LINER LTM8031 Ultralow noise emc 36v, 1a dc/dc î¼module regulator Datasheet

LTM8031
Ultralow Noise EMC 36V, 1A
DC/DC µModule Regulator
FEATURES
DESCRIPTION
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The LTM®8031 is an electromagnetic compatible (EMC)
36V, 1A DC/DC μModule® buck converter designed to
meet the radiated emissions requirements of EN55022.
Conducted emission requirements can be met by adding
standard filter components. Included in the package are the
switching controller, power switches, inductor, filters and
all support components. Operating over an input voltage
range of 3.6V to 36V, the LTM8031 supports an output
voltage range of 0.8V to 10V, and a switching frequency
range of 200kHz to 2.4MHz, each set by a single resistor.
Only the bulk input and output filter capacitors are needed
to finish the design. The low profile package (2.82mm)
enables utilization of unused space on the bottom of PC
boards for high density point of load regulation.
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Complete Step-Down Switch Mode Power Supply
Wide Input Voltage Range: 3.6V to 36V
1A Output Current
0.8V to 10V Output Voltage
Switching Frequency from 200kHz to 2.4MHz
EN55022 Class B Compliant
Current Mode Control
(e4) RoHS Compliant Package with Gold Pad Finish
Programmable Soft-Start
Low Profile (9mm × 15mm × 2.82mm)
Surface Mount LGA Package
APPLICATIONS
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Automotive Battery Regulation
Power for Portable Products
Distributed Supply Regulation
Industrial Supplies
Wall Transformer Regulation
The LTM8031 is packaged in a thermally enhanced, compact
(9mm × 15mm) and low profile (2.82mm) overmolded land
grid array (LGA) package suitable for automated assembly
by standard surface mount equipment. The LTM8031 is
RoHS compliant.
L, LT, LTC, LTM, μModule, Linear Technology and the Linear logo are registered trademarks of
Linear Technology Corporation. All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
Ultralow Noise 5V/1A DC/DC μModule Regulator
OUT
VIN
10μF
FIN
LTM8031
RUN/SS
AUX
BIAS
1μF
SHARE
PGOOD
RT SYNC GND ADJ
44.2k
47.5k
8031 TA01a
VOUT
5V
1A
80
EMISSIONS LEVEL (dBμV/m)
VIN*
7VDC TO 36VDC
LTM8031 EMI Performance
VIN = 36V
70
60
50
EN55022
CLASS B
LIMIT
40
30
20
10
0
*RUNNING VOLTAGE RANGE.
SEE APPLICATIONS FOR START-UP DETAILS
–10
0 100 200 300 400 500 600 700 800 900 1000
FREQUENCY (MHz)
8031 TA01b
8031fa
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LTM8031
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
VIN, FIN, RUN/SS Voltage..........................................40V
ADJ, RT, SHARE Voltage .............................................5V
VOUT, AUX .................................................................10V
Current from AUX ................................................100mA
PGOOD, SYNC ..........................................................30V
BIAS ..........................................................................25V
VIN + BIAS .................................................................56V
Maximum Junction Temperature (Note 2)............. 125°C
Solder Temperature (Note 3)................................. 245°C
1
2
TOP VIEW
3
4
5
VOUT
6
GND
7
A
BANK 1
B
C
D
E
BANK 2
F
G
RT
H
SHARE
BIAS
J
ADJ
AUX
PGOOD
K
BANK 3
L
VIN
FIN RUN/SS SYNC
LGA PACKAGE
71-LEAD (9mm s 15mm s 2.82mm)
TJMAX = 125°C, θJA = 20.7°C/W, θJC(BOTTOM) = 8.4°C/W,
θJC(TOP) = 25.6°C/W, θJBOARD = 13.8°C/W
θ VALUES DETERMINED PER JESD 51-9
WEIGHT = 1.2g
ORDER INFORMATION
LEAD FREE FINISH
TRAY
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTM8031EV#PBF
LTM8031EV#PBF
LTM8031V
71-Lead (9mm × 15mm × 2.82mm) LGA
–40°C to 125°C
LTM8031IV#PBF
LTM8031IV#PBF
LTM8031V
71-Lead (9mm × 15mm × 2.82mm) LGA
–40°C to 125°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/
8031fa
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LTM8031
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 10V, VRUN/SS = 10V, VBIAS = 3V, unless otherwise specified.
