LTM8056
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For more information www.linear.com/LTM8056
TYPICAL APPLICATION
FEATURES DESCRIPTION
58VIN, 48VOUT Buck-Boost
µModule Regulator
The LT M
®
8056 is a 58VIN, buck-boost µModule
®
(micromodule) regulator. Included in the package are the
switching controller, power switches, inductor and support
components. A resistor to set the switching frequency, a
resistor divider to set the output voltage, and input and
output capacitors are all that are needed to complete the
design. Other features such as input and output average
current regulation may be implemented with just a few
components. The LTM8056 operates over an input volt-
age range of 5V to 58V, and can regulate output voltages
between 1.2V and 48V. The SYNC input and CLKOUT
output allow easy synchronization.
The LTM8056 is housed in a compact overmolded ball
grid array (BGA) package suitable for automated assembly
by standard surface mount equipment. The LTM8056 is
available with SnPB or RoHS compliant terminal finish.
Buck-Boost Selection Table
LTM8054 LTM8055 LTM8056
VIN (Operation) 36 36 58
VIN Abs Max 40 40 60
VOUT Abs Max 40 40 60
IOUT (Peak)
24VIN, 12VOUT
5.4 8.5 5.5
Package 15 × 11.25mm ×
3.42mm BGA 15 × 15mm × 4.92mm BGA
Pin and Function Compatible
24VOUT from 7VIN to 58VIN Buck-Boost Regulator
APPLICATIONS
n Complete Buck-Boost Switch Mode Power Supply
n Wide Input Voltage Range: 5V to 58V
n 12V/1.7A Output from 6VIN
n 12V/3.4A Output from 12VIN
n 12V/5.4A Output from 24VIN
n Up to 96% Efficient
n Adjustable Input and Output Average Current Limits
n Input and Output Current Monitors
n Parallelable for Increased Output Current
n Wide Output Voltage Range: 1.2V to 48V
n Selectable Switching Frequency: 100kHz to 800kHz
n Synchronization from 200kHz to 700kHz
n 15mm × 15mm × 4.92mm BGA Package
n High Power Battery-Operated Devices
n Industrial Control
n Solar Powered Voltage Regulator
n Solar Powered Battery Charging
L, LT , LT C , LT M , Linear Technology, the Linear logo, µModule and Burst Mode are registered
trademarks of Linear Technology Corporation. All other trademarks are the property of their
respective owners.
Max Output Current and Efficiency vs VIN
VIN
SVIN
IIN
LTM8056
IOUT
VOUT
CLKOUT
IINMON
IOUTMON
FB
RUN
CTL
SS
SYNC
COMP
RT
5.23k
8056 TA01a
22µF
25V
33µF
35V
VOUT
24V
2.2µF
100V
×3
VIN
7V TO 58V
43.2k
fSW = 525kHz
100k
GNDMODELL
VIN (V)
0
EFFICIENCY AT MAX OUTPUT CURRENT (%)
MAX OUTPUT CURRENT (A)
95
93
92
94
91
90
7
6
4
2
5
3
1
0
8056 TA01b
5020 3010 40
EFFICIENCY
MAX OUTPUT CURRENT
LTM8056
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8056fa
For more information www.linear.com/LTM8056
PIN CONFIGURATIONABSOLUTE MAXIMUM RATINGS
VIN, SVIN, VOUT, RUN, IIN, IOUT Voltage .....................60V
FB, SYNC, CTL, MODE Voltage ...................................6V
IINMON, IOUTMON Voltage .............................................6V
LL Voltage .................................................................15V
Maximum Junction Temperature (Notes 2, 3) ....... 125°C
Storage Temperature.............................. –55°C to 125°C
Peak Solder Reflow Body Temperature ................. 245°C
(Note 1)
BANK 2
VOUT
A
IOUT LL
CLKOUT
RT FB SS
MODE SYNC
COMP
CTL
1
11
10
9
8
7
6
5
4
3
2
KJ LHGFEDCB
BGA PACKAGE
121-LEAD (15mm × 15mm × 4.92mm)
BANK 1
GND
BANK 3
VIN
TOP VIEW
SVIN
IIN
RUN
IINMON
IOUTMON
GND
TJMAX = 125°C, θJA = 16.4°C/W, θJCbottom = 5.35°C/W, θJCtop = 15.3°C/W, θJB = 5.9°C/W,
WEIGHT = 2.8g, θ VALUES DETERMINED PER JEDEC JESD51-9, 51-12
ORDER INFORMATION
PART NUMBER BALL FINISH PART MARKING* PACKAGE
TYPE
MSL
RATING
TEMPERATURE RANGE
(Note 2)
DEVICE FINISH CODE
LTM8056EY#PBF SAC305 (RoHS) LTM8056Y e1 BGA 3 –40°C to 125°C
LTM8056IY#PBF SAC305 (RoHS) LTM8056Y e1 BGA 3 –40°C to 125°C
LTM8056IY SnPb (63/37) LTM8056Y e0 BGA 3 –40°C to 125°C
LTM8056MPY#PBF SAC305 (RoHS) LTM8056Y e1 BGA 3 –55°C to 125°C
LTM8056MPY SnPb (63/37) LTM8056Y e0 BGA 3 –55°C to 125°C
Consult Marketing for parts specified with wider operating temperature
ranges.
*Device temperature grade is indicated by a label on the shipping
container. Pad or ball finish code is per IPC/JEDEC J-STD-609.
• Terminal Finish Part Marking:
www.linear.com/leadfree
• Recommended LGA and BGA PCB Assembly and Manufacturing
Procedures:
www.linear.com/umodule/pcbassembly
• LGA and BGA Package and Tray Drawings:
www.linear.com/packaging
http://www.linear.com/product/LTM8056#orderinfo
LTM8056
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For more information www.linear.com/LTM8056
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. RUN = 1.5V unless otherwise noted. (Note 2)
PARAMETER CONDITIONS MIN TYP MAX UNITS
Minimum Input Voltage VIN = SVIN l5.0 V
Output DC Voltage FB = VOUT Through 100k
IOUT = 0.1A, RFB = 100k/2.55k
1.2
48
V
V
Output DC Current VIN = 6V, VOUT = 12V
VIN = 48V, VOUT = 12V
1.7
4
A
A
Quiescent Current Into VIN (Tied to SVIN) RUN = 0.3V (Disabled)
No Load, MODE = 0.3V (DCM)
No Load, MODE = 1.5V (FCM)
0.1
8
45
1
30
100
µA
mA
mA
Output Voltage Line Regulation 5V < VIN < 58V, IOUT = 1A 0.5 %
Output Voltage Load Regulation VIN = 12V, 0.1A < IOUT < 3.5A 0.5 %
Output RMS Voltage Ripple VIN = 24V, IOUT = 3A 25 mV
Switching Frequency RT = 453k
RT = 24.9k
100
800
kHz
kHz
Voltage at FB Pin
l
1.188
1.176
1.212
1.220
V
V
RUN Falling Threshold LTM8056 Stops Switching l1.15 1.25 V
RUN Hysteresis LTM8056 Starts Switching 25 mV
RUN Low Threshold LTM8056 Disabled 0.3 V
RUN Pin Current RUN = 1V
RUN = 1.6V
235
100
µA
nA
IIN Bias Current 90 µA
Input Current Sense Threshold (IIN-VIN)l44 56 mV
IOUT Bias Current 20 µA
Output Current Sense Threshold (VOUT-IOUT) VCTL = Open
l
54.5
53
61.5
63
mV
mV
IINMON Voltage LTM8056 in Input Current Limit 0.96 1.04 V
IOUTMON Voltage LTM8056 in Output Current Limit 1.14 1.26 V
CTL Input Bias Current VCTL = 0V 22 µA
SS Pin Current VSS = 0V 35 µA
CLKOUT Output High 10k to GND 4 V
CLKOUT Output Low 10k to 5V 0.7 V
SYNC Input Low Threshold 0.3 V
SYNC Input High Threshold 1.5 V
SYNC Bias Current SYNC = 1V 11 µA
MODE Input Low Threshold 0.3 V
MODE Input High Threshold 1.5 V
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 LTM8056E is guaranteed to meet performance specifications
from 0°C to 125°C internal. Specifications over the full –40°C to
125°C internal operating temperature range are assured by design,
characterization and correlation with statistical process controls. The
LTM8056I is guaranteed to meet specifications over the full –40°C
to 125°C internal operating temperature range. The LTM8056MP is
guaranteed to meet specifications over the full –55°C to 125°C internal
operating temperature range. Note that the maximum internal temperature
is determined by specific operating conditions in conjunction with board
layout, the rated package thermal resistance and other environmental
factors.
