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PDF LT8613 Data sheet ( Hoja de datos )
| Número de pieza | LT8613 | |
| Descripción | 6A Synchronous Step-Down Regulator | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Features
n Rail-to-Rail Current Sense Amplifier with Monitor
n Wide Input Voltage Range: 3.4V to 42V
n Ultralow Quiescent Current Burst Mode® Operation:
3μA IQ Regulating 12VIN to 3.3VOUT
Output Ripple < 10mVP-P
n High Efficiency Synchronous Operation:
95% Efficiency at 3A, 5VOUT from 12VIN
94% Efficiency at 3A, 3.3VOUT from 12VIN
n Fast Minimum Switch-On Time: 40ns
n Low Dropout Under All Conditions: 250mV at 3A
n Allows Use Of Small Inductors
n Low EMI
n Adjustable and Synchronizable: 200kHz to 2.2MHz
n Current Mode Operation
n Accurate 1V Enable Pin Threshold
n Internal Compensation
n Output Soft-Start and Tracking
n Small Thermally Enhanced 3mm × 6mm 28-Lead
QFN Package
Applications
n Automotive and Industrial Supplies
n General Purpose Step-Down
n CCCV Power Supplies
LT8613
42V, 6A Synchronous
Step-Down Regulator with
Current Sense and 3µA
Quiescent Current
Description
The LT®8613 is a compact, high efficiency, high speed
synchronous monolithic step-down switching regulator
that consumes only 3µA of quiescent current. Top and
bottom power switches are included with all necessary
circuitry to minimize the need for external components.
The built-in current sense amplifier with monitor and
control pins allows accurate input or output current
regulation and limiting. Low ripple Burst Mode operation
enables high efficiency down to very low output currents
while keeping the output ripple below 10mVP-P. A SYNC
pin allows synchronization to an external clock. Internal
compensation with peak current mode topology allows
the use of small inductors and results in fast transient
response and good loop stability. The EN/UV pin has an
accurate 1V threshold and can be used to program VIN
undervoltage lockout or to shut down the LT8613 reduc-
ing the input supply current to 1µA. A capacitor on the
TR/SS pin programs the output voltage ramp rate during
start-up. The PG flag signals when VOUT is within ±9% of
the programmed output voltage as well as fault conditions.
The LT8613 is available in a small 28-lead 3mm × 6mm
QFN package with exposed pad for low thermal resistance.
L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
Typical Application
5V Step-Down Converter with 6A Output Current Limit
VIN
5.8V TO 42V
10µF ON OFF
VIN
EN/UV
BST
SYNC
LT8613
IMON
SW
ICTRL
ISP
ISN
BIAS
INTVCC
PG
TR/SS
10µF RT
FB
1µF 60.4k PGND GND
0.1µF
3.9µH
8mΩ
1µF
VOUT
5V
6A
10pF
1M
243k
100µF
fSW = 700kHz
L: EPCOS B82559
8613 TA01a
Efficiency at 5VOUT
100 VIN = 12V
95
90 VIN = 24V
85
80
75
70
65 fSW = 700kHz
L = 3.9µH
60
01 2 3 4
LOAD CURRENT (A)
56
8613 TA01b
For more information www.linear.com/LT8613
8613f
1
1 page  
Typical Performance Characteristics
LT8613
No Load Supply Current
3.8
3.6
3.4
3.2
3.0
2.8
2.6
2.4
2.2
2.0 VOUT = 5V
0 10
20
30
INPUT VOLTAGE (V)
40
50
8613 G10
Minimum On-Time
45
40
35
VSYNC = 0V
30
25 VSYNC = 3.3V
20
15
0
12345
LOAD CURRENT (A)
6
8613 G13
Switching Frequency
740 RT = 60.4k
730
720
710
700
690
680
670
660
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
8613 G16
Top FET Current Limit vs Duty Cycle
10
9
8
7
6
5
4
0 20 40 60 80 100
DUTY CYCLE (%)
8613 G11
Minimum Off-Time
100
95
90
85
80
75
70
65
60
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
8613 G14
Burst Frequency
800 VIN = 12V
700
VOUT = 5V
L = 3.9µH
600
500
400
300
200
100
0
0 100 200 300 400 500
LOAD CURRENT (mA)
8613 G17
For more information www.linear.com/LT8613
Top FET Current Limit
11
10 15% DUTY CYCLE
9
8
7 70% DUTY CYCLE
6
5
4
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
8613 G12
Dropout Voltage
0.6
0.5
0.4
0.3
0.2
0.1
0
0 1 23 4 56
LOAD CURRENT (A)
8613 G15
Minimum Load to Full Frequency
(SYNC Hi)
60
50
40
30
20
10
0
0 10 20 30 40 50
INPUT VOLTAGE (V)
8613 G18
8613f
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5 Page 
