LINER LTM4605V High effi ciency buck-boost dc/dc î¼module Datasheet

LTM4605
High Efficiency
Buck-Boost DC/DC µModule
FEATURES
DESCRIPTION
n
The LTM®4605 is a high efficiency switching mode buckboost power supply. Included in the package are the
switching controller, power FETs, and support components.
Operating over an input voltage range of 4.5V to 20V, the
LTM4605 supports an output voltage range of 0.8V to
16V, set by a resistor. This high efficiency design delivers
up to 5A continuous current in boost mode (12A in buck
mode). Only the inductor, sense resistor, bulk input and
output capacitors are needed to finish the design.
n
n
n
n
n
n
n
n
n
n
n
Single Inductor Architecture Allows VIN Above,
Below or Equal to VOUT
Wide VIN Range: 4.5V to 20V
Wide VOUT Range: 0.8V to 16V
5A DC Typical (12A DC Typical at Buck Mode)
High Efficiency Up to 98%
Current Mode Control
Power Good Output Signal
Phase-Lockable Fixed Frequency: 200kHz to 400kHz
Ultra-Fast Transient Response
Current Foldback Protection
Output Overvoltage Protection
Small, Low Profile Surface Mount LGA Package
(15mm × 15mm × 2.8mm)
The low profile package enables utilization of unused space
on the bottom of PC boards for high density point of load
regulation. The high switching frequency and current
mode architecture enable a very fast transient response
to line and load changes. The LTM4605 can be frequency
synchronized with an external clock to reduce undesirable
frequency harmonics.
APPLICATIONS
n
n
n
Telecom, Servers and Networking Equipment
Industrial and Automotive Equipment
High Power Battery-Operated Devices
Fault protection features include overvoltage and foldback
current protection. The DC/DC μModule™ is offered in a
small and thermally enhanced 15mm × 15mm × 2.8mm LGA
package. The LTM4605 is Pb-free and RoHS compliant.
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. Burst Mode
is a registered trademark of Linear Technology Corporation. μModule is a trademark of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
Efficiency and Power Loss vs
Input Voltage
12V/5A Buck-Boost DC/DC μModule with 4.5V to 20V Input
99
CLOCK SYNC
10μF
35V
VIN
PLLIN V
OUT
RUN
LTM4605
4.7μH
SW1
SW2
RSENSE
SENSE+
0.1μF
6mΩ
SENSE–
SS
SGND
PGND
330μF
25V
VOUT
12V
5A
98
8
VOUT = 12V
ILOAD = 5A
f = 200kHz
7
97
6
96
5
95
4
94
3
93
2
92
1
91
VFB
POWER LOSS (W)
10μF
35V
FCB
ON/OFF
+
EFFICIENCY (%)
VIN
4.5V TO 20V
90
0
5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
VIN (V)
7.15k
4605 TA01
4605 TA01b
4605fa
1
LTM4605
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(See Table 6. Pin Assignment)
VIN ............................................................. –0.3V to 20V
VOUT ............................................................. 0.8V to 16V
INTVCC, EXTVCC, RUN, SS, PGOOD .............. –0.3V to 7V
SW1, SW2 .................................................... –5V to 20V
VFB, COMP ................................................ –0.3V to 2.4V
FCB, STBYMD ....................................... –0.3V to INTVCC
PLLIN ........................................................ –0.3V to 5.5V
PLLFLTR.................................................... –0.3V to 2.7V
Operating Temperature Range
(Note 2) ...............................................–40°C to 85°C
Junction Temperature ........................................... 125°C
Storage Temperature Range...................–55°C to 125°C
TOP VIEW
BANK 2
M
L
BANK 4
BANK 1
K
J
H
BANK 3
G
BANK 5
F
E
D
C
BANK 6
B
A
1
2
3
4
5
6
7
8
9
10
11
12
LGA PACKAGE
141-LEAD (15mm s 15mm s 2.8mm)
TJMAX = 125°C, θJP = 4°C/W
WEIGHT = 1.5g
ORDER INFORMATION
LEAD FREE FINISH
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTM4605EV#PBF
LTM4605V
141-Lead (15mm × 15mm × 2.8mm) LGA
–40°C to 85°C
LTM4605IV#PBF
LTM4605V
141-Lead (15mm × 15mm × 2.8mm) LGA
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
This product is only offered in trays. For more information go to: http://www.linear.com/packaging/
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the –40°C to 85°C
temperature range, otherwise specifications are at TA = 25°C, VIN = 12V. Per typical application (front page) configuration.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Input Specifications
Input DC Voltage
l
VIN(UVLO)
Undervoltage Lockout Threshold
VIN Falling
l
IQ(VIN)
Input Supply Bias Current
Normal
Standby
Shutdown Supply Current
VRUN = 0V, VSTBYMD > 2V
VRUN = 0V, VSTBYMD = Open
VIN(DC)
4.5
3.4
2.8
1.6
35
20
V
4
V
60
mA
mA
μA
4605fa
2
LTM4605
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the –40°C to 85°C
temperature range, otherwise specifications are at TA = 25°C, VIN = 12V. Per typical application (front page) configuration.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Output Specifications
IOUTDC
Output Continuous Current Range
VIN = 12V, VOUT = 5V
(See Output Current Derating Curves VIN = 6V, VOUT = 12V
for Different VIN, VOUT and TA)
ΔVFB/VFB(NOM)
Reference Voltage Line Regulation
Accuracy
VIN = 4.5V to 20V, VCOMP = 1.2V (Note 3)
ΔVFB/VFB(LOAD)
Load Regulation Accuracy
VCOMP = 1.2V to 0.7V
VCOMP = 1.2V to 1.8V (Note 3)
M1 tr
Turn-On Time (Note 4)
Drain to Source Voltage VDS = 12V, Bias
Current ISW = 10mA
50
ns
M1 tf
Turn-Off Time
Drain to Source Voltage VDS = 12V, Bias
Current ISW = 10mA
40
ns
M3 tr
Turn-On Time
Drain to Source Voltage VDS = 12V, Bias
Current ISW = 10mA
25
ns
M3 tf
Turn-Off Time
Drain to Source Voltage VDS = 12V, Bias
Current ISW = 10mA
20
ns
M2, M4 tr
Turn-On Time
Drain to Source Voltage VDS = 12V, Bias
Current ISW = 10mA
20
ns
M2, M4 tf
Turn-Off Time
Drain to Source Voltage VDS = 12V, Bias
Current ISW = 10mA
20
ns
t1d
M1 Off to M2 On Delay (Note 4)
Drain to Source Voltage VDS = 12V, Bias
Current ISW = 10mA
50
ns
t2d
M2 Off to M1 On Delay
Drain to Source Voltage VDS = 12V, Bias
Current ISW = 10mA
50
ns
t3d
M3 Off to M4 On Delay
Drain to Source Voltage VDS = 12V, Bias
Current ISW = 10mA
50
ns
t4d
M4 Off to M3 On Delay
Drain to Source Voltage VDS = 12V, Bias
Current ISW = 10mA
50
ns
Mode Transition 1
M2 Off to M4 On Delay
Drain to Source Voltage VDS = 12V, Bias
Current ISW = 10mA
220
ns
Mode Transition 2
M4 Off to M2 On Delay
Drain to Source Voltage VDS = 12V, Bias
Current ISW = 10mA
220
ns
M1 RDS(ON)
Static Drain-to-Source OnResistance
Bias Current ISW = 3A
6.5
mΩ
M2 RDS(ON)
Static Drain-to-Source OnResistance
Bias Current ISW = 3A
8
12
mΩ
M3 RDS(ON)
Static Drain-to-Source OnResistance
Bias Current ISW = 3A
8
12
mΩ
M4 RDS(ON)
Static Drain-to-Source OnResistance
Bias Current ISW = 3A
8
12
mΩ
12
5
l
l
A
A
0.002
0.02
%
0.15
–0.15
0.5
–0.5
%
%
Switch Section
Oscillator and Phase-Locked Loop
fNOM
Nominal Frequency
VPLLFLTR = 1.2V
260
300
330
kHz
fLOW
Lowest Frequency
VPLLFLTR = 0V
170
200
220
kHz
fHIGH
Highest Frequency
VPLLFLTR = 2.4V
340
400
440
kHz
RPLLIN
PLLIN Input Resistance
IPLLFLTR
Phase Detector Output Current
fPLLIN < fOSC
fPLLIN > fOSC
50
kΩ
–15
15
μA
μA
4605fa
3
LTM4605
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the –40°C to 85°C
temperature range, otherwise specifications are at TA = 25°C, VIN = 12V. Per typical application (front page) configuration.