Note 3: The LTM8056 contains overtemperature protection that is
intended to protect the device during momentary overload conditions. The
internal temperature exceeds the maximum operating junction temperature
when the overtemperature protection is active. Continuous operation
above the specified maximum operating junction temperature may impair
device reliability.
LTM8056
4
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For more information www.linear.com/LTM8056
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Output Current
(12VOUT)
Efficiency vs Output Current
(18VOUT)
Efficiency vs Output Current
(24VOUT)
Efficiency vs Output Current
(36VOUT)
Efficiency vs Output Current
(48VOUT)
Input Current vs Output Current
(3.3VOUT)
Efficiency vs Output Current
(3.3VOUT)
Efficiency vs Output Current
(5VOUT)
Efficiency vs Output Current
(8VOUT)
TA = 25°C, unless otherwise noted.
OUTPUT CURRENT (A)
0
EFFICIENCY (%)
100
80
60
40
8056 G01
62 4
5VIN
12VIN
24VIN
OUTPUT CURRENT (A)
0
EFFICIENCY (%)
100
80
60
40
8056 G02
62 4
5VIN
12VIN
22VIN
OUTPUT CURRENT (A)
0
EFFICIENCY (%)
100
80
60
40
8056 G03
62 4
5VIN
12VIN
24VIN
OUTPUT CURRENT (A)
0
EFFICIENCY (%)
100
80
90
70
8056 G04
2 4 6
5VIN
12VIN
24VIN
36VIN
OUTPUT CURRENT (A)
0
EFFICIENCY (%)
100
90
80
70
8056 G05
2 4 6
6VIN
12VIN
24VIN
48VIN
OUTPUT CURRENT (A)
EFFICIENCY (%)
100
90
85
80
95
75
8056 G06
40 2 6
7VIN
12VIN
24VIN
36VIN
48VIN
OUTPUT CURRENT (A)
EFFICIENCY (%)
100
95
90
85
8056 G07
40 2 6
9VIN
12VIN
24VIN
36VIN
48VIN
OUTPUT CURRENT (A)
INPUT CURRENT (A)
4
3
2
1
0
8056 G09
40 2 6
5VIN
12VIN
24VIN
OUTPUT CURRENT (A)
EFFICIENCY (%)
100
95
90
85
8056 G08
20 1 43
13VIN
24VIN
36VIN
48VIN
LTM8056
5
8056fa
For more information www.linear.com/LTM8056
TYPICAL PERFORMANCE CHARACTERISTICS
Input Current vs Output Current
(18VOUT)
Input Current vs Output Current
(24VOUT)
Input Current vs Output Current
(36VOUT)
Input Current vs Output Current
(48VOUT) Maximum Output Current vs VIN Maximum Output Current vs VIN
Input Current vs Output Current
(5VOUT)
Input Current vs Output Current
(8VOUT)
Input Current vs Output Current
(12VOUT)
TA = 25°C, unless otherwise noted.
OUTPUT CURRENT (A)
INPUT CURRENT (A)
4
3
2
1
0
8056 G10
40 2 6
5VIN
12VIN
22VIN
OUTPUT CURRENT (A)
INPUT CURRENT (A)
5
4
3
2
1
0
8056 G11
40 2 6
5VIN
12VIN
24VIN
OUTPUT CURRENT (A)
INPUT CURRENT (A)
4
3
2
1
0
8056 G12
60 2 4
5VIN
12VIN
24VIN
36VIN
OUTPUT CURRENT (A)
INPUT CURRENT (A)
5
4
3
2
1
0
8056 G13
60 2 4
6VIN
12VIN
24VIN
48VIN
OUTPUT CURRENT (A)
INPUT CURRENT (A)
5
4
3
2
1
0
8056 G14
60 2 4
7VIN
12VIN
24VIN
36VIN
48VIN
OUTPUT CURRENT (A)
INPUT CURRENT (A)
5
4
3
2
1
0
8056 G15
4 60 2
9VIN
12VIN
24VIN
36VIN
48VIN
OUTPUT CURRENT (A)
INPUT CURRENT (A)
4
3
2
1
0
8056 G16
2.5 3.0 3.50 0.5 1.0 1.5 2.0
13VIN
24VIN
36VIN
48VIN
VIN (V)
OUTPUT CURRENT (A)
6
5
4
3
2
8056 G17
20 300 10
3.3VOUT
5VOUT
8VOUT
VIN (V)
OUTPUT CURRENT (A)
6
5
4
0
3
2
1
8056 G18
30 40 500
10
20
12VOUT
18VOUT
24VOUT
LTM8056
6
8056fa
For more information www.linear.com/LTM8056
TYPICAL PERFORMANCE CHARACTERISTICS
Temperature Rise vs Output
Current (8VOUT)
Temperature Rise vs Output
Current (12VOUT)
Temperature Rise vs Output
Current (18VOUT)
Temperature Rise vs Output
Current (24VOUT)
Temperature Rise vs Output
Current (36VOUT)
Temperature Rise vs Output
Current (48VOUT)
Maximum Output Current vs VIN
Temperature Rise vs Output
Current (3.3VOUT)
Temperature Rise vs Output
Current (5VOUT)
TA = 25°C, unless otherwise noted.
VIN (V)
OUTPUT CURRENT (A)
6
4
2
0
8056 G19
20 30 40 500 10
36VOUT
48VOUT
OUTPUT CURRENT (A)
TEMPERATURE RISE (°C)
80
60
40
20
0
8056 G20
60 2 4
5VIN
12VIN
24VIN
OUTPUT CURRENT (A)
TEMPERATURE RISE (°C)
100
80
60
40
20
0
8056 G21
60 2 4
5VIN
12VIN
22VIN
OUTPUT CURRENT (A)
TEMPERATURE RISE (°C)
100
80
60
40
20
0
8056 G22
4 60 2
5VIN
12VIN
24VIN
OUTPUT CURRENT (A)
TEMPERATURE RISE (°C)
100
80
60
40
20
0
8056 G23
4 60 2
5VIN
12VIN
24VIN
36VIN
OUTPUT CURRENT (A)
TEMPERATURE RISE (°C)
100
80
60
40
20
0
8056 G24
60 2 4
6VIN
12VIN
24VIN
48VIN
OUTPUT CURRENT (A)
TEMPERATURE RISE (°C)
100
80
60
40
20
0
8056 G25
60 2 4
7VIN
12VIN
24VIN
36VIN
48VIN
OUTPUT CURRENT (A)
TEMPERATURE RISE (°C)
100
80
60
40
20
0
8056 G26
60 2 4
9VIN
12VIN
24VIN
36VIN
48VIN
OUTPUT CURRENT (A)
TEMPERATURE RISE (°C)
100
80
60
40
20
0
8056 G27
40 1 2 3
13VIN
24VIN
36VIN
48VIN
LTM8056
7
8056fa
For more information www.linear.com/LTM8056
TYPICAL PERFORMANCE CHARACTERISTICS
Maximum Output Current vs CTL
Voltage DC2154A Demo Board,48VIN
Soft-Start Waveforms for Various
CSS Values 24VIN, 3A Resistive
Load, DC2154A Demo Board
Output Ripple, Stock DC2154A
Demo Board, 24VOUT
TA = 25°C, unless otherwise noted.
PIN FUNCTIONS
GND (Bank 1, Pin L1): Tie these GND pins to a local ground
plane below the LTM8056 and the circuit components.
In most applications, the bulk of the heat flow out of the
LTM8056 is through these pads, so the printed circuit
design has a large impact on the thermal performance of
the part. See the PCB Layout and Thermal Considerations
sections for more details. Return the RFB1/RFB2 feedback
divider to this net.
VOUT (Bank 2): Power Output Pins. Apply output filter
capacitors between these pins and GND pins.
VIN (Bank 3): Input Power. The VIN pin supplies current to
the LTM8056’s internal power switches and to one terminal
of the optional input current sense resistor. This pin must
be locally bypassed with an external, low ESR capacitor;
see Table 1 for recommended values.