LT8613
Operation
The LT8613 is a monolithic, constant frequency, current
mode step-down DC/DC converter. An oscillator, with
frequency set using a resistor on the RT pin, turns on
the internal top power switch at the beginning of each
clock cycle. Current in the inductor then increases until
the top switch current comparator trips and turns off the
top power switch. The peak inductor current at which the
top switch turns off is controlled by the voltage on the
internal VC node. The error amplifier servos the VC node
by comparing the voltage on the VFB pin with an internal
0.97V reference. When the load current increases it causes
a reduction in the feedback voltage relative to the reference
leading the error amplifier to raise the VC voltage until the
average inductor current matches the new load current.
When the top power switch turns off, the synchronous
power switch turns on until the next clock cycle begins or
inductor current falls to zero. If overload conditions result
in more than 10A flowing through the bottom switch (valley
current), the next clock cycle will be delayed until switch
current returns to a safe level.
The LT8613 includes a current control and monitoring
loop using the ISN, ISP, IMON and ICTRL pins. The ISP/
ISN pins monitor the voltage across an external sense
resistor such that the VISP-VISN does not exceed 50mV
by limiting the peak inductor current controlled by the VC
node. The current sense amplifier inputs (ISP/ISN) are rail-
to-rail such that input, output, or other system currents
may be monitored and regulated. The IMON pin outputs
a ground-referenced voltage equal to 20 times the voltage
between the ISP-ISN pins for monitoring system currents.
The ICTRL pin can be used to override the internal 50mV
limit between the ISP, ISN pin to a lower set point for the
current control loop.
If the EN/UV pin is low, the LT8613 is shut down and
draws 1µA from the input. When the EN/UV pin is above
1V, the switching regulator will become active.
To optimize efficiency at light loads, the LT8613 operates
in Burst Mode operation in light load situations. Between
bursts, all circuitry associated with controlling the output
switch is shut down, reducing the input supply current to
1.7μA. In a typical application, 3μA will be consumed from
the input supply when regulating with no load. The SYNC
pin is tied low to use Burst Mode operation and can be
tied to a logic high to use pulse-skipping mode. If a clock
is applied to the SYNC pin the part will synchronize to an
external clock frequency and operate in pulse-skipping
mode. While in pulse-skipping mode the oscillator oper-
ates continuously and positive SW transitions are aligned
to the clock. During light loads, switch pulses are skipped
to regulate the output and the quiescent current will be
several hundred µA.
To improve efficiency across all loads, supply current to
internal circuitry can be sourced from the BIAS pin when
biased at 3.3V or above. Else, the internal circuitry will draw
current from VIN. The BIAS pin should be connected to
VOUT if the LT8613 output is programmed at 3.3V or above.
Comparators monitoring the FB pin voltage will pull the
PG pin low if the output voltage varies more than ±9%
(typical) from the set point, or if a fault condition is present.
The oscillator reduces the LT8613’s operating frequency
when the voltage at the FB pin is low. This frequency
foldback helps to control the inductor current when the
output voltage is lower than the programmed value which
occurs during start-up or overcurrent conditions. When
a clock is applied to the SYNC pin or the SYNC pin is
held DC high, the frequency foldback is disabled and the
switching frequency will slow down only during overcur-
rent conditions.
For more information www.linear.com/LT8613
8613f
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11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LT8613.PDF ] | |
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