SYMBOL
PARAMETER
CONDITIONS
VFB
Feedback Reference Voltage
VCOMP = 1.2V
VRUN
RUN Pin ON/OFF Threshold
ISS
Soft-Start Charging Current
VRUN = 2.2V
MIN
TYP
MAX
UNITS
0.792
0.8
0.808
V
1
1.6
2.2
V
1
1.7
Control Section
l
VSTBYMD(START)
Start-Up Threshold
VSTBYMD Rising
VSTBYMD(KA)
Keep-Active Power On Threshold
VSTBYMD Rising, VRUN = 0V
0.4
VFCB
Forced Continuous Threshold
IFCB
Forced Continuous Pin Current
VFCB = 0.85V
VBURST
Burst Inhibit (Constant Frequency)
Threshold
DF(BOOST, MAX)
μA
0.7
V
1.25
V
0.76
0.8
0.84
V
–0.3
–0.2
–0.1
μA
Measured at FCB Pin
5.3
5.5
V
Maximum Duty Factor
% Switch M4 On
99
DF(BUCK, MAX)
Maximum Duty Factor
% Switch M1 On
tON(MIN, BUCK)
Minimum On-Time for Synchronous Switch M1 (Note 5)
Switch in Buck Operation
RFBHI
Resistor Between VOUT and VFB pins
%
99
%
200
250
ns
99.5
100
100.5
kΩ
l
5.7
6
6.3
V
0.3
2
%
l
5.4
5.6
V
300
mV
Internal VCC Regulator
INTVCC
Internal VCC Voltage
VIN > 7V, VEXTVCC = 5V
ΔVLDO/VLDO
Internal VCC Load Regulation
ICC = 0mA to 20mA, VEXTVCC = 5V
VEXTVCC
EXTVCC Switchover Voltage
ICC = 20mA, VEXTVCC Rising
ΔVEXTVCC(HYS)
EXTVCC Switchover Hysteresis
ΔVEXTVCC
EXTVCC Switch Drop Voltage
ICC = 20mA, VEXTVCC = 6V
60
150
mV
160
–130
190
–150
mV
mV
Current Sensing Section
VSENSE(MAX)
Maximum Current Sense Threshold
l
l
Boost Mode
Buck Mode
–95
VSENSE(MIN, BUCK)
Minimum Current Sense Threshold
Discontinuous Mode
ISENSE
Sense Pins Total Source Current
VSENSE– = VSENSE+ = 0V
–6
mV
–380
μA
ΔVFBH
PGOOD Upper Threshold
VFB Rising
5.5
7.5
10
%
ΔVFBL
PGOOD Lower Threshold
VFB Falling
–5.5
–7.5
–10
%
ΔVFB(HYS)
PGOOD Hysteresis
VFB Returning
2.5
VPGL
PGOOD Low Voltage
IPGOOD = 2mA
0.2
IPGOOD
PGOOD Leakage Current
VPGOOD = 5V
PGOOD
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: The LTM4605E is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
%
0.3
V
1
μA
with statistical process controls. The LTM4605I is guaranteed over the
–40°C to 85°C temperature range.
Note 3: The LTM4605 is tested in a feedback loop that servos VCOMP to a
specified voltage and measures the resultant VFB.
Note 4: Turn-on and turn-off time are measured using 10% and 90%
levels. Transition delay time is measured using 50% levels.
Note 5: 100% tested at wafer level only.
4605fa
4
LTM4605
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Load Current
12VIN to 12VOUT
90
80
80
70
70
EFFICIENCY (%)
100
90
EFFICIENCY (%)
100
60
50
40
95
85
75
60
50
40
30
65
55
45
30
20
0
0.01
0.1
1
LOAD CURRENT (A)
35
20
CCM
DCM
BURST
10
CCM
DCM
BURST
10
0
0.01
10
0.1
1
LOAD CURRENT (A)
4605 G01
15
0.01
10
100
95
95
95
90
90
85
85
EFFICIENCY (%)
75
EFFICIENCY (%)
100
90
80
75
70
65
70
18VIN TO 5VOUT
12VIN TO 5VOUT
5VIN TO 5VOUT
65
60
0
3
6
9
LOAD CURRENT (A)
12
80
75
70
65
60
18VIN TO 3.3VOUT
12VIN TO 3.3VOUT
5VIN TO 3.3VOUT
55
50
0
3
6
9
LOAD CURRENT (A)
4605 G04
12
60
18VIN TO 2.5VOUT
12VIN TO 2.5VOUT
5VIN TO 2.5VOUT
55
50
0
IOUT
2A/DIV
IOUT
2A/DIV
VOUT
200mV/DIV
VOUT
200mV/DIV
VOUT
100mV/DIV
200μs/DIV
12
Transient Response from
18VIN to 12VOUT
IOUT
2A/DIV
LOAD STEP: 0A TO 3A AT CCM
OUTPUT CAPS: 4x 22μF CERAMIC CAPS AND
2x 180μF ELECTROLYTIC CAPS
2x 15mΩ SENSING RESISTORS
6
9
LOAD CURRENT (A)
4605 G06
Transient Response from
12VIN to 12VOUT
4605 G07
3
4605 G05
Transient Response from
6VIN to 12VOUT
200μs/DIV
100
Efficiency vs Load Current
1.5μH Inductor (CCM)
100
80
0.1
1
10
LOAD CURRENT (A)
4605 G03
Efficiency vs Load Current
1.5μH Inductor (CCM)
85
CCM
DCM
SKIP CYCLE
25
4605 G02
Efficiency vs Load Current
3.3μH Inductor (CCM)
EFFICIENCY (%)
Efficiency vs Load Current
18VIN to 12VOUT
EFFICIENCY (%)
Efficiency vs Load Current
6VIN to 12VOUT
(Refer to Figure 16)
4605 G08
LOAD STEP: 0A TO 3A AT CCM
OUTPUT CAPS: 4x 22μF CERAMIC CAPS AND
2x 180μF ELECTROLYTIC CAPS
2x 15mΩ SENSING RESISTORS
200μs/DIV
4605 G09
LOAD STEP: 0A TO 4A AT CCM
OUTPUT CAPS: 4x 22μF CERAMIC CAPS AND
2x 180μF ELECTROLYTIC CAPS
2x 15mΩ SENSING RESISTORS
4605fa
5
LTM4605
TYPICAL PERFORMANCE CHARACTERISTICS
Start-Up with 6VIN to 12VOUT at
IOUT = 5A
Start-Up with 18VIN to 12VOUT at
IOUT = 5A
VOUT
5V/DIV
VOUT
5V/DIV
IIN
5A/DIV
IIN
2A/DIV
IL
5A/DIV
IL
5A/DIV
50ms/DIV
4605 G10
50ms/DIV
4605 G11
0.22μF SOFT-START CAP
OUTPUT CAPS: 4x 22μF CERAMIC CAPS AND
2x 180μF ELECTROLYTIC CAPS
2x 15mΩ SENSING RESISTORS
0.22μF SOFT-START CAP
OUTPUT CAPS: 4x 22μF CERAMIC CAPS AND
2x 180μF ELECTROLYTIC CAPS
2x 15mΩ SENSING RESISTORS
Short Circuit with 6VIN to 12VOUT
at IOUT = 5A
Short Circuit with 18VIN to 12VOUT
at IOUT = 5A
VOUT
5V/DIV
VOUT
10V/DIV
IIN
5A/DIV
IIN
10A/DIV
20μs/DIV
4605 G12
OUTPUT CAPS: 4x 22μF CERAMIC CAPS AND
2x 180μF ELECTROLYTIC CAPS
2x 15mΩ SENSING RESISTORS
100μs/DIV
4605 G13
OUTPUT CAPS: 4x 22μF CERAMIC CAPS AND
2x 180μF ELECTROLYTIC CAPS
2x 15mΩ SENSING RESISTORS
4605fa
6
LTM4605
PIN FUNCTIONS
VIN (Bank 1): Power Input Pins. Apply input voltage between these pins and PGND pins. Recommend placing
input decoupling capacitance directly between VIN pins
and PGND pins.
