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PDF LT8614 Data sheet ( Hoja de datos )
| Número de pieza | LT8614 | |
| Descripción | 4A Synchronous Step-Down Silent Switcher | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LT8614
42V, 4A Synchronous
Step-Down Silent Switcher
with 2.5µA Quiescent Current
Features
Description
n Silent Switcher™ Architecture:
Ultralow EMI/EMC Emissions
n High Efficiency at High Frequency
Up to 96% Efficiency at 1MHz
Up to 94% Efficiency at 2MHz
n Wide Input Voltage Range: 3.4V to 42V
n Ultralow Quiescent Current Burst Mode® Operation:
2.5μA IQ Regulating 12VIN to 3.3VOUT
Output Ripple < 10mVP-P
n Fast Minimum Switch-On Time: 30ns
n Low Dropout Under All Conditions: 200mV at 1A
n Safely Tolerates Inductor Saturation in Overload
n Adjustable and Synchronizable: 200kHz to 3MHz
n Peak Current Mode Operation
n Accurate 1V Enable Pin Threshold
n Internal Compensation
n Output Soft-Start and Tracking
n Small 18-Lead 3mm × 4mm QFN
Applications
n Automotive and Industrial Supplies
n General Purpose Step-Down
n GSM Power Supplies
The LT®8614 step-down regulator features Silent Switcher
architecture designed to minimize EMI/EMC emissions
while delivering high efficiency at frequencies up to 3MHz.
Assembled in a 3mm × 4mm QFN, the monolithic construc-
tion with integrated power switches and inclusion of all
necessary circuitry yields a solution with a minimal PCB
footprint. An ultralow 2.5µA quiescent current—with the
output in full regulation— enables applications requiring
highest efficiency at very small load currents. Transient
response remains excellent and output voltage ripple is
below 10mVP-P at any load, from zero to full current.
The LT8614 allows high VIN to low VOUT conversion at
high frequency with a fast minimum top switch on-time of
30ns. Operation is safe in overload even with a saturated
inductor.
Essential features are included and easy to use: An open-
drain PG pin signals when the output is in regulation. The
SYNC pin allows clock synchronization and choice of Burst
Mode operation or pulse-skipping mode. Soft-start and
tracking functionality is accessed via the TR/SS pin. An
accurate enable threshold can be set using the EN/UV pin
and a resistor at the RT pin programs switch frequency.
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
and Silent Switcher is a trademark of Linear Technology Corporation. All other trademarks are
the property of their respective owners.
Typical Application
VIN
5.8V TO 42V
5V 4A Step-Down Converter
4.7µF
1µF
10nF
1µF
41.2k
VIN1 EN/UV VIN2
GND1
GND2
PG LT8614 BST
SYNC/MODE SW
TR/SS
BIAS
INTVCC
RT
FB
GND
1µF
0.1µF 4.7µH
VOUT
5V
4A
4.7pF
1M
47µF
243k
fSW = 1MHz
8614 TA01a
12VIN to 5VOUT Efficiency
100
1MHz
95
2MHz
90
85
80
75
70
65
60
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
LOAD CURRENT (A)
8614 TA01b
For more information www.linear.com/LT8614
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1 page  
Typical Performance Characteristics
LT8614
Line Regulation
0.10
0.08
VOUT = 5V
ILOAD = 1A
0.06
0.04
0.02
0
–0.02
–0.04
–0.06
–0.08
–0.10
5
10 15 20 25 30 35
INPUT VOLTAGE (V)
40 45
8614 G10
No-Load Supply Current
5.0
4.5
VOUT = 3.3V
IN REGULATION
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0 5 10 15 20 25 30 35 40 45
INPUT VOLTAGE (V)
8614 G11
Top FET Current Limit vs Duty Cycle
9.0
8.5
8.0
7.5
7.0
6.5
6.0
0 0.2 0.4 0.6 0.8 1.0
DUTY CYCLE
8614 G13
Switch Drop
200
SWITCH CURRENT = 1A
175
150
125 TOP SWITCH
100
75
50
BOTTOM SWITCH
25
0
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
8614 G16
Top FET Current Limit
9.5
9.0
8.5
5% DC
8.0
7.5
7.0
6.5
6.0
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
8614 G14
Switch Drop
500
450
400
350
300
TOP SWITCH
250
200
150
100
50 BOTTOM SWITCH
0
01234
SWITCH CURRENT (A)
8614 G17
For more information www.linear.com/LT8614
No-Load Supply Current
25
VOUT = 3.3V
VIN = 12V
20 IN REGULATION
15
10
5
0
–55 –25
5 35 65 95
TEMPERATURE (°C)
125 155
8614 G12
Bottom FET Current Limit
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
8614 G15
Minimum On-Time
40
38
ILOAD = 1A, VSYNC = 0V
ILOAD = 1A, VSYNC = 3V
36
ILOAD = 2A
ILOAD = 4A
34
32
30
28
26
24
22
20
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
8614 G18
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5 Page 
LT8614
Operation
The LT8614 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 6.9A flowing through the
bottom switch, the next clock cycle will be delayed until
switch current returns to a safe level.
If the EN/UV pin is low, the LT8614 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 LT8614 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, 2.5μA 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 operates
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 LT8614 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 LT8614’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/LT8614
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11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LT8614.PDF ] | |
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