IOUT (Pin D1): Output Current Sense. Tie this pin to the
output current sense resistor. The output average current
sense threshold is 58mV, so the LTM8056 will regulate
the output current to 58mV/RSENSE, where RSENSE is the
value of the output current sense resistor in ohms. The
load is powered through the sense resistor connected at
this pin. Tie this pin to VOUT if no output current sense
resistor is used. Keep this pin within ±0.5V of VOUT under
all conditions.
LL (Pin F1): Light Load Indicator. This open drain pin
indicates that the output current, as sensed through the
resistor connected between VOUT and IOUT, is approxi-
mately equivalent to 6mV or less. Its state is meaningful
only if a current sense resistor is applied between VOUT
and IOUT. This is useful to change the switching behavior
of the LTM8056 in light load conditions.
SVIN (Pins F10, F11): Controller Power Input. Apply a
separate voltage above 5V if the LTM8056 is required to
operate when the main power input (VIN) is below 5V.
Bypass these pins with a high quality, low ESR capacitor.
If a separate supply is not used, connect these pins to VIN.
CLKOUT (Pin G1): Clock Output. Use this pin as a clock
source when synchronizing other devices to the switch-
ing frequency of the LTM8056. When this function is not
used, leave this pin open.
MODE (Pin G2): Switching Mode Input. The LTM8056
operates in forced continuous mode when MODE is
open, and can operate in discontinuous switching mode
when MODE is low. In discontinuous switching mode,
the LTM8056 will block reverse inductor current. This pin
is normally left open or tied to LL. This pin may be tied
to GND for the purpose of blocking reverse current if no
output sense resistor is used.
CTL VOLTAGE (V)
OUTPUT CURRENT (A)
4
3
2
1
0
8056 G28
1.40 0.4 0.7 1.1
VOUT
5V/DIV
8056 G29
500µs/DIV
CSS = 22nF
CSS = 100nF
CSS = 220nF
24VIN, 3A LOAD
(BUCK-B00ST),
100mV/DIV
48VIN, 3A LOAD
(Buck),
100mV/DIV
12VIN, 1.5A LOAD
(B00ST),
100mV/DIV
MEASURED ACROSS C17 ON DC2154A WITH HP461
AMPLIFIER, 150MHz BANDWIDTH
8056 G30
1µs/DIV
LTM8056
8
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For more information www.linear.com/LTM8056
PIN FUNCTIONS
RT (Pin H1): Timing Resistor. The RT pin is used to program
the switching frequency of the LTM8056 by connecting a
resistor from this pin to ground. The range of oscillation is
100kHz to 800kHz. The Applications Information section of
the data sheet includes a table to determine the resistance
value based on the desired switching frequency. Minimize
capacitance at this pin. A resistor to ground must be ap-
plied under all circumstances.
SYNC (Pin H2): External Synchronization Input. The SYNC
pin has an internal pull-down resistor. See the Synchroni-
zation section in Applications Information for details. Tie
this pin to GND when not used.
FB (Pin J1): Output Voltage Feedback. The LTM8056
regulates the FB pin to 1.2V. Connect the FB pin to a
resistive divider between the output and GND to set the
output voltage. See Table 1 for recommended FB divider
resistor values.
COMP (Pin J2): Compensation Pin. The LTM8056 is
equipped with internal compensation that works well with
most applications. In some cases, the performance of the
LTM8056 can be enhanced by modifying the control loop
compensation by applying a capacitor or RC network to
this pin.
SS (Pin K1): Soft-Start. Connect a capacitor from this pin
to GND to increase the soft-start time. Soft-start reduces
the input power source’s surge current by gradually in-
creasing the controller’s current limit. Larger values of the
soft-start capacitor result in longer soft-start times. If no
soft-start is required, leave this pin open.
CTL (Pin K2): Current Sense Adjustment. Apply a voltage
below 1.2V to reduce the current limit threshold of IOUT.
Drive CTL to less than about 50mV to stop switching. The
CTL pin has an internal pull-up resistor to 2V. If not used,
leave this pin open.
IOUTMON (Pin L2): Output Current Monitor. This pin pro-
duces a voltage that is proportional to the voltage between
VOUT and IOUT. IOUTMON will equal 1.2V when VOUT – IOUT
= 58mV. This feature is generally useful only if a current
sense resistor is applied between VOUT and IOUT. This is
a high impedance output. Use a buffer to drive a load.
IINMON (Pin L3): Input Current Monitor. This pin produces
a voltage that is proportional to the voltage between IIN
and VIN. IINMON will equal 1V when IIN-VIN = 50mV. This
feature is generally useful only if a current sense resistor
is applied between VIN and IIN.
RUN (Pin L4): LTM8056 Enable. Raise the RUN pin voltage
above 1.2V for normal operation. Above 1.2V (typical), but
below 6V, the RUN pin input bias current is less than 1μA.
Below 1.2V and above 0.3V, the RUN pin sinks 3μA so
the user can define the hysteresis with the external resis-
tor selection. This will also reset the soft-start function.
If RUN is 0.3V or less, the LTM8056 is disabled and the
SVIN quiescent current is below 1μA.
IIN (Pin L9): Input Current Sense. Tie this pin to the input
current sense resistor. The input average current sense
threshold is 50mV, so the LTM8056 will regulate the input
current to 50mV/RSENSE, where RSENSE is the value of the
input current sense resistor in ohms. Tie to VIN when not
used. Keep this pin within ±0.5V of VIN under all conditions.
LTM8056
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For more information www.linear.com/LTM8056
OPERATION
The LTM8056 is a standalone nonisolated buck-boost
switching DC/DC power supply. The buck-boost topol-
ogy allows the LTM8056 to regulate its output voltage
for input voltages both above and below the magnitude
of the output, and the maximum output current depends
upon the input voltage. Higher input voltages yield higher
maximum output current.
This converter provides a precisely regulated output volt-
age programmable via an external resistor divider from
1.2V to 48V. The input voltage range is 5V to 58V, but the
LTM8056 may be operated at lower input voltages if SVIN
is powered by a voltage source above 5V. A simplified
block diagram is given on the previous page.
The LTM8056 contains a current mode controller, power
switching elements, power inductor and a modest amount
of input and output capacitance. The LTM8056 is a fixed
frequency PWM regulator. The switching frequency is set
by connecting the appropriate resistor value from the RT
pin to GND.
The output voltage of the LTM8056 is set by connecting the
FB pin to a resistor divider between the output and GND.
In addition to regulating its output voltage, the LTM8056
is equipped with average current control loops for both the
input and output. Add a current sense resistor between IIN
and VIN to limit the input current below some maximum
value. The IINMON pin reflects the current flowing though
the sense resistor between IIN and VIN.
A current sense resistor between VOUT and IOUT allows
the LTM8056 to accurately regulate its output current to
a maximum value set by the value of the sense resistor.
In general, the LTM8056 should be used with an output
sense resistor to limit the maximum output current, as
buck-boost regulators are capable of delivering large cur-
rents when the output voltage is lower than the input, if
demanded.
Furthermore, while the LTM8056 does not require an
output sense resistor to operate, it uses information from
the sense resistor to optimize its performance. If an out-
put sense resistor is not used, the efficiency or output
ripple may degrade, especially if the current through the
integrated inductor is discontinuous. In some cases, an
output sense resistor is required to adequately protect the
LTM8056 against output overload or short-circuit.
A voltage less than 1.2V applied to the CTL pin reduces
the maximum output current if an output current sense
resistor is used. Drive CTL to less than about 50mV to stop
switching. The current flowing through the sense resistor
is reflected by the output voltage of the IOUTMON pin.
Driving the SYNC pin will synchronize the LTM8056 to an
external clock source. The CLKOUT pin sources a signal
that is the same frequency but approximately 180° out of
phase with the internal oscillator.
If more output current is required than a single LTM8056
can provide, multiple devices may be operated in parallel.
Refer to the Parallel Operation section of Applications
Information for more details.
An internal regulator provides power to the control circuitry
and the gate driver to the power MOSFETs. This internal
regulator draws power from the SVIN pin. The RUN pin is
used to place the LTM8056 in shutdown, disconnecting
the output and reducing the input current to less than 1μA.
The LTM8056 is equipped with a thermal shutdown that
inhibits power switching at high junction temperatures.
The activation threshold of this function is above 125°C
to avoid interfering with normal operation, so prolonged
or repetitive operation under a condition in which the
thermal shutdown activates may damage or impair the
reliability of the device.
