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PDF LTC3122 Data sheet ( Hoja de datos )
| Número de pieza | LTC3122 | |
| Descripción | 2.5A Synchronous Step-Up DC/DC Converter | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Features
n VIN Range: 1.8V to 5.5V, 500mV After Start-Up
n Output Voltage Range: 2.2V to 15V
n 800mA Output Current for VIN = 5V and VOUT = 12V
n Output Disconnects from Input When Shut Down
n Synchronous Rectification: Up to 95% Efficiency
n Inrush Current Limit
n Up to 3MHz Adjustable Switching Frequency
Synchronizable to External Clock
n Selectable Burst Mode® Operation: 25µA IQ
n Output Overvoltage Protection
n Soft-Start
n <1µA IQ in Shutdown
n 12-Lead, 3mm × 4mm × 0.75mm Thermally
Enhanced DFN and MSOP Packages
Applications
n RF Power
n Piezo Actuators
n Small DC Motors
n 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.
LTC3122
15V, 2.5A Synchronous
Step-Up DC/DC Converter
with Output Disconnect
Description
The LTC®3122 is a synchronous step-up DC/DC converter
with true output disconnect and inrush current limiting. The
2.5A current limit along with the ability to program output
voltages up to 15V makes the LTC3122 well suited for a
variety of demanding applications. Once started, opera-
tion will continue with inputs down to 500mV, extending
runtime in many applications.
The LTC3122 features output disconnect in shutdown,
dramatically reducing input power drain and enabling
VOUT to completely discharge. Adjustable PWM switching
from 100kHz to 3MHz optimizes applications for highest
efficiency or smallest solution footprint. The oscillator
can also be synchronized to an external clock for noise
sensitive applications. Selectable Burst Mode operation
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 ro-
bust protection under short-circuit, thermal overload, and
output overvoltage conditions. The LTC3122 is offered in
both a low profile 12-lead (3mm × 4mm × 0.75 mm) DFN
package and a 12-lead thermally enhanced MSOP package.
Typical Application
5V to 12V Synchronous Boost Converter with Output Disconnect
VIN
5V
4.7µF
3.3µH
OFF ON
SW
VIN VOUT
SD LTC3122
BURST PWM PWM/SYNC
CAP
RT FB
57.6k
VCC
SGND
VC
PGND
4.7µF
100nF
210k
390pF
VOUT
12V
800mA
1.02M
113k
22µF
10pF
3122 TA01a
For more information www.linear.com/LTC3122
Efficiency Curve
100 10
90 Burst Mode
80 OPERATION
70
60
PWM
1
50
40
30
0.1
PWM POWER LOSS
20
10
0
0.01
0.01
0.1 1 10 100 1000
LOAD CURRENT (mA)
3122 TA01b
3122fa
1
1 page  
Typical Performance Characteristics
PWM Mode Maximum Output
Current vs VIN
2.0
1.8
VOUT = 5V
VOUT = 7.5V
1.6 VOUT = 12V
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0.5 1.5 2.5 3.5 4.5 5.5
VIN (V)
3122 G10
Burst Mode Maximum Output
Current vs VIN
350
VOUT = 2.2V
300
VOUT = 5V
VOUT = 7.5V
250 VOUT = 12V
200
150
100
50
0
0.5 1.5 2.5 3.5 4.5 5.5
VIN, FALLING (V)
3122 G13
Peak Current Limit Change
vs Temperature
2
1
0
–1
–2
–3
–4
–50
–10 30
70 110 150
TEMPERATURE (°C)
3122 G11
Burst Mode No Load Input Current
vs VIN
10000
VOUT = 5V
VOUT = 7.5V
VOUT = 12V
1000
100
10
0.5
1.5 2.5 3.5 4.5 5.5
VIN, FALLING (V)
3122 G14
LTC3122
PWM Operation No Load Input
Current vs VIN
70
VOUT = 5V
60
VOUT = 7.5V
VOUT = 12V
50
40
30
20
10
0
0123456
VIN (V)
3122 G12
Burst Mode Quiescent Current
Change vs Temperature
75
60
45
30
15
0
–15
–50
–10 30
70 110 150
TEMPERATURE (°C)
3122 G14
SD Pin Threshold
VOUT
5V/DIV
900mV
VSD
500mV/DIV
400mV
1s/DIV
3122 G16
Frequency vs RT
3.0
2.5
FREQUENCY
PERIOD
12
10
2.0 8
1.5 6
1.0 4
0.5 2
00
0 100 200 300 400 500 600
RT (kΩ)
3122 G17
For more information www.linear.com/LTC3122