SYMBOL
PARAMETER
VIN
Input DC Voltage
VOUT
Output DC Voltage
0.2A < IOUT ≤ 1A, RADJ Open
0.2A < IOUT ≤ 1A, RADJ = 21.6k
IOUT
Continuous Output DC Current
VIN = 24V
IQ(VIN)
VIN Quiescent Current
VRUN/SS = 0.2V
VBIAS = 3V, Not Switching
VBIAS = 0V, Not Switching
l
VRUN/SS = 0.2V
VBIAS = 3V, Not Switching
VBIAS = 0V, Not Switching
l
IQ(BIAS)
ΔVOUT
VOUT
BIAS Quiescent Current
CONDITIONS
MIN
l
TYP
3.6
MAX
UNITS
36
V
0.8
10
V
V
1
A
0.6
25
88
60
120
μA
μA
μA
0.03
60
1
120
5
μA
μA
μA
Line Regulation
10V ≤ VIN ≤ 36V, IOUT = 1A, VOUT = 3.3V
0.1
Load Regulation
VIN = 24V, 0.2A ≤ IOUT ≤ 1A, VOUT = 3.3V
0.3
%
6
mV
VOUT(AC_RMS) Output Ripple (RMS)
fSW
Switching Frequency
VADJ
Voltage at ADJ Pin
VBIAS(MIN)
Minimum BIAS Voltage for Proper Operation
VIN = 24V, IOUT = 1A, VOUT = 3.3V
RT = 113k
%
325
l
765
kHz
790
815
mV
1.9
2.8
V
10
μA
IADJ
Current Out of ADJ Pin
VRUN/SS = 0V, VADJ = 0V, VOUT = 1V
4
IRUN/SS
RUN/SS Pin Current
VRUN/SS = 2.5V
5
VIH(RUN/SS)
RUN/SS Input High Voltage
VIL(RUN/SS)
RUN/SS Input Low Voltage
VPG(TH)
ADJ Voltage Threshold for PGOOD to Switch
μA
2.5
V
0.2
730
IPGO
PGOOD Leakage
VPG = 30V
IPGSINK
PGOOD Sink Current
VPG = 0.4V
VSYNCIL
SYNC Input Low Threshold
fSYNC = 550kHz
VSYNCIH
SYNC Input High Threshold
fSYNC = 550kHz
ISYNC(BIAS)
SYNC Pin Bias Current
VSYNC = 0V, VBIAS = 0V
0.1
μA
VIN(RIPPLE)
550kHz Narrowband Conducted Emission
1MHz Narrowband Conducted Emission
3MHz Narrowband Conducted Emission
VIN = 24V, VOUT = 3.3V, IOUT = 1A, fSW = 550kHz,
5μH LISN
83
63
51
dBμV
dBμV
dBμV
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 LTM8031E is guaranteed to meet performance specifications
from 0°C to 125°C internal. Specifications over the –40°C to 125°C
internal temperature range are assured by design, characterization and
0.1
V
mV
200
1
800
μA
μA
0.5
V
0.7
V
correlation with statistical process controls. The LTM8031I is guaranteed
to meet specifications over the full –40°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: See Linear Technology Application Note 100.
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LTM8031
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted.