VOUT (Bank 5): Power Output Pins. Apply output load
between these pins and PGND pins. Recommend placing
output decoupling capacitance directly between these pins
and PGND pins.
PGND (Bank 6): Power Ground Pins for Both Input and
Output Returns.
SW1, SW2 (Bank 4, Bank 2): Switch Nodes. The power
inductor is connected between SW1 and SW2.
RSENSE (Bank 3): Sensing Resistor Pin. The sensing resistor is connected from this pin to PGND.
SENSE+ (Pin A4): Positive Input to the Current Sense and
Reverse Current Detect Comparators.
SENSE– (Pin A5): Negative Input to the Current Sense and
Reverse Current Detect Comparators.
EXTVCC (Pin F6): External VCC Input. When EXTVCC exceeds
5.7V, an internal switch connects this pin to INTVCC and
shuts down the internal regulator so that the controller and
gate drive power is drawn from EXTVCC. Do not exceed
7V at this pin and ensure that EXTVCC < VIN.
INTVCC (Pin F5): Internal 6V Regulator Output. This pin is
for additional decoupling of the 6V internal regulator.
PLLIN (Pin B9): External Clock Synchronization Input
to the Phase Detector. This pin is internally terminated
to SGND with a 50k resistor. The phase-locked loop will
force the rising bottom gate signal of the controller to be
synchronized with the rising edge of PLLIN signal.
PLLFLTR (Pin B8): The lowpass filter of the phase-locked
loop is tied to this pin. This pin can also be used to set the
frequency of the internal oscillator with an AC or DC voltage.
See the Applications Information section for details.
STBYMD (Pin A10): LDO Control Pin. Determine whether
the internal LDO remains active when the controller is shut
down. See Operations section for details. If the STBYMD
pin is pulled to ground, the SS pin is internally pulled to
ground to disable start-up and thereby providing a single
control pin for turning off the controller. An internal decoupling capacitor is tied to this pin.
VFB (Pin B6): The Negative Input of the Error Amplifier.
Internally, this pin is connected to VOUT with a 100k precision resistor. Different output voltages can be programmed
with an additional resistor between VFB and SGND pins.
See the Applications Information section.
FCB (Pin A9): Forced Continuous Control Input. The voltage
applied to this pin sets the operating mode of the module.
When the applied voltage is less than 0.8V, the forced
continuous current mode is active in boost operation and
the skip cycle mode is active in buck operation. When the
pin is tied to INTVCC, the constant frequency discontinuous
current mode is active in buck or boost operation. See the
Applications Information section.
SGND (Pin A7): Signal Ground Pin. This pin connects to
PGND at output capacitor point.
COMP (Pin B7): Current Control Threshold and Error
Amplifier Compensation Point. The current comparator
threshold increases with this control voltage. The voltage
ranges from 0V to 2.4V.
PGOOD (Pin B5): Output Voltage Power Good Indicator.
Open drain logic output that is pulled to ground when the
output voltage is not within ±10% of the regulation point,
after a 25μs power bad mask timer expires.
RUN (Pin A8): Run Control Pin. A voltage below 1.6V will
turn off the module. There is a 100k resistor between the
RUN pin and SGND in the module. Do not apply more than
6V to this pin. See Applications Information section.
SS (Pin A6): Soft-Start Pin. Soft-start reduces the input
power sources’ surge currents by gradually increasing the
controller’s current limit.
4605fa
7
LTM4605
SIMPLIFIED BLOCK DIAGRAM
VIN
4.5V TO 20V
EXTVCC
C1
CIN
M1
SW2
INTVCC
M2
PGOOD
L
SW1
RUN
ON/OFF
VOUT
100k
12V
5A
STBYMD
CO1
M3
COUT
0.1μF
100k
COMP
VFB
M4
INT
COMP
CONTROLLER
RFB
7.15k
RSENSE
SENSE+
SS
SS
0.1μF
PLLIN
INT
FILTER
RSENSE
SENSE–
PLLFLTR
PGND
INT
FILTER
FCB
SGND
1000pF
TO PGND PLANE AS
SHOWN IN FIGURE 13
4605 BD
Figure 1. Simplified LTM4605 Block Diagram
DECOUPLING REQUIREMENTS TA = 25°C. Use Figure 1 configuration.
SYMBOL
PARAMETER
CONDITIONS
CIN
External Input Capacitor Requirement
(VIN = 4.5V to 20V, VOUT = 12V)
IOUT = 5A
MIN
10
COUT
External Output Capacitor Requirement
(VIN = 4.5V to 20V, VOUT = 12V)
IOUT = 5A
200
TYP
MAX
UNITS
μF
300
μF
4605fa
8
LTM4605
OPERATION
Power Module Description
The LTM4605 is a non-isolated buck-boost DC/DC power
supply. It can deliver a wide range output voltage from
0.8V to 16V over a wide input range from 4.5V to 20V,
by only adding the sensing resistor, inductor and some
external input and output capacitors. It provides precisely
regulated output voltage programmable via one external
resistor. The typical application schematic is shown in
Figure 16.
The LTM4605 has an integrated current mode buck-boost
control, ultralow RDS(ON) FETs with fast switching speed
and integrated Schottky diodes. With current mode control
and internal feedback loop compensation, the LTM4605
module has sufficient stability margins and good transient
performance under a wide range of operating conditions
and with a wide range of output capacitors. The frequency
of LTM4605 can be operated from 200kHz to 400kHz by
setting the voltage on the PLLFLTR pin. Alternatively, its
frequency can be synchronized by the input clock signal
from the PLLIN pin. The typical switching frequency is
400kHz.
The Burst Mode and skip-cycle mode operations can
be enabled at light loads in the LTM4605 to improve its
efficiency, while the forced continuous mode and discontinuous mode operations are used for constant frequency
applications. Foldback current limiting is activated in an
overcurrent condition as VFB drops. Internal overvoltage
and undervoltage comparators pull the open-drain PGOOD
output low if the output feedback voltage exits the ±10%
window around the regulation point. Pulling the RUN pin
below 1.6V forces the controller into its shutdown state.
If an external bias supply is applied on the EXTVCC pin, then
an efficiency improvement will occur due to the reduced
power loss in the internal linear regulator. This is especially
true at the higher input voltage range.
APPLICATIONS INFORMATION
The typical LTM4605 application circuit is shown in
Figure 16. External component selection is primarily
determined by the maximum load current and output
voltage. Refer to Table 3 for specific external capacitor
requirements for a particular application.
Table 1. RFB Resistor (0.5%) vs Various Output Voltages
VOUT
0.8V
1.5V
2.5V
3.3V
5V
6V
RFB
Open
115k
47.5k
32.4k
19k
15.4k
VOUT
8V
9V
10V
12V
15V
16V
RFB
11k
9.76k
8.66k
7.15k
5.62k
5.23k
Output Voltage Programming
The PWM controller has an internal 0.8V±1% reference
voltage. As shown in the Block Diagram, a 100k, 0.5%
internal feedback resistor connects VOUT and VFB pins
together. Adding a resistor RFB from the VFB pin to the
SGND pin programs the output voltage:
VOUT = 0.8 V •
100k + RFB
RFB
Operation Frequency Selection
The LTM4605 uses current mode control architecture at
constant switching frequency, which is determined by the
internal oscillator’s capacitor. This internal capacitor is
charged by a fixed current plus an additional current that
is proportional to the voltage applied to the PLLFLTR pin.
