °C) and power dissipation (P
D
in watts)
according to the formula: T
J
= T
A
+ (P
D
•
θ
JA
) where
θ
JA
is the thermal
impedance of the package.
Note 4:
The LTC3121 includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature shutdown 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 impedance much higher than
the rated package specifications.
3121f
For more information
www.linear.com/LTC3121
3
LTC3121
Configured as front page application unless otherwise specified.
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