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PDF LTM4618 Data sheet ( Hoja de datos )
| Número de pieza | LTM4618 | |
| Descripción | 6A DC/DC uModule Regulator | |
| Fabricantes | Linear | |
| Logotipo |  |
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LTM4618
6A DC/DC µModule
Regulator with Tracking and
Frequency Synchronization
FEATURES
DESCRIPTION
n Complete Standalone Power Supply
n Wide Input Voltage Range: 4.5V to 26.5V
n 6A DC Typical, 8A Peak Output Current
n 0.8V to 5V Output
n Output Voltage Tracking
n ±1.75% Maximum Total DC Error
n Current Mode Control/Fast Transient Response
n Phase-Lockable Fixed Frequency 250kHz to 780kHz
n On-Board Frequency Synchronization
n Selectable Burst Mode® Operation
n Power Good Voltage Indicator
n Output Overvoltage Protection
n Output Current Foldback Limiting
n 9mm × 15mm × 4.32mm LGA Package
APPLICATIONS
n Telecom and Networking Equipment
n Servers
n Storage Cards
n ATCA Cards
n Industrial Equipment
n Point of Load Regulation
n Medical Systems
The LTM®4618 is a complete 6A output switching mode
DC/DC power supply in a 9mm × 15mm × 4.32mm LGA
package. Included in the package are the switching con-
troller, power FETs, inductor and all support components.
Operating over an input voltage range of 4.5V to 26.5V,
the LTM4618 supports an output voltage range of 0.8V
to 5V set by a single external resistor. Its high efficiency
design delivers 6A continuous current (8A peak). Only a
few input and output capacitors are needed.
High switching frequency and a current mode architecture
enable a very fast transient response to line and load
changes without sacrificing stability. The device supports
frequency synchronization and output voltage tracking for
supply rail sequencing. Burst Mode operation or pulse-
skipping mode can be selected for light load operations.
Fault protection features include overvoltage protection,
overcurrent protection and foldback current limit for
short-circuit protection.
The LTM4618 is Pb-free and RoHS compliant.
L, LT, LTC, LTM, Linear Technology, the Linear logo, Burst Mode and μModule are registered
trademarks and LTpowerCAD is a trademark of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
TYPICAL APPLICATION
2.5V/6A DC/DC Power μModule® with 6V to 26.5V Input
VIN
6V to 26.5V
CIN
0.1μF
MODE/PLLIN INTVCC EXTVCC
VIN FREQ
COMP
TK/SS
LTM4618
VOUT
VFB
RUN
SGND
PGOOD
PGND
4618 TA01
28.7k
VOUT
2.5V/6A
COUT
Efficiency and Power Loss vs Load Current
95 3.0
EFFICIENCY
90
2.5
2.0
85
1.5
80
1.0
POWER LOSS
75 0.5
12VIN TO 2.5VOUT
24VIN TO 2.5VOUT
70 0
0123456
LOAD CURRENT (A)
4618 TA01b
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1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
LTM4618
Efficiency vs Load Current with
5VIN (CCM)
100
Efficiency vs Load Current with
12VIN (CCM)
100
Efficiency vs Load Current with
24VIN (CCM)
95
95 95 90
90
85
80 5V TO 0.8VOUT
5V TO 1.2VOUT
75 5V TO 1.5VOUT
5V TO 2.5VOUT
5V TO 3.3VOUT
70
0123456
LOAD CURRENT (A)
4618 G01
90
85
80 12V TO 1.2VOUT
12V TO 1.5VOUT
75 12V TO 2.5VOUT
12V TO 3.3VOUT
12V TO 5VOUT
70
0123456
LOAD CURRENT (A)
4618 G02
85
80
75 24V TO 2.5VOUT
24V TO 3.3VOUT
24V TO 5VOUT
70
0123456
LOAD CURRENT (A)
4618 G03
Efficiency vs Load Current with
Different Mode Settings
(12V to 3.3V)
100
VIN = 12V
90 VOUT = 3.3V
80
70
60
50
40
30
20
10
0
0.01
BURST
PULSE SKIP
CCM
0.1
LOAD CURRENT (A)
1
4618 G04
1.2V Transient Response
1.5V Transient Response
IOUT
1A/DIV
IOUT
1A/DIV
VOUT
50mV/DIV
VOUT
50mV/DIV
50μs/DIV
4618 G05
VIN = 12V AND VOUT = 1.2V AT 3A/μs LOAD STEP
COUT = 2= 22μF 6.3V CERAMIC CAPACITOR
1= 100μF 6.3V CERAMIC CAPACITOR
1= 220μF SANYO POSCAP
50μs/DIV
4618 G06
VIN = 12V AND VOUT = 1.5V AT 3A/μs LOAD STEP
COUT = 2= 22μF 6.3V CERAMIC CAPACITOR
1= 100μF 6.3V CERAMIC CAPACITOR
1= 220μF SANYO POSCAP
2.5V Transient Response
3.3V Transient Response
5V Transient Response
IOUT
1A/DIV
IOUT
1A/DIV
IOUT
1A/DIV
VOUT
50mV/DIV
VOUT
50mV/DIV
VOUT
100mV/DIV
50μs/DIV
4618 G07
VIN = 12V AND VOUT = 2.5V AT 3A/μs LOAD STEP
COUT = 2= 22μF 6.3V CERAMIC CAPACITOR
1= 100μF 6.3V CERAMIC CAPACITOR
1= 220μF SANYO POSCAP
50μs/DIV
4618 G08
VIN = 12V AND VOUT = 3.3V AT 3A/μs LOAD STEP
COUT = 2= 22μF 6.3V CERAMIC CAPACITOR
1= 100μF 6.3V CERAMIC CAPACITOR