4605fa
9
LTM4605
APPLICATIONS INFORMATION
The PLLFLTR pin can be grounded to lower the frequency
to 200kHz or tied to 2.4V to yield approximately 400kHz.
When PLLIN is left open, the PLLFLTR pin goes low, forcing the oscillator to its minimum frequency.
A graph for the voltage applied to the PLLFLTR pin vs
frequency is given in Figure 2. As the operating frequency
increases, the gate charge losses will be higher, thus the
efficiency is low. The maximum switching frequency is
approximately 400kHz.
450
OPERATING FREQUENCY (kHz)
400
350
300
250
200
150
100
50
0
0
1.0
1.5
2.0
0.5
PLLFLTR PIN VOLTAGE (V)
2.5
4605 F02
Figure 2. Frequency vs PLLFLTR Pin Voltage
FREQUENCY SYNCHRONIZATION
The LTM4605 can also be synchronized to an external
source via the PLLIN pin instead of adjusting the voltage on
the PLLFLTR pin directly. The power module has a phaselocked loop comprised of an internal voltage controlled
oscillator and a phase detector. This allows turning on the
internal top MOSFET for locking to the rising edge of the
external clock. A pulse detection circuit is used to detect
a clock on the PLLIN pin to turn on the phase lock loop.
The input pulse width of the clock has to be at least 400ns,
and 2V in amplitude. The synchronized frequency ranges
from 200kHz to 400kHz, corresponding to a DC voltage
input from 0V to 2.4V at PLLFLTR. During the start up of
the regulator, the phase-lock loop function is disabled.
Low Current Operation
To improve the efficiency at low current operation, LTM4605
provides three modes for both buck and boost operations
by accepting a logic input on the FCB pin. Table 2 shows
the different operation modes.
Table 2. Different Operating Modes
FCB PIN
BUCK
BOOST
0V to 0.75V
Force Continuous Mode
Force Continuous Mode
0.85V to 5V
Skip-Cycle Mode
Burst Mode Operation
>5.3V
DCM with Constant Freq
DCM with Constant Freq
When the FCB pin voltage is lower than 0.8V, the controller
behaves as a continuous, PWM current mode synchronous
switching regulator. When the FCB pin voltage is below
VINTVCC – 1V, but greater than 0.8V, the controller enters
Burst Mode operation in boost operation or enters skipcycle mode in buck operation. During boost operation,
Burst Mode operation is activated if the load current is
lower than the preset minimum output current level. The
MOSFETs will turn on for several cycles, followed by a
variable “sleep” interval depending upon the load current.
During buck operation, skip-cycle mode sets a minimum
positive inductor current level. In this mode, some cycles
will be skipped when the output load current drops below
1% of the maximum designed load in order to maintain
the output voltage.
When the FCB pin is tied to the INTVCC pin, the controller
enters constant frequency discontinuous current mode
(DCM). For boost operation, if the output voltage is high
enough, the controller can enter the continuous current
buck mode for one cycle to discharge inductor current.
In the following cycle, the controller will resume DCM
boost operation. For buck operation, constant frequency
discontinuous current mode is turned on if the preset
minimum negative inductor current level is reached. At
very light loads, this constant frequency operation is not as
efficient as Burst Mode operation or skip-cycle, but does
provide low noise, constant frequency operation.
Input Capacitors
In boost mode, since the input current is continuous, only
minimum input capacitors are required. However, the input
current is discontinuous in buck mode, so the selection
of input capacitor CIN is driven by the need of filtering the
input square wave current.
4605fa
10
LTM4605
APPLICATIONS INFORMATION
For a buck converter, the switching duty-cycle can be
estimated as:
D=
VOUT
VIN
Without considering the inductor current ripple, the RMS
current of the input capacitor can be estimated as:
ICIN(RMS) =
IOUT(MAX )
η
• D • (1− D)
In the above equation, η is the estimated efficiency of the
power module. CIN can be a switcher-rated electrolytic
aluminum capacitor, OS-CON capacitor or high volume
ceramic capacitors. Note the capacitor ripple current ratings are often based on temperature and hours of life. This
makes it advisable to properly derate the input capacitor,
or choose a capacitor rated at a higher temperature than
required. Always contact the capacitor manufacturer for
derating requirements.
Output Capacitors
Inductor Selection
The inductor is chiefly decided by the required ripple current and the operating frequency. The inductor current
ripple ΔIL is typically set to 20% to 40% of the maximum
inductor current. In the inductor design, the worst cases
in continuous mode are considered as follows:
LBOOST ≥
In boost mode, the discontinuous current shifts from the
input to the output, so the output capacitor COUT must be
capable of reducing the output voltage ripple.
For boost and buck modes, the steady ripple due to charging and discharging the bulk capacitance is given by:
VRIPPLE,BOOST =
VRIPPLE,BUCK =
The LTM4605 is designed for low output voltage ripple.
The bulk output capacitors defined as COUT are chosen
with low enough ESR to meet the output voltage ripple
and transient requirements. COUT can be a low ESR tantalum capacitor, a low ESR polymer capacitor or a ceramic
capacitor. Multiple capacitors can be placed in parallel to
meet the ESR and RMS current handling requirements. The
typical capacitance is 300μF. Additional output filtering may
be required by the system designer, if further reduction of
output ripple or dynamic transient spike is required. Table
3 shows a matrix of different output voltages and output
capacitors to minimize the voltage droop and overshoot
at a current transient.
(
IOUT(MAX ) • VOUT − VIN(MIN)
)
COUT • VOUT • f
(
VOUT • VIN(MAX ) − VOUT
)
8 • L • COUT • VIN(MAX ) • f 2
The steady ripple due to the voltage drop across the ESR
(effective series resistance) is given by:
VESR,BUCK = ΔIL(MAX ) • ESR
VESR,BOOST = IL(MAX ) • ESR
LBUCK ≥
(
VIN • VOUT(MAX ) − VIN
)
VOUT(MAX ) • f • IOUT(M
MAX ) • Ripple%
(
VOUT • VIN(MAX ) − VOUT
)
VIN(MAX ) • f • IOUT(MAX ) • Ripple%
where:
f is operating frequency, Hz
Ripple% is allowable inductor current ripple, %
VOUT(MAX) is maximum output voltage, V
VIN(MAX) is maximum input voltage, V
VOUT is output voltage, V
IOUT(MAX) is maximum output load current, A
The inductor should have low DC resistance to reduce the
I2R losses, and must be able to handle the peak inductor
current without saturation. To minimize radiated noise,
use a toroid, pot core or shielded bobbin inductor. Please
refer to Table 3 for the recommended inductors for different cases.
4605fa
11
LTM4605
APPLICATIONS INFORMATION
RSENSE Selection and Maximum Output Current
RSENSE is chosen based on the required inductor current.
Since the maximum inductor valley current at buck mode
is much lower than the inductor peak current at boost
mode, different sensing resistors are suggested to use
in buck and boost modes.
The current comparator threshold sets the peak of the
inductor current in boost mode and the maximum inductor
valley current in buck mode. In boost mode, the allowed
maximum average load current is:
⎛ 160mV ΔIL ⎞ VIN
IOUT(MAX,BOOST) = ⎜
−
•
2 ⎟⎠ VOUT
⎝ RSENSE
where ΔIL is peak-to-peak inductor ripple current.
In buck mode, the allowed maximum average load current is:
IOUT(MAX,BUCK ) =
130mV ΔIL
+
RSENSE
2
The maximum current sensing RSENSE value for the boost
mode is:
the internal reference and the output voltage. The total
soft-start time can be calculated as:
t SOFTSTART =
2.4V • CSS
1.7µA
When the RUN pin falls below 1.6V, then soft-start pin is
reset to allow for proper soft-start control when the regulator is enabled again. Current foldback and force continuous
mode are disabled during the soft-start process. The softstart function can also be used to control the output ramp
up time, so that another regulator can be easily tracked.