LTM8056
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For more information www.linear.com/LTM8056
APPLICATIONS INFORMATION
For most applications, the design process is straight for-
ward, summarized as follows:
1. Look at Table 1 and find the row that has the desired
input range and output voltage.
2. Apply the recommended CIN, COUT, RFB1/RFB2 and RT
values.
3. Apply the output sense resistor to set the output current
limit. The output current is limited to 58mV/RSENSE,
where RSENSE is the value of the output current sense
resistor in ohms.
While these component combinations have been tested for
proper operation, it is incumbent upon the user to verify
proper operation over the intended system’s line, load and
environmental conditions. Bear in mind that the maximum
output current is limited by junction temperature, the rela-
tionship between the input and output voltage magnitude
and other factors. Please refer to the graphs in the Typical
Performance Characteristics section for guidance.
The maximum frequency (and attendant RT value) at
which the LTM8056 should be allowed to switch is given
in Table 1 in the fMAX column, while the recommended
frequency (and RT value) for optimal efficiency over the
given input condition is given in the fOPTIMAL column.
There are additional conditions that must be satisfied if
the synchronization function is used. Please refer to the
Synchronization section for details.
Note that Table 1 calls out both ceramic and electrolytic
output capacitors. Both of the capacitors called out in
the table must be applied to the output. The electrolytic
capacitors in Table 1 are described by voltage rating,
value and ESR. The voltage rating of the capacitor may
be increased if the application requires a higher voltage
stress derating. The LTM8056 can tolerate variation
in the ESR; other capacitors with different ESR may
be used, but the user must verify proper operation
over line, load and environmental conditions. Table 2
gives the description and part numbers of electrolytic
capacitors used in the LTM8056 development testing and
design validation.
Table 1. Recommended Component Values and Configuration (TA = 25°C)
VIN RANGE VOUT CIN COUT RFB1/RFB2 fOPTIMAL (kHz) RT(OPTIMAL) fMAX (kHz) RT(MAX)
5V to 24V 3.3V 2 × 4.7µF, 50V, 0805 22µF, 6.3V, X5R, 0805
100µF, 6V, 75mΩ, Electrolytic
100k/56.2k 650 31.6k 800 24.9k
5V to 22V 5V 2 × 4.7µF, 50V, 0805 22µF, 6.3V, X5R, 0805
100µF, 6V, 75mΩ, Electrolytic
100k/31.6k 450 53.6k 800 24.9k
5V to 28V 8V 2 × 4.7µF, 50V, 0805 22µF, 10V, X7R, 1206
100µF, 16V, 100mΩ, Electrolytic
100k/17.4k 500 45.3k 800 24.9k
5V to 41V 12V 2 × 4.7µF, 50V, 0805 22µF, 25V, X5R, 0805
68µF, 16V, 200mΩ, Electrolytic
100k/11k 650 31.6k 800 24.9k
5.8V to 58V 18V 3 × 2.2µF, 100V, 1206 22µF, 25V, X5R, 0805
47µF, 25V, 900mΩ, Electrolytic
100k/6.98k 650 31.6k 800 24.9k
7V to 58V 24V 3 × 2.2µF, 100V, 1206 22µF, 25V, X5R, 0805
33µF, 35V 300mΩ, Electrolytic
100k/5.23k 525 43.2k 800 24.9k
8.5V to 58V 36V 3 × 2.2µF, 100V, 1206 10µF, 50V, X5R, 1206
10µF, 50V 120mΩ, Electrolytic
100k/3.40k 500 45.3k 800 24.9k
12.5V to 58V 48V 3 × 2.2µF, 100V, 1206 10µF, 50V, X5R, 1206
10µF, 63V 120mΩ, Electrolytic
100k/2.55k 475 49.9k 800 24.9k
Notes: An input bulk capacitor is required. The output capacitance uses a combination of a ceramic and electrolytic in parallel. Other combinations of
resistor values for the RFB network are acceptable.
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APPLICATIONS INFORMATION
Capacitor Selection Considerations
The CIN and COUT capacitor values in Table 1 are the
minimum recommended values for the associated oper-
ating conditions. Applying capacitor values below those
indicated in Table 1 is not recommended, and may result
in undesirable operation. Using larger values is generally
acceptable, and can yield improved dynamic response, if
it is necessary. Again, it is incumbent upon the user to
verify proper operation over the intended system’s line,
load and environmental conditions.
Ceramic capacitors are small, robust and have very low
ESR. However, not all ceramic capacitors are suitable.
X5R and X7R types are stable over temperature and ap-
plied voltage and give dependable service. Other types,
including Y5V and Z5U have very large temperature and
voltage coefficients of capacitance. In an application cir-
cuit they may have only a small fraction of their nominal
capacitance resulting in much higher output voltage ripple
than expected.
A final precaution regarding ceramic capacitors concerns
the maximum input voltage rating of the LTM8056. A
ceramic input capacitor combined with trace or cable
inductance forms a high Q (underdamped) tank circuit.
If the LTM8056 circuit is plugged into a live supply, the
input voltage can ring to twice its nominal value, possi-
bly exceeding the device’s rating. This situation is easily
avoided; see the Hot-Plugging Safely section.
Frequency Selection
The LTM8056 uses a constant frequency PWM architec-
ture that can be programmed to switch from 100kHz to
800kHz by tying a resistor from the RT pin to ground.
Table 3 provides a list of RT resistor values and their re-
sultant frequencies.
Table 3. Switching Frequency vs RT Value
FREQUENCY RT VALUE (kΩ)
100 453
200 147
300 84.5
400 59
500 45.3
600 36.5
700 29.4
800 24.9
An external resistor within the range stated in Table 3
from RT to GND is required. Even when synchronizing to
an external clock. When synchronizing the switching of
the LTM8056 to an external signal source, the frequency
range is 200kHz to 700kHz.
Operating Frequency Trade-Offs
It is recommended that the user apply the optimal RT
value given in Table 1 for the input and output operating
condition. System level or other considerations, however,
may necessitate another operating frequency. While the
LTM8056 is flexible enough to accommodate a wide range
of operating frequencies, a haphazardly chosen one may
result in undesirable operation under certain operating or
fault conditions. A frequency that is too high can reduce
efficiency, generate excessive heat or even damage the
Table 2. Electrolytic Caps Used in LTM8056 Testing
DESCRIPTION MANUFACTURER PART NUMBER
100µF, 6V, 75mΩ, Tantalum C Case AVX TPSC107M006R0075
100µF, 16V, 100mΩ, Tantalum Y Case AVX TPSY107M016R0100
68µF, 16V, 200mΩ, Tantalum C Case AVX TPSC686M016R0200
47µF, 25V, 900mΩ, Tantalum D Case AVX TAJD476M025R
33µF, 35V, 300mΩ, Tantalum D Case AVX TPSD336M035R0300
10µF, 50V, 120mΩ, Aluminum 6.3 × 6mm case Suncon 50HVP10M
10µF, 63V, 120mΩ, Aluminum 6.3 × 5.8mm case Panasonic EEHZA1J100P
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APPLICATIONS INFORMATION
LTM8056 if the output is overloaded or short circuited.
A frequency that is too low can result in a final design
that has too much output ripple or too large of an output
capacitor or is even unstable.
Parallel Operation
Tw o or more LTM8056s may be combined to provide
increased output current by configuring them as a mas-
ter and a slave, as shown in Figure 1. Each LTM8056 is
equipped with an IOUTMON and a CTL pin. The IOUTMON
pin’s 0V to 1.2V signal reflects the current passing through
the output sense resistor, while a voltage less than 1.2V
applied to the CTL pin will limit the current passing through
the output sense resistor. By applying the voltage of the
master’s IOUTMON pin to the slave’s CTL pin, the two units
will source the same current to the load, assuming each
LTM8056 output current sense resistor is the same value.
2. Apply a FB resistor network to the individual slaves
so that the resulting output is higher than the desired
output voltage.
3. Apply the appropriate output current sense resistors
between VOUT and IOUT. If the same value is used for the
master and slave units, they will share current equally.
4. Connect the master IOUTMON to the slaves’ CTL pin
through a unity gain buffer. The unity gain buffer is
required to isolate the output impedance of the LTM8056
from the integrated pull-up on the CTL pins.