3.3VOUT Efficiency
5VOUT Efficiency
90
90
80
80
80
70
60
5VIN
12VIN
24VIN
36VIN
EFFICIENCY (%)
90
EFFICIENCY (%)
100
EFFICIENCY (%)
100
50
70
60
12VIN
24VIN
36VIN
50
40
200
200
300
200
350
300
250
200
150
100
100
200
400
800
600
OUTPUT CURRENT (mA)
0
1000
0
200
600
800
400
OUTPUT CURRENT (mA)
8031 G04
400
300
200
0
1000
0
200
400
800
600
OUTPUT CURRENT (mA)
1000
8031 G06
Minimum VIN vs Output Current
3.3V VOUT
Minimum VIN vs Output Current
5V VOUT
6.1
5.0
7.6
4.8
7.1
5.6
RUN/SS = VIN OR TOGGLED
6.6
RUN/SS = VIN
VIN (V)
4.4
4.2
5.1
4.6
4.0
RUNNING OR RUN/SS TOGGLED
4.6
RUNNING
4.1
RUNNING
5.6
5.1
RUN/SS TOGGLED
3.8
RUN/SS = VIN
6.1
VIN (V)
4.6
VIN (V)
500
8031 G05
Minimum VIN vs Output Current
2.5V VOUT
3.6
3.4
600
100
50
0
12VIN
24VIN
36VIN
700
INPUT CURRENT (mA)
INPUT CURRENT (mA)
400
800
12VIN
24VIN
36VIN
400
500
0
Input Current vs Output Current,
8VOUT
500
450
1000
400
600
800
OUTPUT CURRENT (mA)
8031 G03
Input Current vs Output Current,
5VOUT
800
600
200
8031 G02
Input Current vs Output Current,
3.3VOUT
5VIN
12VIN
24VIN
36VIN
12VIN
24VIN
36VIN
0
1000
400
600
800
OUTPUT CURRENT (mA)
8031 G01
700
60
40
0
1000
400
600
800
OUTPUT CURRENT (mA)
70
50
40
0
INPUT CURRENT (mA)
8VOUT Efficiency
100
4.1
0
200
400
800
600
OUTPUT CURRENT (mA)
1000
8031 G07
3.6
0
200
600
800
400
OUTPUT CURRENT (mA)
1000
8031 G08
3.6
0
200
400
800
600
OUTPUT CURRENT (mA)
1000
8031 G09
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LTM8031
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted.
Minimum VIN vs Output Current
8V VOUT
Minimum Input Running Voltage
vs Output Voltage, IOUT = 1A
12
11
RUN/SS = VIN
14
30
VIN (V)
10
8
8
7
6
6
4
5
2
200
0
800
600
OUTPUT CURRENT (mA)
0
BIAS CURRENT (mA)
RUNNING OR RUN/SS TOGGLED
9
VIN (V)
35
12
10
4
400
1000
0
2
4
8
6
VOUT (V)
1.2
2.60
2.55
2.50
2.45
12
16
20
28
32
0.8
0.6
0.4
36
15
10
10
20
30
0
40
0
200
Temperature Rise vs
Load Current, VOUT = 10V
30
36VIN
24VIN
12VIN
5
20
15
10
5
0
1000
8031 G16
36VIN
24VIN
25
TEMPERATURE RISE (°C)
TEMPERATURE RISE (°C)
25
10
1000
8031 G15
30
15
400
600
800
OUTPUT CURRENT (mA)
8031 G14
Temperature Rise vs
Load Current, VOUT = 8V
20
400
600
800
OUTPUT CURRENT (mA)
20
VIN (V)
36VIN
24VIN
12VIN
200
36VIN
24VIN
12VIN
5VIN
5
0
30
1000
Temperature Rise vs
Load Current, VOUT = 3.3V
1.0
Temperature Rise vs
Load Current, VOUT = 5V
1
400
600
800
OUTPUT CURRENT (mA)
8031 G12
25
8031 G13
25
200
30
VIN (V)
TEMPERATURE RISE (°C)
0
0
24
10
0
0.2
2.40
8
15
10
TEMPERATURE RISE (°C)
2.70
INPUT CURRENT (A)
OUTPUT CURRENT (A)
1.4
4
20
Input Current vs Input Voltage
(Output Shorted)
2.75
0
25
8031 G11
Output Current vs Input Voltage
(Output Shorted)
2.65
8VOUT
5VOUT
3.3VOUT
5
8031 G10
2.35
Bias Current vs Output Current
16
20
15
10
5
0
0
1
200
400
600
800
OUTPUT CURRENT (mA)
1000
8031 G17
1
200
400
600
800
OUTPUT CURRENT (mA)
1000
8031 G18
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LTM8031
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted.