Do not apply more than 6V to the SS pin.
Run Enable
The RUN pin is used to enable the power module. The pin
can be driven with a logic input, and not exceed 6V.
The RUN pin can also be used as an undervoltage lockout
(UVLO) function by connecting a resistor from the input
supply to the RUN pin. The equation:
V _ UVLO =
R + 100k
• 1.6 V
100k
RSENSE(MAX,BOOST) =
Power Good
2 • 160mV • VIN
2 • IOUT(MAX,BOOST) • VOUT + ΔIL • VIN
The PGOOD pin is an open drain pin that can be used to
monitor valid output voltage regulation. This pin monitors
a ±7.5% window around the regulation point, and tracks
with margining.
The maximum current sensing RSENSE value for the buck
mode is:
RSENSE(MAX,BUCK ) =
2 • 130mV
2 • IOUT(MAX,BUCK ) – ΔIL
A 20% to 30% margin on the calculated sensing resistor is
usually recommended. Please refer to Table 3 for the recommended sensing resistors for different applications.
Soft-Start
The SS pin provides a means to soft-start the regulator.
A capacitor on this pin will program the ramp rate of the
output voltage. A 1.7μA current source will charge up the
external soft-start capacitor. This will control the ramp of
COMP Pin
This pin is the external compensation pin. The module
has already been internally compensated for most output
voltages. A spice model will be provided for other control
loop optimization.
Fault Conditions: Current Limit and Overcurrent
Foldback
LTM4605 has a current mode controller, which inherently
limits the cycle-by-cycle inductor current not only in steady
state operation, but also in transient. Refer to Table 3.
To further limit current in the event of an overload condition, the LTM4605 provides foldback current limiting. If the
4605fa
12
LTM4605
APPLICATIONS INFORMATION
output voltage falls by more than 70%, then the maximum
output current is progressively lowered to about 30% of
its full current limit value for boost mode and about 40%
for buck mode.
Standby Mode (STBYMD)
The standby mode (STBYMD) pin provides several choices
for start-up and standby operational modes. If the pin is
pulled to ground, the SS pin is internally pulled to ground,
preventing start-up and thereby providing a single control
pin for turning off the controller. If the pin is left open or
decoupled with a capacitor to ground, the SS pin is internally
provided with a starting current, permitting external control
for turning on the controller. If the pin is connected to a
voltage greater than 1.25V, the internal regulator (INTVCC)
will be on even when the controller is shut down (RUN
pin voltage <1.6V). In this mode, the onboard 6V linear
regulator can provide power to keep-alive functions such
as a keyboard controller.
INTVCC and EXTVCC
An internal P-channel low dropout regulator produces 6V
at the INTVCC pin from the VIN supply pin. INTVCC powers
the control chip and internal circuitry within the module.
The LTM4605 also provides the external supply voltage pin
EXTVCC. When the voltage applied to EXTVCC rises above
5.7V, the internal regulator is turned off and an internal
switch connects the EXTVCC pin to the INTVCC pin thereby
supplying internal power. The switch remains close as long
as the voltage applied to EXTVCC remains above 5.5V. This
allows the MOSFET driver and control power to be derived
from the output when (5.7V < VOUT < 7V) and from the
internal regulator when the output is out of regulation (startup, short-circuit). If more current is required through the
EXTVCC switch than is specified, an external Schottky diode
can be interposed between the EXTVCC and INTVCC pins.
Ensure that EXTVCC ≤ VIN.
The following list summarizes the three possible connections for EXTVCC:
1. EXTVCC left open (or grounded). This will cause INTVCC
to be powered from the internal 6V regulator at the cost
of a small efficiency penalty.
2. EXTVCC connected directly to VOUT (5.7V < VOUT <
7V). This is the normal connection for a 6V regulator and
provides the highest efficiency.
3. EXTVCC connected to an external supply. If an external
supply is available in the 5.5V to 7V range, it may be
used to power EXTVCC provided it is compatible with the
MOSFET gate drive requirements.
Thermal Considerations and Output Current Derating
In different applications, the LTM4605 operates in a variety
of thermal environments. The maximum output current is
limited by the environmental thermal condition. Sufficient
cooling should be provided to ensure reliable operation.
When the cooling is limited, proper output current de-rating is
necessary, considering ambient temperature, airflow, input/
output condition, and the need for increased reliability.
The power loss curves in Figures 5 and 6 can be used
in coordination with the load current derating curves in
Figures 7 to 12 for calculating an approximate θJA for
the module. Column designation delineates between no
heatsink, and a BGA heatsink. Each of the load current
derating curves will lower the maximum load current as
a function of the increased ambient temperature to keep
the maximum junction temperature of the power module
at 115°C maximum. This will allow a safe margin to work
at the maximum operating temperature below 125°C.
Each of the derating curves and the power loss curve that
corresponds to the correct output voltage can be used to
solve for the approximate θJA of the condition. A complete
explanation of the thermal characteristics is provided in
the thermal application note for the LTM4605.
DESIGN EXAMPLES
Buck Mode Operation
As a design example, use input voltage VIN = 12V to 20V,
VOUT = 12V and f = 400kHz.
Set the PLLFLTR pin at 2.4V or more for 400kHz frequency
and connect FCB to ground for continuous current mode
operation. If a divider is used to set the frequency as shown
in Figure 14, the bottom resistor R3 is recommended not
to exceed 1k.
4605fa
13
LTM4605
APPLICATIONS INFORMATION
To set the output voltage at 12V, the resistor RFB from VFB
pin to ground should be chosen as:
RFB =
0.8 V • 100k
≈ 7.15k
VOUT − 0.8 V
To choose a proper inductor, we need to know the current
ripples at different input voltages. The inductor should
be chosen by considering the worst case in the practical
operating region. If the maximum output power P is 150W
at buck mode, we can get the current ripple ratio of the
current ripple ΔIL to the maximum inductor current IL as
follows:
ΔIL ( VIN – VOUT ) • VOUT 2
=
IL
VIN • L • f • P
For the input capacitor, use a low ESR sized capacitor to
handle the maximum RMS current. Input capacitors are
required to be placed adjacent to the module. In Figure 14,
the 10μF ceramic input capacitors are selected for their
ability to handle the large RMS current into the converter.
The 100μF bulk capacitor is only needed if the input source
impedance is compromised by long inductive leads or
traces.
For the output capacitor, the output voltage ripple and
transient requirements require low ESR capacitors. If
assuming that the ESR dominates the output ripple, the
output ripple is as follows:
ΔVOUT(P-P) = ESR • ΔIL
Figure 3 shows the current ripple ratio at different input
voltages based on the inductor values: 1.5μH, 2.5μH,
3.3μH and 4.7μH. If we need 30% ripple current ratio at
all inputs, the 3.3μH inductor can be selected.
CURRENT RIPPLE RATIO
Consider the safety margin about 30%, we can choose
the sensing resistor as 8mΩ.
If a total low ESR of about 5mΩ is chosen for output capacitors, the maximum output ripple of 17.5mV occurs at
the input voltage of 20V with the current ripple at 3.5A.
0.8
Boost Mode Operation
0.6
For boost mode operation, use input voltage VIN = 5V to
12V, VOUT = 12V and f = 400kHz.
1.5μH
Set the PLLFLTR pin and RFB as in buck mode.
0.4
2.5μH
3.3μH
0.2
4.7μH
0
12
16
18
14
INPUT VOLTAGE VIN (V)
20
4605 F03
Figure 3. Current Ripple Ratio at Different Inputs for Buck Mode
At buck mode, sensing resistor selection is based on
the maximum output current and the allowed maximum
sensing threshold 130mV.
RSENSE =
If the maximum output power P is 60W at boost mode
and the module efficiency η is about 95%, we can get
the current ripple ratio of the current ripple ΔIL to the
maximum inductor current IL as follows:
ΔIL ( VOUT − VIN ) • VIN2 η
=
IL
VOUT • L • f • P
Figure 4. shows the current ripple ratio at different input
voltages based on the inductor values: 1.5μH, 2.5μH,
3.3μH and 4.7μH. If we need 30% ripple current ratio at
all inputs, the 3.3μH inductor can be selected.