5. Tie the outputs together.
Note that this configuration does not require the inputs to
be tied together, making it simple to power a single heavy
load from multiple input sources. Ensure that each input
power source has sufficient voltage and current sourcing
capability to provide the necessary power. Please refer
to the Maximum Output Current vs VIN and Input Current
vs Output Current curves in the Typical Performance
Characteristics section for guidance.
Paralleled LTM8056s should normally be allowed to switch
in discontinuous mode enabled to prevent current from
flowing from the output of one unit into another; that is,
the MODE pin should be tied to LL. In some cases, operat-
ing the master in forced continuous (MODE open) and the
slaves in discontinuous mode (MODE = LL) is desirable.
If so, current from the output can flow into the master’s
input. Please refer to Input Precaution in this section for
a discussion of this behavior.
Minimum Input Voltage and RUN
The LTM8056 needs a minimum of 5V for proper opera-
tion, but system parameters may dictate that the device
operate only above some higher input voltage. For ex-
ample, a LTM8056 may be used to produce 12VOUT, but
the input power source may not be budgeted to provide
enough current if the input supply voltage is below 8V.
The RUN pin has a typical falling voltage threshold of
1.2V and a typical hysteresis of 25mV. In addition, the
pin sinks 3µA below the RUN threshold. Based upon the
Figure 1. Tw o or More LTM8056s May Be Connected in a
Master/Slave Configuration for Increased Output Current
IOUT
MASTER
IOUTMON
OUTPUT CURRENT
SENSE RESISTOR
TO LOAD
VOUT
IOUT
CTL
SLAVE
VOUT
UNITY GAIN
BUFFER
8056 F01
OUTPUT CURRENT
SENSE RESISTOR
The design of a master-slave configuration is straight-
forward:
1. Apply the FB resistor network to the master, choosing
the proper values for the desired output voltage. Sug-
gested values for popular output voltages are provided
in Table 1.
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above information and the circuit shown in Figure 2, the
VIN rising (turn-on) threshold is:
VIN = 3µA •R1
( )
+1.225V
R1+R2
R2
and the VIN falling turn-off threshold is:
VIN =1.2
R1+R2
R2
when the voltage VOUT-IOUT reaches 58mV. The current
limit is:
IOUT(LIM) =
58mV
RSENSE
where RSENSE is the value of the sense resistor in ohms.
Most applications should use an output sense resistor as
shown in Figure 3, if practical. The internal buck-boost
power stage is current limited, but is nonetheless capable
of delivering large amounts of current in an overload
condition, especially when the output voltage is much
lower than the input and the power stage is operating as
a buck converter.
APPLICATIONS INFORMATION
RUN
LTM8056
VIN
R1
R2
8056 F02
Figure 2. This Simple Resistor Network Sets the Minimum
Operating Input Voltage Threshold with Hysteresis
IOUT
LTM8056
VOUT
RSENSE
8056 F03
LOAD
Figure 3. Set The LTM8056 Output Current Limit with an
External Sense Resistor
Minimum Input Voltage and SVIN
The minimum input voltage of the LTM8056 is 5V, but this
is only if VIN and SVIN are tied to the same voltage source.
If SVIN is powered from a power source at or above 5VDC,
VIN can be allowed to fall below 5V and the LTM8056 can
still operate properly. Some examples of this are provided
in the Typical Applications section.
Soft-Start
Soft-start reduces the input power sources’ surge currents
by gradually increasing the controller’s current. As indicated
in the Block Diagram, the LTM8056 has an internal soft-
start RC network. Depending upon the load and operating
conditions, the internal network may be sufficient for the
application. To increase the soft-start time, simply add a
capacitor from SS to GND.
Output Current Limit (IOUT)
The LTM8056 features an accurate average output current
limit set by an external sense resistor placed between VOUT
and IOUT as shown in Figure 3. VOUT and IOUT internally
connect to a differential amplifier that limits the current
When the voltage across the output sense resistor falls
to about 1/10th of full scale, the LL pin pulls low. If there
is no output sense resistor, and IOUT is tied to VOUT, LL
will be active low. Applying an output sense resistor and
tying the LL and MODE pins together can improve perfor-
mance—see Switching Mode in this section.
In high step-down voltage regulator applications, the
internal current limit can be quite high to allow proper
operation. This can potentially damage the LTM8056
in overload or short-circuit conditions. Apply an output
current sense resistor to set an appropriate current limit
to protect the LTM8056 against these fault conditions.
Output Current Limit Control (CTL)
Use the CTL input to reduce the output current limit from
the value set by the external sense resistor applied between
VOUT and IOUT. The typical control range is between 0V
and 1.2V. The CTL pin does not directly affect the input
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current limit. If this function is not used, leave CTL open.
Drive CTL to less than about 50mV to stop switching. The
CTL pin has an internal pull-up resistor to 2V.
Input Current Limit (IIN)
Some applications require that the LTM8056 draw no more
than some predetermined current from the power source.
Current limited power sources and power sharing are two
examples. The LTM8056 features an accurate input current
limit set by an external sense resistor placed between IIN
and VIN as shown in Figure 4. VIN and IIN internally connect
to a differential amplifier that limits the current when the
voltage IIN-VIN reaches 50mV. The current limit is:
IIN(LIM) =
50mV
RSENSE
where RSENSE is the value of the sense resistor in ohms.
If input current limiting is not required, simply tie IIN to VIN.
Synchronization
The LTM8056 switching frequency can be synchronized to
an external clock using the SYNC pin. Driving SYNC with
a 50% duty cycle waveform is a good choice, otherwise
maintain the duty cycle between about 10% and 90%. When
synchronizing, a valid resistor value (that is, a value that
results in a free-running frequency of 100kHz to 800kHz)
must be connected from RT to GND.
While an RT resistor is required for proper operation, the
value of this resistor is independent of the frequency of
the externally applied SYNC signal. Be aware, however,
that the LTM8056 will switch at the frequency prescribed
by the RT value if the SYNC signal terminates, so choose
an appropriate resistor value.
CLKOUT
The CLKOUT signal reflects the internal switching clock of
the LTM8056. It is phase shifted by approximately 180° with
respect to the leading edge of the internal clock. If CLKOUT
is connected to the SYNC input of another LTM8056, the
two devices will switch about 180° out of phase.
Input Precaution
In applications where the output voltage is deliberately
pulled up above the set regulation voltage or the FB pin is
abruptly driven to a new voltage, the LTM8056 may attempt
to regulate the voltage by removing energy from the load
for a short period of time after the output is pulled up.
Since the LTM8056 is a synchronous switching converter,
it delivers this energy to the input. If there is nothing on the
LTM8056 input to consume this energy, the input voltage
may rise. If the input voltage rises without intervention, it
may rise above the absolute maximum rating, damaging
the part. Carefully examine the input voltage behavior to
see if the application causes it to rise.
In many cases, the system load on the LTM8056 input
bus will be sufficient to absorb the energy delivered by the
μModule regulator. The power required by other devices
will consume more than enough to make up for what
APPLICATIONS INFORMATION
Figure 4. Set the LTM8056 Input Current Limit with an External
Sense Resistor
IIN
LTM8056
RSENSE
VIN
POWER
SOURCE
8056 F04
Input Current Monitor (IINMON)
The IINMON pin produces a voltage equal to approximately
20 times the voltage of IIN-VIN. Since the LTM8056 input
current limit engages when IIN-VIN = 50mV, IINMON will
be 1V at maximum input current.
Output Current Monitor (IOUTMON)
The IOUTMON pin produces a voltage proportional to the
voltage of VOUT-IOUT. Since the LTM8056 output current
limit engages when VOUT-IOUT = 58mV, IOUTMON will be
1.2V at maximum output current.
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the LTM8056 delivers. In cases where the LTM8056 is
the largest or only power converter, this may not be true
and some means may need to be devised to prevent the
LTM8056’s input from rising too high. Figure 5a shows a
passive crowbar circuit that will dissipate energy during
momentary input overvoltage conditions. The break-down
voltage of the Zener diode is chosen in conjunction with
the resistor R to set the circuit’s trip point. The trip point
is typically set well above the maximum VIN voltage under
normal operating conditions. This circuit does not have
a precision threshold, and is subject to both part-to-part
and temperature variations, so it is most suitable for ap-
plications where the maximum input voltage is much less
than the 60VIN absolute maximum. As stated earlier, this
type of circuit is best suited for momentary overvoltages.