Radiated Emissions
EMISSIONS LEVEL (dBμV/m)
80
Radiated Emissions
90
VIN = 36V
VOUT = 10V AT 1A
80
70
60
50
EN55022
CLASS B
LIMIT
40
30
20
10
EMISSIONS LEVEL (dBμV/m)
90
70
60
50
30
20
10
0
–10
–10
8031 G19
EN55022
CLASS B
LIMIT
40
0
0 100 200 300 400 500 600 700 800 900 1000
FREQUENCY (MHz)
VIN = 36V
VOUT = 2.5V AT 1A
0 100 200 300 400 500 600 700 800 900 1000
FREQUENCY (MHz)
8031 G20
PIN FUNCTIONS
VIN (Bank 3): The VIN pin supplies current to the LTM8031’s
internal regulator and to the internal power switch. This
pin must be locally bypassed with an external, low ESR
capacitor of at least 1μF .
FIN (K3, L3): Filtered Input. This is the node after the input
EMI filter. Use this only if there is a need to modify the
behavior of the integrated EMI filter or if VIN rises or falls
rapidly; otherwise, leave these pins unconnected. See the
Applications Information section for more details.
GND (Bank 2): Tie these GND pins to a local ground plane
below the LTM8031 and the circuit components. Return
the feedback divider (RADJ) to this net.
VOUT (Bank 1): Power Output Pins. Apply the output filter
capacitor and the output load between these pins and
GND pins.
AUX (Pin H5): Low Current Voltage Source for BIAS. In
many designs, the BIAS pin is simply connected to VOUT .
The AUX pin is internally connected to VOUT and is placed
adjacent to the BIAS pin to ease printed circuit board routing. Although this pin is internally connected to VOUT , do
not connect this pin to the load. If this pin is not tied to
BIAS, leave it floating.
BIAS (Pin H4): The BIAS pin connects to the internal power
bus. Connect to a power source greater than 2.8V. If the
output is greater than 2.8V, connect this pin to AUX. If the
output voltage is less, connect this to a voltage source
between 2.8V and 25V. Also, make sure that BIAS + VIN
is less than 56V.
RUN/SS (Pin L5): Pull RUN/SS pin to less than 0.2V to
shut down the LTM8031. Tie to 2.5V or more for normal
operation. If the shutdown feature is not used, tie this pin
to the VIN pin. RUN/SS also provides a soft-start function;
see the Applications Information section.
RT (Pin G7): The RT pin is used to program the switching
frequency of the LTM8031 by connecting a resistor from
this pin to ground. 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.
SHARE (Pin H7): Tie this to the SHARE pin of another
LTM8031 when paralleling the outputs.
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LTM8031
PIN FUNCTIONS
SYNC (Pin L6): This is the external clock synchronization
input. Ground this pin for low ripple Burst Mode® operation
at low output loads. Tie to a stable voltage source greater
than 0.7V to disable Burst Mode operation. Do not leave
this pin floating. Tie to a clock source for synchronization. Clock edges should have rise and fall times faster
than 1μs. See Synchronization section in Applications
Information.
PGOOD (Pin K7): The PGOOD pin is the open-collector
output of an internal comparator. PGOOD remains low until
the ADJ pin is within 10% of the final regulation voltage.
The PGOOD output is valid when VIN is above 3.6V and
RUN/SS is high. If this function is not used, leave this
pin floating.
ADJ (Pin J7): The LTM8031 regulates its ADJ pin to 0.79V.
Connect the adjust resistor from this pin to ground. The
value of RADJ is given by the equation:
R ADJ =
196.71
VOUT – 0.79
where RADJ is in kΩ.
Burst Mode is a registered trademark of Linear Technology Corporation.
BLOCK DIAGRAM
FIN
VIN
EMI FILTER
4.7μH
VOUT
AUX
22pF
249k
GND
10μF
GND
BIAS
SHARE
CURRENT
MODE
CONTROLLER
RUN/SS
SYNC
RT
PGOOD
ADJ
8031 BD
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LTM8031
OPERATION
The LTM8031 is a standalone nonisolated step-down
switching DC/DC power supply. It can deliver up to 1A of
DC output current with only bulk external input and output
capacitors. This module provides a precisely regulated
output voltage programmable via one external resistor
from 0.8VDC to 10VDC. The input voltage range is 3.6V
to 36V. Given that the LTM8031 is a step-down converter,
make sure that the input voltage is high enough to support
the desired output voltage and load current. A simplified
Block Diagram is given on the previous page.
The LTM8031 is designed with an input EMI filter and other
features to make its radiated emissions compliant with
several EMC specifications including EN55022 class B.