2 • 130mV
2 • (P / VOUT ) − ΔIL
4605fa
14
LTM4605
APPLICATIONS INFORMATION
output ripple is as follows:
0.6
ΔVOUT(P-P) = ESR • IL(MAX )
CURRENT RIPPLE RATIO
1.5μH
0.4
If a total low ESR about 5mΩ is chosen for output capacitors, the maximum output ripple of 70mV occurs at the input
voltage of 5V with the peak inductor current at 14A.
2.5μH
3.3μH
0.2
4.7μH
Wide Input Mode Operation
0
5
6
8
9
10
7
INPUT VOLTAGE VIN (V)
11
12
4605 F04
Figure 4. Current Ripple Ratio at Different Inputs for Boost Mode
At boost mode, sensing resistor selection is based on
the maximum input current and the allowed maximum
sensing threshold 160mV.
RSENSE =
2 • 160mV
P
2•
+ ΔIL
η • VIN(MIN)
Consider the safety margin about 30%, we can choose
the sensing resistor as 7mΩ.
If a wide input range is required from 5V to 20V, the module
will work in different operation modes. If input voltage
VIN = 5V to 20V, VOUT = 12V and f = 400kHz, the design
needs to consider the worst case in buck or boost mode
design. Therefore, the maximum output power is limited
to 60W. The sensing resistor is chosen at 7mΩ, the input
capacitor is the same as the buck mode design and the
output capacitor uses the boost mode design. Since the
maximum output ripple normally occurs at boost mode
in the wide input mode design, more inductor ripple current, up to 150% of the inductor current, is allowed at
buck mode to meet the ripple design requirement. Thus,
a 3.3μH inductor is chosen at the wide input mode. The
maximum output ripple voltage is still 70mV if the total
ESR is about 5mΩ.
For the input capacitor, only minimum capacitors are
needed to handle the maximum RMS current, since it
is a continuous input current at boost mode. A 100μF
capacitor is only needed if the input source impedance is
compromised by long inductive leads or traces.
Additionally, the current limit may become very high when
the module runs at buck mode due to the low sensing
resistor used in the wide input mode operation.
Since the output capacitors at boost mode need to filter
the square wave current, more capacitors are expected
to achieve the same output ripples as the buck mode. If
assuming that the ESR dominates the output ripple, the
The LTM4605 modules do not provide isolation from VIN to
VOUT. There is no internal fuse. If required, a slow blow fuse
with a rating twice the maximum input current needs to be
provided to protect each unit from catastrophic failure.
Safety Considerations
4605fa
15
LTM4605
APPLICATIONS INFORMATION
Table 3. Typical Components (f = 400kHz)
COUT1 VENDORS
PART NUMBER
COUT2 VENDORS
PART NUMBER
TDK
C4532X7R1E226M (22μF, 25V)
Sanyo
16SVP180MX (180μF, 16V)
INDUCTOR VENDORS
PART NUMBER
RSENSE VENDORS
PART NUMBER
Toko
FDA1254
Vishay
Power Metal Strip Resistors WSL1206-18
Sumida
CDEP134, CDEP145
Panasonic
Thick Film Chip Resistors ERJ12
VIN
(V)
VOUT
(V)
RSENSE
(0.5W RATING)
Inductor
(μH)
CIN
(CERAMIC)
CIN
(BULK)
COUT1
(CERAMIC)
COUT2
(BULK)
IOUT(MAX)*
(A)
5
2.5
2x 16mΩ 0.5W
1
3x 10μF 25V
150μF 35V
2x 22μF 25V
1x 180μF 16V
12
12
2.5
2x 18mΩ 0.5W
1.5
2x 10μF 25V
150μF 35V
2x 22μF 25V
1x 180μF 16V
12
5
3.3
2x 18mΩ 0.5W
1
3x 10μF 25V
150μF 35V
2x 22μF 25V
1x 180μF 16V
12
12
3.3
2x 18mΩ 0.5W
1.5
2x 10μF 25V
150μF 35V
2x 22μF 25V
1x 180μF 16V
12
12
5
2x 18mΩ 0.5W
2.2
3x 10μF 25V
150μF 35V
2x 22μF 25V
1x 180μF 16V
12
20
5
2x 18mΩ 0.5W
2.5
2x 10μF 25V
150μF 35V
2x 22μF 25V
1x 180μF 16V
12
5
8
2x 14mΩ 0.5W
1.5
None
150μF 35V
4x 22μF 25V
2x 180μF 16V
8
12
8
2x 18mΩ 0.5W
2.2
3x 10μF 25V
150μF 35V
2x 22μF 25V
2x 180μF 16V
12
20
8
2x 18mΩ 0.5W
3.3
3x 10μF 25V
150μF 35V
2x 22μF 25V
2x 180μF 16V
12
5
10
2x 16mΩ 0.5W
2.2
None
150μF 35V
4x 22μF 25V
2x 180μF 16V
6
15
10
2x 18mΩ 0.5W
2.2
3x 10μF 25V
150μF 35V
2x 22μF 25V
2x 180μF 16V
12
20
10
2x 18mΩ 0.5W
3.3
3x 10μF 25V
150μF 35V
2x 22μF 25V
2x 180μF 16V
12
6
12
2x 14mΩ 0.5W
2.2
None
150μF 35V
4x 22μF 25V
2x 180μF 16V
6
16
12
2x 16mΩ 0.5W
2.2
2x 10μF 25V
150μF 35V
2x 22μF 25V
2x 180μF 16V
12
20
12
2x 18mΩ 0.5W
3.3
3x 10μF 25V
150μF 35V
2x 22μF 25V
2x 180μF 16V
12
5
16
2x 15mΩ 0.5W
3.3
None
150μF 35V
4x 22μF 25V
2x 150μF 20V
3.5
8
16
2x 14mΩ 0.5W
3.3
None
150μF 35V
4x 22μF 25V
2x 150μF 20V
6
12
16
2x 12mΩ 0.5W
2.2
None
150μF 35V
4x 22μF 25V
2x 150μF 20V
10
20
16
2x 18mΩ 0.5W
2.2
2x 10μF 25V
150μF 35V
2x 22μF 25V
2x 150μF 20V
12
INDUCTOR MANUFACTURER
WEBSITE
PHONE NUMBER
Sumida
www.sumida.com
408-321-9660
Toko
www.toko.com
847-297-0070
SENSING RESISTOR MANUFACTURER
WEBSITE
PHONE NUMBER
Panasonic
www.panasonic.com/industrial/components
949-462-1816
KOA
www.koaspeer.com
814-362-5536
Vishay
www.vishay.com
800-433-5700
*Maximum load current is based on the Linear Technology Demo board DC1198A at room temperture with natural convection. Poor board layout design
may decrease the maximum load current.