Figure 5a is a crowbar circuit, which attempts to prevent
the input voltage from rising above some level by dumping
energy to GND through a power device. In some cases,
it is possible to simply turn off the LTM8056 when the
input voltage exceeds some threshold. An example of this
circuit is shown in Figure 5b. When the power source on
the output drives VIN above a predetermined threshold,
the comparator pulls down on the RUN pin and stops
switching in the LTM8056. When this happens, the input
capacitance needs to absorb the energy stored within the
LTM8056’s internal inductor, resulting in an additional
voltage rise. This voltage rise depends upon the input
capacitor size and how much current is flowing from the
LTM8056 output to input.
Switching Mode
The MODE pin allows the user to select either discontinuous
mode or forced continuous mode switching operation. In
forced continuous mode, the LTM8056 will not skip cycles,
even when the internal inductor current falls to zero or even
reverses direction. This has the advantage of operating at
the same fixed frequency for all load conditions, which can
be useful when designing to EMI or output noise speci-
fications. Forced continuous mode, however, uses more
current at light loads, and allows current to flow from the
load back into the input if the output is raised above the
regulation point. This reverse current can raise the input
voltage and be hazardous if the input is allowed to rise
uncontrollably. Please refer to Input Precautions in this
section for a discussion of this behavior.
Forced continuous operation may provide improved
output regulation when the LTM8056 transitions from
buck, buck-boost or boost operating modes, especially at
lighter loads. In such a case, it can be desirable to oper-
ate in forced continuous mode except when the internal
inductor current is about to reverse. If so, apply a current
sense resistor between VOUT and IOUT and tie the LL and
MODE pins together. The LL pin is low when the current
through the output sense resistor is about one-tenth the
full-scale maximum. When the output current falls to this
level, the LL pin will pull the MODE pin down, putting the
LTM8056 in discontinuous mode, preventing reverse cur-
rent from flowing from the output to the input. In the case
APPLICATIONS INFORMATION
VIN
ZENER
DIODE
R
Q
8056 F05a
LTM8056
LOAD
CURRENT
GND
VOUT
SOURCING
LOAD
VIN
RUN
8056 F05b
10µF
LTM8056
LOAD
CURRENT
GND
VOUT
SOURCING
LOAD
EXTERNAL
REFERENCE
VOLTAGE
+
–
Figure 5a. The MOSFET Q Dissipates Momentary Energy to
GND. The Zener Diode and Resistor Are Chosen to Ensure That
the MOSFET Turns On Above the Maximum VIN Voltage Under
Normal Operation
Figure 5b. This Comparator Circuit Turns Off the LTM8056 if
the Input Rises Above a Predetermined Threshold. When the
LTM8056 Turns Off, the Energy Stored in the Internal Inductor
Will Raise VIN a Small Amount Above the Threshold
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where MODE and LL are tied together, a small capacitor
(~0.1µF) from these pins to GND may improve the light
load transient response by delaying the transition from
the discontinuous to forced continuous switching modes.
MODE may be tied to GND for the purpose of blocking
reverse current if no output current sense resistor is used.
FB Resistor Divider and Load Regulation
The LTM8056 regulates its FB pin to 1.2V, using a resistor
divider to sense the output voltage. The location at which
the output voltage is sensed affects the load regulation.
If there is a current sense resistor between VOUT and
IOUT, and the output is sensed at VOUT, the voltage at the
load will drop by the value of the current sense resistor
multiplied by the output current. If the output voltage can
be sensed at IOUT, the load regulation may be improved.
PCB Layout
Most of the headaches associated with PCB layout have
been alleviated or even eliminated by the high level of
integration of the LTM8056. The LTM8056 is neverthe-
less a switching power supply, and care must be taken to
minimize EMI and ensure proper operation. Even with the
high level of integration, you may fail to achieve specified
operation with a haphazard or poor layout. See Figure 6
for a suggested layout. Ensure that the grounding and
heat sinking are acceptable.
A few rules to keep in mind are:
1. Place the RFB and RT resistors as close as possible to
their respective pins.
2. Place the CIN capacitor as close as possible to the VIN
and GND connection of the LTM8056.
3. Place the COUT capacitor as close as possible to the
VOUT and GND connection of the LTM8056.
4. Minimize the trace resistance between the optional
output current sense resistor, ROUT, and VOUT. Minimize
the loop area of the IOUT trace and the trace from VOUT
to ROUT.
5. Minimize the trace resistance between the optional input
current sense resistor (RIN) and VIN. Minimize the loop
area of the IIN trace and the trace from VIN to RIN.
6. Place the CIN and COUT capacitors such that their
ground current flow directly adjacent or underneath
the LTM8056.
7. Connect all of the GND connections to as large a copper
pour or plane area as possible on the top layer. Avoid
breaking the ground connection between the external
components and the LTM8056.
8. Use vias to connect the GND copper area to the board’s
internal ground planes. Liberally distribute these GND
vias to provide both a good ground connection and
thermal path to the internal planes of the printed circuit
board. Pay attention to the location and density of the
thermal vias in Figure 6. The LTM8056 can benefit from
the heat sinking afforded by vias that connect to internal
GND planes at these locations, due to their proximity
to internal power handling components. The optimum
number of thermal vias depends upon the printed
circuit board design. For example, a board might use
very small via holes. It should employ more thermal
vias than a board that uses larger holes.
Hot-Plugging Safely
The small size, robustness and low impedance of ceramic
capacitors make them an attractive option for the input
bypass capacitor of the LTM8056. However, these capaci-
tors can cause problems if the LTM8056 is plugged into a
live supply (see Linear Technology Application Note88 for
a complete discussion). The low loss ceramic capacitor
combined with stray inductance in series with the power
source forms an underdamped tank circuit, and the volt-
age at the VIN pin of the LTM8056 can ring to more than
twice the nominal input voltage, possibly exceeding the
LTM8056’s rating and damaging the part. If the input supply
APPLICATIONS INFORMATION
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is poorly controlled or the LTM8056 is hot-plugged into an
energized supply, the input network should be designed
to prevent this overshoot. This can be accomplished by
installing a small resistor in series with VIN, but the most
popular method of controlling input voltage overshoot is
to add an electrolytic bulk capacitor to the VIN net. This
capacitor’s relatively high equivalent series resistance
damps the circuit and eliminates the voltage overshoot.
The extra capacitor improves low frequency ripple filter-
ing and can slightly improve the efficiency of the circuit,
though it is likely to be the largest component in the circuit.
Thermal Considerations
The LTM8056 output current may need to be derated if
it is required to operate in a high ambient temperature or
deliver a large amount of continuous power. The amount
of current derating is dependent upon the input voltage,
output power and ambient temperature. The temperature
rise curves given in the Typical Performance Character-
istics section can be used as a guide. These curves were
generated by a LTM8056 mounted to a 58cm2 4-layer FR4
printed circuit board. Boards of other sizes and layer count
APPLICATIONS INFORMATION
Figure 6. Layout Showing Suggested External Components,
GND Plane and Thermal Vias
TO VOUT
GND
GND/THERMAL VIAS
GND
INPUT
RIN
INPUT
SENSE
8056 F06
COUT
VOUT
VIN
CIN
SVIN
LL RT
MODE SYNC
RUN
FB
IIN
ROUT
OUTPUT
SENSE
IOUT
IOUT
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APPLICATIONS INFORMATION
can exhibit different thermal behavior, so it is incumbent
upon the user to verify proper operation over the intended
system’s line, load and environmental operating conditions.
The thermal resistance numbers listed in the Pin Configura-
tion of the data sheet are based on modeling the µModule
package mounted on a test board specified per JESD 51-9
(Test Boards for Area Array Surface Mount Package Thermal
Measurements). The thermal coefficients provided on this
page are based on JESD 51-12 (Guidelines for Reporting
and Using Electronic Package Thermal Information).
For increased accuracy and fidelity to the actual application,
many designers use FEA to predict thermal performance.
To that end, the Pin Configuration of the data sheet typi-
cally gives four thermal coefficients:
θJA – Thermal resistance from junction to ambient.
θJCbottom – Thermal resistance from junction to the bottom
of the product case.
θJCtop – Thermal resistance from junction to top of the
product case.
θJB – Thermal resistance from junction to the printed
circuit board.