Compliance with conducted emissions requirements may
be obtained by adding a standard input filter.
The LTM8031 contains a current mode controller, power
switching element, power inductor, power Schottky diode
and a modest amount of input and output capacitance. The
LTM8031 is a fixed frequency PWM regulator. The switching frequency is set by simply connecting the appropriate
resistor value from the RT pin to GND.
An internal regulator provides power to the control circuitry.
The bias regulator can draw power from the VIN pin, but if
the BIAS pin is connected to an external voltage higher than
2.8V, bias power will be drawn from the external source
(typically the regulated output voltage). This improves
efficiency. The RUN/SS pin is used to place the LTM8031
in shutdown, disconnecting the output and reducing the
input current to less than 1μA.
To further optimize efficiency, the LTM8031 automatically
switches to Burst Mode operation in light load situations.
Between bursts, all circuitry associated with controlling the
output switch is shut down reducing the input supply current to 50μA in a typical application. The oscillator reduces
the LTM8031’s operating frequency when the voltage at the
ADJ pin is low. This frequency foldback helps to control
the output current during start-up and overload.
The LTM8031 contains a power good comparator which
trips when the ADJ pin is at 90% of its regulated value.
The PGOOD output is an open-collector transistor that is
off when the output is in regulation, allowing an external
resistor to pull the PGOOD pin high. Power good is valid
when the LTM8031 is enabled and VIN is above 3.6V.
APPLICATIONS INFORMATION
For most applications, the design process is straight
forward, 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, RADJ and RT
values.
3. Connect BIAS as indicated.
As the integrated input EMI filter may ring in response to an
application of a step input voltage, a bulk capacitance, series
resistance or some clamping mechanism may be required.
See the Hot-Plugging Safely section for details.
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.
Capacitor Selection Considerations
The CIN and COUT capacitor values in Table 1 are the
minimum recommended values for the associated operating 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 applied
voltage and give dependable service. Other types, including Y5V and Z5U have very large temperature and voltage
coefficients of capacitance. In an application circuit they
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LTM8031
APPLICATIONS INFORMATION
Table 1. Recommended Component Values and Configuration (See Typical Performance Characteristics for Load Conditions)
VIN
VOUT
CIN
COUT
RADJ
BIAS
fOPTIMAL
RT(OPTIMAL)
fMAX
RT(MIN)
3.6V to 36V
0.82V
1μF 0805 50V
2 × 100μF 1206 6.3V
5.11M
≥2.8V, <25V
250kHz
150k
250kHz
150k
3.6V to 36V
1.20V
1μF 0805 50V
100μF//47μF 1206 6.3V
475k
≥2.8V, <25V
300kHz
124k
325kHz
113k
3.6V to 36V
1.80V
1μF 0805 50V
100μF 1206
191k
≥2.8V, <25V
420kHz
84.5k
450kHz
78.7k
3.6V to 36V
2.00V
1μF 0805 50V
100μF 1206
162k
≥2.8V, <25V
450kHz
78.7k
475kHz
73.2k
3.6V to 36V
2.50V
1μF 0805 50V
47μF 0805 6.3V
115k
≥2.8V, <25V
550kHz
61.9k
575kHz
59.0k
4.75V to 36V
3.30V
1μF 0805 50V
22μF 1206 6.3V
78.7k
AUX
675kHz
48.7k
725kHz
44.2k
6.8V to 36V
5.00V
1μF 0805 50V
10μF 1206 6.3V
46.4k
AUX
975kHz
29.4k
1000kHz
28.0k
10.5V to 36V
8.00V
1μF 0805 50V
4.7μF 1206 10V
26.7k
AUX
1200kHz
23.7k
1600kHz
15.8k
13V to 36V
10.00V
1μF 0805 50V
4.7μF 0805 16V