4605fa
16
LTM4605
TYPICAL APPLICATIONS
9
8
8
7
7
20VIN TO 12VOUT
6
5VIN TO 16VOUT
POWER LOSS (W)
POWER LOSS (W)
Power loss includes all external components
6
5
4
3
5
4
3
2
2
5VIN TO 12VOUT
1
1
0
0
0
1
2
3
4
OUTPUT CURRENT (A)
0
5
2
4
6
8
OUTPUT CURRENT (A)
10
4605 F05
4605 F06
Figure 5. 5VIN Power Loss
Figure 6. 20VIN Power Loss
5
MAXIMUM LOAD CURRENT (A)
MAXIMUM LOAD CURRENT (A)
5
4
3
2
1
5VIN TO 12VOUT WITH 0LFM
5VIN TO 12VOUT WITH 200LFM
5VIN TO 12VOUT WITH 400LFM
0
25
35
4
3
2
1
5VIN TO 12VOUT WITH 0LFM
5VIN TO 12VOUT WITH 200LFM
5VIN TO 12VOUT WITH 400LFM
0
45 55 65 75 85 95 105 115
AMBIENT TEMPERATURE (°C)
25
45
65
85
105
AMBIENT TEMPERATURE (°C)
4605 F07
Figure 8. 5VIN to 12VOUT with Heatsink
4.0
3.5
3.5
MAXIMUM LOAD CURRENT (A)
4.0
3.0
2.5
2.0
1.5
1.0
5VIN TO 16VOUT WITH 0LFM
5VIN TO 16VOUT WITH 200LFM
5VIN TO 16VOUT WITH 400LFM
0.5
0
25
35
3.0
2.5
2.0
1.5
1.0
5VIN TO 16VOUT WITH 0LFM
5VIN TO 16VOUT WITH 200LFM
5VIN TO 16VOUT WITH 400LFM
0.5
0
45 55 65 75 85 95
AMBIENT TEMPERATURE (°C)
105
4605 F09
Figure 9. 5VIN to 16VOUT without Heatsink
125
4605 F08
Figure 7. 5VIN to 12VOUT without Heatsink
MAXIMUM LOAD CURRENT (A)
12
25
35
45 55 65 75 85 95
AMBIENT TEMPERATURE (°C)
105
4605 F10
Figure 10. 5VIN to 16VOUT with Heatsink
4605fa
17
LTM4605
TYPICAL APPLICATIONS
Power loss includes all external components
BGA Heat Sink
12
12
10
10
MAXIMUM LOAD CURRENT (A)
MAXIMUM LOAD CURRENT (A)
No Heat Sink
8
6
4
2
0
8
6
4
2
0
35
45
55
65
75
85
95
AMBIENT TEMPERATURE (°C)
20VIN TO 12VOUT WITH 0LFM
20VIN TO 12VOUT WITH 200LFM
20VIN TO 12VOUT WITH 400LFM
105
4605 F11
Figure 11. 20VIN to 12VOUT without Heatsink
35
45
55
65
75
85
95
AMBIENT TEMPERATURE (°C)
20VIN TO 12VOUT WITH 0LFM
20VIN TO 12VOUT WITH 200LFM
20VIN TO 12VOUT WITH 400LFM
105
4605 F12
Figure 12. 20VIN to 12VOUT with Heatsink
4605fa
18
LTM4605
APPLICATIONS INFORMATION
Table 4. 5V Output
DERATING CURVE
VIN (V)
POWER LOSS CURVE
AIR FLOW (LFM)
HEATSINK
θJA (°C/W)*
Figure 7, 9
12, 16
Figure 5
0
none
11.2
Figure 7, 9
12, 16
Figure 5
200
none
8.3
Figure 7, 9
12, 16
Figure 5
400
none
7.2
Figure 8, 10
12, 16
Figure 5
0
BGA Heatsink
10.7
Figure 8, 10
12, 16
Figure 5
200
BGA Heatsink
7.7
Figure 8, 10
12, 16
Figure 5
400
BGA Heatsink
6.6
VIN (V)
POWER LOSS CURVE
AIR FLOW (LFM)
HEATSINK
θJA (°C/W)*
Figure 11
20
Figure 6
0
none
8.2
Figure 11
20
Figure 6
200
none
5.8
Figure 11
20
Figure 6
400
none
5.3
Figure 12
20
Figure 6
0
BGA Heatsink
7.6
Figure 12
20
Figure 6
200
BGA Heatsink
5.3
Figure 12
20
Figure 6
400
BGA Heatsink
4.8
Table 5. 20V Input and 12V Output
DERATING CURVE
HEATSINK MANUFACTURER
PART NUMBER
PHONE NUMBER
Wakefield Engineering
LTN20069
603-635-2600
*The results of thermal resistance from junction to ambient θJA are based on the demo board of DC1198A. Thus, the maximum temperature on board is
treated as the junction temperature (which is in the μModule for most cases) and the power losses from all components are counted for calculations. It has
to be mentioned that poor board design may increase the θJA.
4605fa
19
LTM4605
APPLICATIONS INFORMATION
Layout Checklist/Example
• Use a separated SGND ground copper area for components connected to signal pins. Connect the SGND
to PGND underneath the unit.
The high integration of LTM4605 makes the PCB board
layout very simple and easy. However, to optimize its electrical and thermal performance, some layout considerations
are still necessary.
Figure 13. gives a good example of the recommended
layout.
• Use large PCB copper areas for high current path, including VIN, RSENSE, SW1, SW2, PGND and VOUT. It helps to
minimize the PCB conduction loss and thermal stress.
SW1
SW2
VIN
L1
• Place high frequency input and output ceramic capacitors next to the VIN, PGND and VOUT pins to minimize
high frequency noise
• Route SENSE– and SENSE+ leads together with minimum
PC trace spacing. Avoid sense lines passing through
noisy areas, such as switch nodes.
RSENSE
VOUT
• Place a dedicated power ground layer underneath the
unit.
CIN
COUT
• To minimize the via conduction loss and reduce module
thermal stress, use multiple vias for interconnection
between the top layer and other power layers
+
–
SGND
PGND
PGND
RSENSE
• Do not put vias directly on pads, unless the vias are
capped.
4605 F13
KELVIN CONNECTIONS TO RSENSE
Figure 13. Recommended PCB Layout
TYPICAL APPLICATIONS
VIN
12V TO 20V
CLOCK SYNC
10μF
35V
x2
PGOOD VIN
ON/OFF
RUN
COMP
PLLIN V
OUT
FCB
LTM4605
INTVCC
R1
1.5k
R3
1k
L1
3.3μH
100μF
25V
VOUT
12V
12A
SW1
SW2
PLLFLTR
C3
0.1μF
+
EXTVCC
RSENSE
STBYMD
SENSE+
SS
SENSE–
R2
8mΩ
SGND
PGND
VFB
RFB
7.15k
4605 TA02
Figure 14. Buck Mode Operation with 12V to 20V Input
4605fa
20
LTM4605
TYPICAL APPLICATIONS
VIN
4.5V TO 12V
CLOCK SYNC
4.7μF
35V
PGOOD VIN
ON/OFF
RUN
COMP
R1
1.5k
R3
1k
C3
0.1μF
PLLIN V
OUT
FCB
LTM4605
2Ω
INTVCC
SW1
PLLFLTR
SW2
EXTVCC
RSENSE
STBYMD
SENSE+
SS
SENSE–
L1
3.3μH
22μF
25V
x2
2200pF
+
330μF
25V
VOUT
12V
5A
OPTIONAL
FOR LOW
SWITCHING NOISE
R2
7mΩ
SGND
VFB
PGND
RFB
7.15k
4605 TA03
Figure 15. Boost Mode Operation with 4.5V to 12V Input
VIN
4.5V TO 20V
CLOCK SYNC
10μF
35V
x2
PGOOD VIN
ON/OFF
PLLIN V
OUT
RUN
COMP
FCB
LTM4605
R3
1k
SW2
PLLFLTR
C3
0.1μF
330μF
25V
VOUT
12V
5A
SW1
INTVCC
R1
1.5k
22μF
25V
x2
L1
3.3μH
+
EXTVCC
RSENSE
STBYMD
SENSE+
R2
7mΩ
SENSE–
SS
SGND
PGND
VFB
RFB
7.15k
4605 TA04
Figure 16. Wide Input Mode with 4.5V to 20V Input, 12V at 5A Output
4605fa
21
LTM4605
TYPICAL APPLICATIONS
VIN
4.5V TO 20V
CLOCK SYNC
10μF
35V
x2
ON/OFF
PGOOD VIN
PLLIN V
OUT
RUN
COMP
+
FCB
L1
2.5μH
LTM4605
INTVCC
SW1
R1
1.5k
PLLFLTR
SW2
EXTVCC
RSENSE
C3
R3
1k 0.1μF
STBYMD
SENSE+
SS
SENSE–
100μF
25V
2Ω
VOUT
5V
12A
2200pF
OPTIONAL
R2
8mΩ
SGND
VFB
PGND
RFB
19k
4605 TA05
Figure 17. 5V at 12A Design with Low Switching Noise (Optional)
VIN
4.5V TO 20V
CLOCK SYNC 0° PHASE
10μF
35V
R5
100k
PGOOD VIN
PLLIN V
OUT
RUN
FCB
LTM4605
COMP
R4
324k
LTC6908-1
V+
OUT1
GND
OUT2
SET
5.1V
RSENSE
EXTVCC
SENSE+
330μF
25V
R2
7mΩ
SENSE–
SS
C3
0.1μF
SGND
+
SW2
PLLFLTR
STBYMD
MOD
C2
22μF
x2
SW1
INTVCC
C1
0.1μF
L1
3.3μH
VOUT
12V
10A
PGND
VFB
RFB
3.57k
2-PHASE OSCILLATOR
CLOCK SYNC 180° PHASE
10μF
35V
PGOOD VIN
PLLIN V
OUT
FCB
RUN
LTM4605
COMP
L2
3.3μH
+
330μF
25V
SW1
INTVCC
SW2
PLLFLTR
RSENSE
EXTVCC
SENSE+
R3
7mΩ
STBYMD
SENSE–
SS
SGND
C4
22μF
x2
PGND
VFB
4605 TA06
Figure 18. Two-Phase Parallel, 12V at 10A Design
4605fa
22
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
6.9850
5.7150
4.4450
3.1750
1.9050
0.6350
0.0000
0.6350
1.9050
3.1750
4.4450
5.7150
6.9850
PACKAGE TOP VIEW
3.1750
3.1750
SUGGESTED PCB LAYOUT
TOP VIEW
1.9050
4
0.6350
0.0000
0.6350
PAD 1
CORNER
15
BSC
1.9050
aaa Z
6.9850
5.7150
4.4450
4.4450
5.7150
6.9850
X
15
BSC
Y
bbb Z
DETAIL B
2.72 – 2.92
DETAILS OF PAD #1 IDENTIFIER ARE OPTIONAL,
BUT MUST BE LOCATED WITHIN THE ZONE INDICATED.