While the meaning of each of these coefficients may seem
to be intuitive, JEDEC has defined each to avoid confusion
and inconsistency. These definitions are given in JESD
51-12, and are quoted or paraphrased below:
θJA is the natural convection junction-to-ambient air
thermal resistance measured in a one cubic foot sealed
enclosure. This environment is sometimes referred to as
“still air” although natural convection causes the air to
move. This value is determined with the part mounted to
a JESD 51-9 defined test board, which does not reflect an
actual application or viable operating condition.
θJCbottom is the thermal resistance between the junction
and bottom of the package with all of the component power
dissipation flowing through the bottom of the package. In
the typical µModule converter, the bulk of the heat flows
out the bottom of the package, but there is always heat
flow out into the ambient environment. As a result, this
thermal resistance value may be useful for comparing
packages but the test conditions don’t generally match
the user’s application.
θJCtop is determined with nearly all of the component power
dissipation flowing through the top of the package. As the
electrical connections of the typical µModule converter are
on the bottom of the package, it is rare for an application
to operate such that most of the heat flows from the junc-
tion to the top of the part. As in the case of θJCbottom, this
value may be useful for comparing packages but the test
conditions don’t generally match the user’s application.
θJB is the junction-to-board thermal resistance where
almost all of the heat flows through the bottom of the
µModule converter and into the board, and is really the
sum of the θJCbottom and the thermal resistance of the
bottom of the part through the solder joints and through a
portion of the board. The board temperature is measured
a specified distance from the package, using a 2-sided,
2-layer board. This board is described in JESD 51-9.
Given these definitions, it should now be apparent that none
of these thermal coefficients reflects an actual physical
operating condition of a µModule converter. Thus, none
of them can be individually used to accurately predict the
thermal performance of the product. Likewise, it would
be inappropriate to attempt to use any one coefficient to
correlate to the junction temperature versus load graphs
given in the product’s data sheet. The only appropriate way
to use the coefficients is when running a detailed thermal
analysis, such as FEA, which considers all of the thermal
resistances simultaneously.
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A graphical representation of these thermal resistances
is given in Figure 7.
The blue resistances are contained within the µModule
converter, and the green are outside.
The die temperature of the LTM8056 must be lower than
the maximum rating of 125°C, so care should be taken in
the layout of the circuit to ensure good heat sinking of the
LTM8056. The bulk of the heat flow out of the LTM8056
is through the bottom of the μModule converter and the
BGA pads into the printed circuit board. Consequently a
poor printed circuit board design can cause excessive
heating, resulting in impaired performance or reliability.
Please refer to the PCB Layout section for printed circuit
board design suggestions.
8056 F07
µMODULE CONVERTER
JUNCTION-TO-CASE (TOP)
RESISTANCE
JUNCTION-TO-BOARD RESISTANCE
JUNCTION-TO-AMBIENT RESISTANCE (JESD 51-9 DEFINED BOARD)
CASE (TOP)-TO-AMBIENT
RESISTANCE
BOARD-TO-AMBIENT
RESISTANCE
JUNCTION-TO-CASE
(BOTTOM) RESISTANCE
JUNCTION AMBIENT
CASE (BOTTOM)-TO-BOARD
RESISTANCE
Figure 7
APPLICATIONS INFORMATION
LTM8056
21
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For more information www.linear.com/LTM8056
TYPICAL APPLICATIONS
18VOUT Fan Power from 3VIN to 58VIN with Analog
Current Control and 2A Input Current Limiting
Maximum Output Current
vs CTL Voltage 12VIN
Output Voltage vs Output Current
24VOUT from 9VIN to 58VIN with 1.1A Accurate Current Limit
VIN SVIN
IIN
GNDLLMODE
FAN CONTROL
LTM8056
IOUT
0.05Ω
VOUT
CLKOUT
IINMON
IOUTMON
FB
RUN
COMP
SS
SYNC
CTL
RT
0.022Ω
6.98k
100k
8056 TA02a
22µF
25V
47µF
25V
VOUT
18V MAX
FAN
2.2µF
100V
×3
1µF
100V
VIN
3V TO 58V
31.6k
fSW = 650kHz
DAC
+
VIN
SVIN
IIN
GNDLLMODE
LTM8056
IOUT
0.05Ω
VOUT
CLKOUT
IINMON
IOUTMON
FB
RUN
CTL
SS
SYNC
COMP
RT
5.23k
8056 TA03a
22µF
25V
33µF
35V
VOUT
24V
2.2µF
100V
×3
VIN
9V TO 58V
43.2k
fSW = 525kHz
100k
+
CTL VOLTAGE (V)
0
OUTPUT CURRENT (A)
1.2
0.8
0.6
1.0
0.4
0.2
0
8056 TA02b
1.20.6 0.80.2 0.4 1
OUTPUT CURRENT (A)
0
OUTPUT VOLTAGE (V)
25
15
20
10
5
0
8056 TA03b
1.510.5
12VIN
24VIN
36VIN
48VIN
LTM8056
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For more information www.linear.com/LTM8056
18VOUT from 18VIN to 58VIN with 2.5A Accurate Current Limit
and Output Current Monitor
TYPICAL APPLICATIONS
Tw o LTM8056s Paralleled to Get More Output Current. The Tw o µModules Are
Synchronized and Switching 180° Out Of Phase
VIN
SVIN
IIN
GNDLLMODE
LTM8056
IOUT
0.022Ω
VOUT
CLKOUT
IINMON
IOUTMON
FB
RUN
CTL
SS
SYNC
COMP
RT
6.98k 8056 TA04a
22µF
25V
47µF
25V
VOUT
18V
OUTPUT
CURRENT
MONITOR
2.2µF
100V
×3
VIN
18V TO 58V
31.6k
fSW = 650kHz
100k +
Output Voltage vs Output Current
Output Current per Channel vs
Total Output Current
OUTPUT CURRENT (A)
NOTE: LINES ARE SUPERIMPOSED
0
OUTPUT VOLTAGE (V)
20
14
18
16
12
10
8
4
2
6
0
8056 TA04b
32 2.510.5 1.5
24VIN
36VIN
48VIN
VIN
SVIN
IIN
GNDLLMODE
LTM8056
IOUT
0.015Ω
VOUT
IINMON
IOUTMON
FB
RUN
CTL
SS
SYNC
COMP
RT
CLKOUT
VOUT
18V
2.2µF
100V
×4 1µF
VIN
7V TO 58V
30.9k
VIN
SVIN
IIN
GND
LTM8056
IOUT
0.015Ω
VOUT
CTL
CLKOUT
IINMON
IOUTMON
FB
RUN
COMP
SS
SYNC
RT
6.98k
LT6015
100k
6.34k
8056 TA05a
2.2µF
100V
×4
1µF
30.9k
fSW = 680kHz
LLMODE
51Ω
100k
22µF
25V 47µF
25V
22µF
25V
47µF
25V
+
+
TOTAL OUTPUT CURRENT (A)
0
CHANNEL CURRENT (A)
4
2
3
1
0
8056 TA05b
842 6
MASTER
SLAVE
NOTE: LINES ARE SUPERIMPOSED
LTM8056
23
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For more information www.linear.com/LTM8056
TYPICAL APPLICATIONS
Tw o LTM8056s Powered from Different Input Sources to Run a Single Load. Each LTM8056 Draws No More Than 1.1A from Its