1= 220μF SANYO POSCAP
50μs/DIV
4618 G09
VIN = 12V AND VOUT = 5V AT 3A/μs LOAD STEP
COUT = 2= 22μF 6.3V CERAMIC CAPACITOR
1= 100μF 6.3V CERAMIC CAPACITOR
1= 220μF SANYO POSCAP
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5 Page 
LTM4618
APPLICATIONS INFORMATION
Output Capacitors
The LTM4618 is designed for low output voltage ripple
noise. The bulk output capacitors defined as COUT are
chosen with low enough effective series resistance (ESR) to
meet the output voltage ripple and transient requirements.
COUT can be a low ESR tantalum capacitor, a low ESR
polymer capacitor or ceramic capacitor. The typical output
capacitance range is from 100μF to 300μF. Additional output
filtering may be required by the system designer if further
reduction of output ripple or dynamic transient spikes is
required. Table 4 shows a matrix of different output voltages
and output capacitors to minimize the voltage droop and
overshoot during a 3A/μs transient. The table optimizes the
total equivalent ESR and total bulk capacitance to optimize
the transient performance. Stability criteria are considered
in the Table 4 matrix, and the Linear Technology μModule
Power Design Tool is available for stability analysis. Mul-
tiphase operation will reduce effective output ripple as a
function of the number of phases. Application Note 77
discusses this noise reduction versus output ripple cur-
rent cancellation, but the output capacitance should be
considered carefully as a function of stability and transient
response. The Linear Technology μModule Power Design
Tool can calculate the output ripple reduction as the number
of implemented phases increases by N times.
Mode Selections and Phase-Locked Loop
The LTM4618 can be enabled to enter high efficiency
Burst Mode operation, constant-frequency, pulse-skipping
mode, or forced continuous conduction mode. To select
the forced continuous operation, tie the MODE/PLLIN pin
to ground. To select pulse-skipping mode of operation,
tie the MODE/PLLIN pin to INTVCC. To select Burst Mode
operation, float the pin.
A phase-locked loop (PLL) is available on the LTM4618
to synchronize the internal oscillator to an external clock
source that is connected to the MODE/PLLIN pin. The
incoming clock should be applied before the regulator’s
RUN pin is enabled.
Frequency Selection
The switching frequency of the LTM4618’s controller
can be selected using a DC voltage. If the MODE/PLLIN
pin is not being driven by an external clock source,
the FREQ pin can program the controller’s operating
frequency from 250kHz to 780kHz by connecting a re-
sistor divider as shown in Figure 21. When operating
below 400kHz, ensure the inductor ripple current is at
a reasonable level. The typical frequency is 750kHz.
But if the minimum on-time is reached, a lower frequency
needs to be set to increase the turn-on time. Otherwise, a
significant amount of cycle skipping can occur with cor-
respondingly larger ripple current and voltage ripple.
900
800
700
600
500
400
300
200
100
0
0
0.5 1 1.5
FREQ PIN VOLTAGE (V)
2 2.5
4618 F03
Figure 3. Relationship Between Switching
Frequency and Voltage at the FREQ Pin
Frequency Synchronization
The MODE/PLLIN pin allows the LTM4618 to be syn-
chronized to an external clock (between 250kHz to
780kHz) and the internal phase-locked loop allows the
LTM4618 to lock onto input clock phase as well. When
operating below 400kHz, ensure the inductor ripple cur-
rent is at a reasonable level. No more than 50% of the
load current is recommended. The FREQ pin has the
onboard loop filter for the PLL. The incoming clock must
be applied before the RUN pin is enabled. For applica-
tions powering the clock source from the LTM4618’s
INTVCC, the RUN pin has to be enabled in order to ac-
tivate INTVCC for the clock source. In this situation (see
Figure 22) the TK/SS pin can be used to soft-start the
regulator for 100ms using a ≈ 0.22μF capacitor. This will
allow the regulator to synchronize to the right frequency
before the regulator’s inductor ripple current peaks.
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11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LTM4618.PDF ] | |
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