THE PAD #1 IDENTIFIER MAY BE EITHER A MOLD OR
MARKED FEATURE
LAND DESIGNATION PER JESD MO-222, SPP-010
SYMBOL TOLERANCE
0.10
aaa
0.10
bbb
0.05
eee
6. THE TOTAL NUMBER OF PADS: 141
5. PRIMARY DATUM -Z- IS SEATING PLANE
4
3
2. ALL DIMENSIONS ARE IN MILLIMETERS
3
12
11
TRAY PIN 1
BEVEL
COMPONENT
PIN “A1”
PADS
SEE NOTES
1.27
BSC
13.97
BSC
0.12 – 0.28
NOTES:
1. DIMENSIONING AND TOLERANCING PER ASME Y14.5M-1994
DETAIL A
0.27 – 0.37
SUBSTRATE
eee S X Y
DETAIL B
0.630 ±0.025 SQ. 141x
aaa Z
2.45 – 2.55
MOLD
CAP
Z
(Reference LTC DWG # 05-08-1815 Rev A)
LGA Package
141-Lead (15mm × 15mm × 2.82mm)
10
7
6
5
LTMXXXXXX
μModule
PACKAGE BOTTOM VIEW
8
4
3
2
LGA 141 1007 REV A
1
DETAIL A
PACKAGE IN TRAY LOADING ORIENTATION
9
13.97
BSC
A
B
C
D
E
F
G
H
J
K
L
M
PAD 1
LTM4605
PACKAGE DESCRIPTION
4605fa
23
LTM4605
PACKAGE DESCRIPTION
Pin Assignment Table 6
(Arranged by Pin Number)
PIN NAME
PIN NAME
PIN NAME
PIN NAME
PIN NAME
PIN NAME
A1
PGND
C1
PGND
E1
VOUT
G1
VOUT
J1
SW1
L1
SW1
A2
PGND
C2
PGND
E2
VOUT
G2
VOUT
J2
SW1
L2
SW1
A3
PGND
C3
PGND
E3
PGND
G3
VOUT
J3
SW1
L3
SW1
A4
SENSE+
C4
PGND
E4
PGND
G4
VOUT
J4
SW1
L4
SW1
A5
SENSE–
C5
PGND
E5
PGND
G5
RSENSE
J5
RSENSE
L5
RSENSE
A6
SS
C6
PGND
E6
PGND
G6
RSENSE
J6
RSENSE
L6
RSENSE
A7
SGND
C7
PGND
E7
PGND
G7
RSENSE
J7
RSENSE
L7
SW2
A8
RUN
C8
PGND
E8
PGND
G8
RSENSE
J8
SW2
L8
SW2
A9
FCB
C9
PGND
E9
PGND
G9
RSENSE
J9
SW2
L9
SW2
A10 STBYMD C10 PGND
E10 PGND
G10 RSENSE
J10 VIN
L10 VIN
A11 PGND
C11 PGND
E11 PGND
G11 RSENSE
J11 VIN
L11 VIN
A12 PGND
C12 PGND
E12 PGND
G12 RSENSE
J12 VIN
B1
PGND
D1
PGND
F1
VOUT
H1
VOUT
K1
SW1
M1
B2
PGND
D2
PGND
F2
VOUT
H2
VOUT
K2
SW1
M2
SW1
B3
PGND
D3
PGND
F3
VOUT
H3
VOUT
K3
SW1
M3
SW1
B4
PGND
D4
PGND
F4
VOUT
H4
VOUT
K4
SW1
M4
SW1
RSENSE
L12 VIN
SW1
B5
PGOOD
D5
PGND
F5
INTVCC
H5
RSENSE
K5
RSENSE
M5
B6
VFB
D6
PGND
F6
EXTVCC
H6
RSENSE
K6
RSENSE
M6
RSENSE
B7
COMP
D7
PGND
F7
–
H7
RSENSE
K7
SW2
M7
SW2
B8
PLLFLTR D8
PGND
F8
–
H8
RSENSE
K8
SW2
M8
SW2
B9
PLLIN
PGND
F9
–
H9
RSENSE
K9
SW2
M9
SW2
D9
B10 PGND
D10 PGND
F10 RSENSE
H10 RSENSE
K10 VIN
B11 PGND
D11 PGND
F11 RSENSE
H11 RSENSE
K11 VIN
M10 VIN
M11 VIN
B12 PGND
D12 PGND
F12 RSENSE
H12 RSENSE
K12 VIN
M12 VIN
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC2900
Quad Supply Monitor with Adjustable Reset Timer
Monitors Four Supplies; Adjustable Reset Timer
LTC2923
Power Supply Tracking Controller
Tracks Both Up and Down; Power Supply Sequencing
LTC3780
36V Buck-Boost Controller
Synchronous Operation, Single Inductor
LTC3785
10V Buck-Boost Controller
Synchronous Operation, No RSENSE™, 2.7V ≤ VIN ≤ 10V, 2.7V ≤ VOUT ≤ 10V
LT3825/LT3837
Synchronous Isolated Flyback Controllers
No Optocoupler Required; 3.3V, 12A Output; Simple Design
LTM4600
10A DC/DC μModule
Basic 10A DC/DC μModule
LTM4601/
LTM4601A
12A DC/DC μModule with PLL, Output Tracking/
Margining and Remote Sensing
Synchronizable, PolyPhase Operation to 48A, LTM4601-1 Version has no
Remote Sensing
LTM4602
6A DC/DC μModule
Pin Compatible with the LTM4600
LTM4603
6A DC/DC μModule with PLL and Output Tracking/
Margining and Remote Sensing
Synchronizable, PolyPhase Operation, LTM4603-1 Version has no Remote
Sensing, Pin Compatible with the LTM4601
LTM4604
4A Low Voltage DC/DC μModule
2.375 ≤ VIN ≤ 5V, 0.8V ≤ VOUT ≤ 5V, 9mm × 15mm × 2.3mm Package
No RSENSE is a Trademark of Linear Technology Corporation.
4605fa
24 Linear Technology Corporation
LT 0108 REV A • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507 ● www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2007
Similar pages