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PDF LTC3626 Data sheet ( Hoja de datos )
| Número de pieza | LTC3626 | |
| Descripción | 2.5A Synchronous Monolithic Step-Down Regulator | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC3626
20V, 2.5A Synchronous
Monolithic Step-Down Regulator with
Current and Temperature Monitoring
FEATURES
DESCRIPTION
n 3.6V to 20V Input Voltage Range
n Wide Output Voltage Range of 0.6V to 97% VIN
Optimized for 0.6V to 6V
n Low RDS(ON) Integrated Switches Provide Up to 95%
Efficiency
n Up to 2.5A of Output Current
n Average Input and Output Current Monitoring
n Programmable Average Input/Output Current Limit
n Die Temperature Monitor and Programmable Limit
n Adjustable Switching Frequency: 500kHz to 3MHz
n External Frequency Synchronization
n Current Mode Operation for Excellent Line and Load
Transient Response
n 0.6V Reference with 1% Accuracy Over Temperature
n User Selectable Burst Mode® or Forced Continuous
Operation
n Short-Circuit Protected
n Output Voltage Tracking Capability
n Power Good Status Output
n Available in Small, Thermally Enhanced, 20-Lead
(3mm × 4mm) QFN Package
APPLICATIONS
n Distributed Power Systems
n Battery-Powered Instruments
n Point-of-Load Power Supply
The LTC®3626 is a high efficiency, monolithic synchronous
buck regulator using a phase-lockable controlled on-time,
current mode architecture capable of supplying up to 2.5A
of output current. The operating supply voltage range is
3.6V to 20V, making it suitable for a wide range of power
supply applications.
The operating frequency is programmable from 500kHz to
3MHz with an external resistor allowing the use of small
surface mount inductors. For applications sensitive to
switching noise, the LTC3626 can be externally synchro-
nized over the same frequency range. An internal phase-
locked loop aligns the on-time of the top power MOSFET to
the internal or external clock. This unique controlled on-time
architecture is ideal for high step-down ratio applications
that demand high switching frequencies and fast transient
response. An internal phase lock loop servos the on-time
of the internal one-shot timer to match the frequency of
the internal clock or an applied external clock.
The LTC3626 offers two operational modes: Burst
Mode and forced continuous mode to allow the user
to optimize output voltage ripple, noise and light load
efficiency for a given application.
L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered and Hot
Swap is a trademark of Linear Technology Corporation. All other trademarks are the property
of their respective owners. Protected by U.S. Patents, including 5481178, 5847554, 6580258,
6304066, 6476589, 6774611, 5994885.
TYPICAL APPLICATION
VIN
3.6V TO 20V
47µF
PVIN
SVIN
RUN BOOST
LTC3626
PGOOD
2.2µF
INTVCC
TRACK/SS
ITH
SW
MODE/SYNC
TSET
VON
IMONIN
TMON
FB
RT
IMONOUT
1µF 5.1k SGND PGND
0.1µF
2.2µH
324k
115k
22pF
25.5k
3626 TA01
VOUT
3.3V
47µF 2.5A
Efficiency vs Load Current
100
90
VOUT = 3.3V
80 10
70
60 1
50
40 0.1
30
20
10
0
1
Burst Mode
OPERATION
0.01
VIN = 12V
VIN = 5V 0.001
10 100 1000 10000
LOAD CURRENT (mA)
3626 TA01b
3626f
1
http://www.Datasheet4U.com
1 page  
LTC3626
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, PVIN = SVIN = 12V, f = 1MHz unless otherwise noted.