Frequency Accuracy
4 VOUT = 15V
3
VOUT = 3.6V
VOUT = 2.2V
2
1
0
–1
–2
–3
–4
01234
VIN FALLING (V)
56
3122 G18
3122fa
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5 Page 
LTC3122
Applications Information
Overvoltage Lockout
An overvoltage condition occurs when VOUT exceeds ap-
proximately 16.2V. Switching is disabled and the internal
soft-start ramp is reset. Once VOUT drops below approxi-
mately 15.6V, a soft-start cycle is initiated and switching
is enabled. If the boost converter output is lightly loaded
so that the time constant product of the output capaci-
tance, COUT, and the output load resistance, ROUT is near
or greater than the soft-start time of approximately 10ms,
the soft-start ramp may end before or soon after switching
resumes, defeating the inrush current limiting of the closed
loop soft-start following an overvoltage event.
Short-Circuit Protection
The LTC3122 output disconnect feature allows output
short-circuit protection. To reduce power dissipation under
overload and short-circuit conditions, the peak switch
current limit is reduced to 1.6A. Once VOUT > 1.5V, the
current limit is set to its nominal value of 3.5A.
VIN > VOUT Operation
The LTC3122 step-up converter will maintain voltage regu-
lation even when the input voltage is above the desired
output voltage. Note that operating in this mode will exhibit
lower efficiency and a reduced output current capability.
Refer to the Typical Performance Characteristics section
for details.
Burst Mode Operation
When the PWM/SYNC pin is held low, the boost converter
operates in Burst Mode operation to improve efficiency
at light loads and reduce standby current at no load. The
input thresholds for this pin are determined relative to VCC
with a low being less than 10% of VCC and a high being
greater than 90% of VCC. The LTC3122 will operate in
fixed frequency PWM mode even if Burst Mode operation
is commanded during soft-start.
In Burst Mode operation, the LTC3122 switches asynchro-
nously. The inductor current is first charged to 600mA
by turning on the N-channel MOSFET switch. Once this
current threshold is reached, the N-channel is turned off
and the P-channel synchronous switch is turned on, de-
livering current to the output. When the inductor current
discharges to approximately zero, the cycle repeats. In
Burst Mode operation, energy is delivered to the output
until the nominal regulation value is reached, at which
point the LTC3122 transitions to sleep mode. In sleep, the
output switches are turned off and the LTC3122 consumes
only 25μA of quiescent current. When the output volt-
age droops approximately 1%, switching resumes. This
maximizes efficiency at very light loads by minimizing
switching and quiescent losses. Output voltage ripple in
Burst Mode operation is typically 1% to 2% peak-to-peak.
Additional output capacitance (10μF or greater), or the
addition of a small feed-forward capacitor (10pF to 50pF)
connected between VOUT and FB can help further reduce
the output ripple.
The maximum output current (IOUT) capability in Burst
Mode operation varies with VIN and VOUT, as shown in
Figure 2.
350 VOUT = 2.2V
300
VOUT = 5V
VOUT = 7.5V
250 VOUT = 12V
200
150
100
50
0
0.5 1.5 2.5 3.5 4.5 5.5
VIN, FALLING (V)
3122 F02
Figure 2. Burst Mode Maximum Output Current vs VIN
For more information www.linear.com/LTC3122
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11 Page | ||
| Páginas | Total 26 Páginas | |
| PDF Descargar | [ Datasheet LTC3122.PDF ] | |
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