Respective Power Sources, and Are Synchronized 180° Out Of Phase with Each Other
VIN
SVIN
IIN
GNDLLMODE
LTM8056
IOUT
VOUT
IINMON
IOUTMON
FB
RUN
CTL
SS
SYNC
COMP
RT
CLKOUT
22µF
25V
47µF
35V
VOUT
18V
2.2µF
100V
×3
SUPPLY 1
6V TO 58VIN
SUPPLY 2
6V TO 58VIN
31.6k
VIN
0.045Ω
0.045Ω
SVIN
IIN
GND
LTM8056
IOUT
VOUT
CLKOUT
IINMON
IOUTMON
FB
RUN
CTL
SS
SYNC
COMP
RT
6.98k
8056 TA06a
22µF
25V
2.2µF
100V
×3
31.6k
fSW = 650kHz
LLMODE
100k
+
OUTPUT CURRENT (A)
0
CHANNEL INPUT CURRENT (A)
1.2
0.6
0.8
1.0
0.4
0.2
0
8056 TA06b
731 2 654
CHANNEL 1
CHANNEL 2
Input Current per Channel vs
Total Output Current
LTM8056
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For more information www.linear.com/LTM8056
PACKAGE DESCRIPTION
Table 4. LTM8056 Pin Assignment (Arranged by Pin Number)
PIN ID FUNCTION PIN ID FUNCTION PIN ID FUNCTION PIN ID FUNCTION PIN ID FUNCTION PIN ID FUNCTION
A1 VOUT B1 VOUT C1 VOUT D1 IOUT E1 GND F1 LL
A2 VOUT B2 VOUT C2 VOUT D2 GND E2 GND F2 GND
A3 VOUT B3 VOUT C3 VOUT D3 GND E3 GND F3 GND
A4 VOUT B4 VOUT C4 VOUT D4 GND E4 GND F4 GND
A5 VOUT B5 VOUT C5 VOUT D5 GND E5 GND F5 GND
A6 VOUT B6 VOUT C6 VOUT D6 GND E6 GND F6 GND
A7 GND B7 GND C7 GND D7 GND E7 GND F7 GND
A8 GND B8 GND C8 GND D8 GND E8 GND F8 GND
A9 GND B9 GND C9 GND D9 GND E9 GND F9 GND
A10 GND B10 GND C10 GND D10 GND E10 GND F10 SVIN
A11 GND B11 GND C11 GND D11 GND E11 GND F11 SVIN
PIN ID FUNCTION PIN ID FUNCTION PIN ID FUNCTION PIN ID FUNCTION PIN ID FUNCTION
G1 CLKOUT H1 RT J1 FB K1 SS L1 GND
G2 MODE H2 SYNC J2 COMP K2 CTL L2 IOUTMON
G3 GND H3 GND J3 GND K3 GND L3 IINMON
G4 GND H4 GND J4 GND K4 GND L4 RUN
G5 GND H5 GND J5 GND K5 GND L5 GND
G6 GND H6 GND J6 GND K6 GND L6 GND
G7 GND H7 GND J7 GND K7 GND L7 GND
G8 GND H8 GND J8 GND K8 GND L8 GND
G9 GND H9 GND J9 GND K9 GND L9 IIN
G10 VIN H10 VIN J10 VIN K10 VIN L10 VIN
G11 VIN H11 VIN J11 VIN K11 VIN L11 VIN
LTM8056
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For more information www.linear.com/LTM8056
PACKAGE DESCRIPTION
PACKAGE TOP VIEW
4
PIN “A1”
CORNER
YX
aaa Z
aaa Z
DETAIL A
PACKAGE BOTTOM VIEW
3
SEE NOTES
L
K
J
H
G
F
E
D
C
B
A
123891011 4567
PIN 1
BGA Package
121-Lead (15.00mm × 15.00mm × 4.92mm)
(Reference LTC DWG# 05-08-1891 Rev A)
NOTES:
1. DIMENSIONING AND TOLERANCING PER ASME Y14.5M-1994
2. ALL DIMENSIONS ARE IN MILLIMETERS
BALL DESIGNATION PER JESD MS-028 AND JEP95
5. PRIMARY DATUM -Z- IS SEATING PLANE
6. SOLDER BALL COMPOSITION CAN BE 96.5% Sn/3.0% Ag/0.5% Cu
OR Sn Pb EUTECTIC
4
3
DETAILS OF PIN #1 IDENTIFIER ARE OPTIONAL,
BUT MUST BE LOCATED WITHIN THE ZONE INDICATED.
THE PIN #1 IDENTIFIER MAY BE EITHER A MOLD OR
MARKED FEATURE
DETAIL A
Øb (121 PLACES)
DETAIL B
SUBSTRATE
A
A1
b1
ccc Z
DETAIL B
PACKAGE SIDE VIEW
MOLD
CAP
Z
MX YZddd
MZeee
SYMBOL
A
A1
A2
b
b1
D
E
e
F
G
H1
H2
aaa
bbb
ccc
ddd
eee
MIN
4.72
0.50
4.22
0.71
0.610
0.27
3.95
NOM
4.92
0.60
4.32
0.78
0.635
15.00
15.00
1.27
12.70
12.70
0.32
4.00
MAX
5.12
0.70
4.42
0.85
0.660
0.37
4.05
0.15
0.10
0.20
0.30
0.15
NOTES
DIMENSIONS
TOTAL NUMBER OF BALLS: 121
A2
D
E
e
b
F
G
SUGGESTED PCB LAYOUT
TOP VIEW
0.000
3.810
5.080
3.810
6.350
5.080
6.350
2.540
1.270
2.540
1.270
6.350
5.080
1.270
6.350
5.080
3.810
2.540
1.270
0.3175
0.3175
3.810
2.540
0.000
// bbb Z
Z
H2
H1
0.635 ±0.025 Ø 121x
LTMXXXXXX
µModule
BGA 121 1112 REV A
TRAY PIN 1
BEVEL PACKAGE IN TRAY LOADING ORIENTATION
COMPONENT
PIN “A1”
7 PACKAGE ROW AND COLUMN LABELING MAY VARY
AMONG µModule PRODUCTS. REVIEW EACH PACKAGE
LAYOUT CAREFULLY
!
7
SEE NOTES
Please refer to http://www.linear.com/product/LTM8056#packaging for the most recent package drawings.
LTM8056
27
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For more information www.linear.com/LTM8056
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 representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
REVISION HISTORY
REV DATE DESCRIPTION PAGE NUMBER
A 11/16 Added text to IOUTMON (Pin L2)
Added Buck-Boost Selection Table
8
1
LTM8056
28
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For more information www.linear.com/LTM8056
LINEAR TECHNOLOGY CORPORATION 2015
LT 1116 REV A • PRINTED IN USA
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LTM8056
DESIGN RESOURCES
SUBJECT DESCRIPTION
µModule Design and Manufacturing Resources Design:
• Selector Guides
• Demo Boards and Gerber Files
• Free Simulation Tools
Manufacturing:
• Quick Start Guide/Demo Manual
• PCB Design, Assembly and Manufacturing Guidelines
• Package and Board Level Reliability
µModule Regulator Products Search 1. Sort table of products by parameters and download the result as a spread sheet.
2. Search using the Quick Power Search parametric table.
TechClip Videos Quick videos detailing how to bench test electrical and thermal performance of µModule products.
Digital Power System Management Linear Technology’s family of digital power supply management ICs are highly integrated solutions that
offer essential functions, including power supply monitoring, supervision, margining and sequencing,
and feature EEPROM for storing user configurations and fault logging.
PART NUMBER DESCRIPTION COMMENTS
LTM8055 Higher Power, Pin Compatible 8.5A, 5V ≤ VIN ≤ 36V
LTM4605 Higher Power Buck-Boost (Up to 60W) External Inductor, Synchronous Switching Buck-Boost; Up to 36VIN, 0.8V ≤ VOUT
≤ 16V
LTM4607 Higher Power Buck-Boost (Up to 60W) External Inductor, Synchronous Switching Buck-Boost; Up to 36VIN, 0.8V ≤ VOUT
≤ 24V
LTM4609 Higher Power Buck-Boost (Up to 60W) External Inductor, Synchronous Switching Buck-Boost; Up to 36VIN, 0.8V ≤ VOUT
≤ 34V
LTM8045 Smaller, Lower Power SEPIC and Inverting; 700mA, 6.25mm × 11.25mm × 4.92mm BGA
LTM8046 Isolated, Lower Power Flyback Topology, 550mA (5VOUT, 24VIN), UL60950, 2kVAC
RELATED PARTS
TYPICAL APPLICATION
14.4V, 3A Lead-Acid Battery Charger Input Current Limited to 2A Maximum Input and Output Current
vs Input Voltage
VIN SVIN
IIN
GNDLLMODE
LTM8056
IOUT
0.018Ω
VOUT
CLKOUT
IINMON
IOUTMON
FB
RUN
CTL
SS
SYNC
COMP
RT
0.022Ω
9.09k
100k
8056 TA07a
22µF
25V
47µF
25V
VOUT
14.4V
1µF
100V
2.2µF
100V
×3
VIN
3V TO 58V
31.6k
fSW = 650kHz
+
INPUT VOLTAGE (V)
OUTPUT
INPUT
0
INPUT CURRENT (A)
OUTPUT CURRENT (A)
3.5
2.0
2.5
3.0
1.5
1.0
0.5
0
3.5
2.0
2.5
3.0
1.5
1.0
0.5
0
8056 TA07b
6020 40