Efficiency vs Load Current
(Burst Mode Operation)
100
90
VOUT = 1.8V
80
70
60
50
40
30
20
VIN = 4V
VIN = 8V
10 VIN = 12V
0 VIN = 20V
1 10 100 1000 10000
LOAD CURRENT (mA)
3626 G01
Efficiency vs Load Current (Forced
Continuous Mode Operation)
100
90
VOUT = 1.8V
80
70
60
50
40
30
20
VIN = 4V
VIN = 8V
10 VIN = 12V
0 VIN = 20V
1 10 100 1000 10000
LOAD CURRENT (mA)
3626 G02
Efficiency vs Load Current
(Burst and Forced Continuous)
100 Burst Mode OPERATION
90
80
70
60
FORCED
CONTINUOUS
50 MODE OPERATION
40
30
20
10
0
VOUT = 5V
VOUT = 3.3V
1 10 100 1000 10000
LOAD CURRENT (mA)
3626 G02
Efficiency vs Input Voltage
(Burst Mode Operation)
100
VOUT = 1.8V
95
90
85
80
75
70 ILOAD = 1A
65
ILOAD = 2.5A
ILOAD = 100mA
ILOAD = 10mA
60
4 6 8 10 12 14 16 18 20 22
INPUT VOLTAGE (V)
3626 G04
Efficiency vs Frequency (Forced
Continuous Mode Operation)
100
90
VOUT = 3.3V
80
70
60
50
40
30
20
f = 500kHz
f = 1MHz
10
f = 2MHz
f = 3MHz
0
1 10 100 1000 10000
LOAD CURRENT (mA)
3626 G05
Reference Voltage
vs Temperature
0.606
0.604
0.602
0.600
0.598
0.596
0.594
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3626 G06
Internal MOSFET
vs Temperature
RDS(ON)
160
140
TOP SWITCH
120
100
80
BOTTOM SWITCH
60
40
20
0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3626 G07
Temperature Monitor
vs Temperature
125
2.0
100 1.9
75 1.7
50 1.6
25 1.5
0 1.4
–25 1.2
–50
–50 –25
0 25 50 75
TEMPERATURE (°C)
1.1
100 125
3626 G08
3626f
5
5 Page 
LTC3626
OPERATION
The LTC3626 is a current mode, monolithic, step-down
regulator capable of providing up to 2.5A of output current
from an input supply as high as 20V. Its unique controlled
on-time architecture allows extremely low step-down ratios
while maintaining a constant switching frequency. The part
is enabled by raising the RUN pin above 1.25V (typical).
Main Control Loop
In normal operation the internal top power MOSFET is
turned on for a fixed interval determined by an internal
one-shot timer (“ON” signal in the Functional Diagram).
When the top power MOSFET turns off, the bottom power
MOSFET turns on until the current comparator, ICMP, trips,
thus restarting the one-shot timer and initiating the next
cycle. The inductor current is monitored by sensing the
voltage drop across the bottom power MOSFET. The volt-
age at the ITH node sets the ICMP comparator threshold
corresponding to the inductor valley current. The error
amplifier, EA, adjusts the ITH voltage by comparing an
internal 0.6V reference voltage to the feedback signal, VFB,
derived from the output voltage. If, for example, the load
current increases, the output voltage will decrease relative
to the 0.6V reference. The ITH voltage then rises until the
average inductor current matches that of the load current.
At light load currents the inductor current can drop to
zero or become negative. If the LTC3626 is configured for
Burst Mode operation, this inductor current condition is
detected by the current reversal comparator, IREV, which
in turn shuts off the bottom power MOSFET and places
the part into a low quiescent current sleep state resulting
in discontinuous operation and increased efficiency at low
load currents. Both power MOSFETs remain off with the
part in sleep and the output capacitor supplying the load
current until the ITH voltage rises sufficiently to initiate
another cycle. Discontinuous operation is disabled by
tying the MODE/SYNC pin to ground, placing the LTC3626
into forced continuous mode. In forced continuous mode,
continuous synchronous operation occurs regardless of
the output load current.
The operating frequency is determined by the valueof the RT
resistor, which programs the current for the internal oscil-
lator. An internal phase-locked loop adjusts the switching
regulator on-time to track the internal oscillator edge and
force a constant switching frequency, subject to tON and
tOFF time constraints as shown in the Electrical Character-
istics table. Alternatively, the RT pin can be connected to
the INTVCC pin which causes the internal oscillator to run
at the default frequency of 2MHz. Finally, a clock signal
can be applied to the MODE/SYNC pin to synchronize the
switching frequency to an external source. The regulator
defaults to forced continuous operation when an external
clock signal is applied.
Output/Input Current Monitor and Limit
The LTC3626 provides a scaled replica of the average
output current and a scaled replica of the average input
current at the IMONOUT and IMONIN pins respectively. The
average current at each of these pins will be 1/16,000th
of the measured average current. Further, the voltage at
each pin is continuously fed to independent current limit
amplifiers that have a voltage reference at 1.2V. Thus, a
programmable average current limit for the output current
and/or input current may be obtained by placing a resistor
of suitable value at the pin of interest so as to produce
1.2V at the desired current limit. When the current limit
feature is used, a compensation capacitor (1µF typical)
should be placed in parallel with the chosen resistor. The
output or input current monitor and limit circuits may be
individually disabled by pulling IMONOUT or IMONIN to
INTVCC as appropriate.
3626f
11
11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet LTC3626.PDF ] | |
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