21.0k
AUX
1250kHz
22.6k
2050kHz
10.5k
3.6V to 15V
0.82V
1μF 0805 50V
2 × 100μF 1206 6.3V
5.11M
VIN
500kHz
69.8k
600kHz
56.2k
3.6V to 15V
1.20V
1μF 0805 50V
100μF 1206 6.3V
475k
VIN
600kHz
56.2k
750kHz
42.2k
3.6V to 15V
1.80V
1μF 0805 50V
100μF 1206
191k
VIN
650kHz
51.1k
1000kHz
28.0k
3.6V to 15V
2.00V
1μF 0805 50V
100μF 1206
162k
VIN
650kHz
51.1k
1100kHz
26.7k
3.6V to 15V
2.50V
1μF 0805 50V
47μF 0805 6.3V
115k
VIN
700kHz
47.5k
1350kHz
20.5k
4.75V to 15V
3.30V
1μF 0805 50V
22μF 1206 6.3V
78.7k
AUX
950kHz
32.4k
1650kHz
15.0k
6.8V to 15V
5.00V
1μF 0805 50V
10μF 1206 6.3V
46.4k
AUX
1150kHz
25.5k
2400kHz
7.87k
10.5V to 15V
8.00V
1μF 0805 50V
4.7μF 1206 10V
26.7k
AUX
1200kHz
23.7k
2400kHz
7.87k
9V to 24V
0.82V
1μF 0805 50V
2 × 100μF 1206 6.3V
5.11M
≥2.8V, <25V
350kHz
105k
375kHz
93.1k
9V to 24V
1.20V
1μF 0805 50V
100μF//47μF 1206 6.3V
475k
≥2.8V, <25V
450kHz
78.7k
475kHz
73.2k
9V to 24V
1.80V
1μF 0805 50V
100μF 1206
191k
≥2.8V, <25V
600kHz
56.2k
650kHz
51.1k
9V to 24V
2.00V
1μF 0805 50V
100μF 1206
162k
≥2.8V, <25V
650kHz
51.1k
700kHz
47.5k
9V to 24V
2.50V
1μF 0805 50V
47μF 0805 6.3V
115k
≥2.8V, <25V
700kHz
47.5k
850kHz
37.4k
9V to 24V
3.30V
1μF 0805 50V
22μF 1206 6.3V
78.7k
AUX
950kHz
32.4k
1050kHz
28.0k
9V to 24V
5.00V
1μF 0805 50V
10μF 1206 6.3V
46.4k
AUX
1150kHz
25.5k
1550kHz
16.5k
10.5V to 24V
8.00V
1μF 0805 50V
4.7μF 1206 10V
26.7k
AUX
1200kHz
23.7k
2400kHz
7.87k
13V to 24V
10.00V
1μF 0805 50V
4.7μF 0805 16V
21.0k
AUX
1250kHz
22.6k
2400kHz
7.87k
Note: An input bulk capacitor is required.
8031fa
9
LTM8031
APPLICATIONS INFORMATION
may have only a small fraction of their nominal capacitance resulting in much higher output voltage ripple than
expected. Ceramic capacitors are also piezoelectric. In
Burst Mode operation, the LTM8031’s switching frequency
depends on the load current, and can excite a ceramic
capacitor at audio frequencies, generating audible noise.
Since the LTM8031 operates at a lower current limit during
Burst Mode operation, the noise is typically very quiet to a
casual ear. If this audible noise is unacceptable, use a high
performance electrolytic capacitor at the output. The input
capacitor can be a parallel combination of a 1μF ceramic
capacitor and a low cost electrolytic capacitor.
A final precaution regarding ceramic capacitors concerns
the maximum input voltage rating of the LTM8031. A
ceramic input capacitor combined with trace or cable
inductance forms a high Q (under damped) tank circuit.
If the LTM8031 circuit is plugged into a live supply, the
input voltage can ring to twice its nominal value, possibly exceeding the device’s rating. This situation is easily
avoided; see the Hot-Plugging Safely section.
Electromagnetic Compliance
The LTM8031 is compliant with the radiated emissions
requirements of EN55022 class B. Graphs of the LTM8031’s
EMC performance are given in the Typical Performance
Characteristics section. Further data, operating conditions
and test setup are detailed in an EMI Test report available
from Linear Technology.
Frequency Selection
The LTM8031 uses a constant frequency PWM architecture
that can be programmed to switch from 200kHz to 2.4MHz
by using a resistor tied from the RT pin to ground. Table 2
provides a list of RT resistor values and their resultant
frequencies.
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
LTM8031 is flexible enough to accommodate a wide range
Table 2. Switching Frequency vs RT Value
SWITCHING FREQUECNY (MHz)
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.2
1.4
1.5
1.8
2
2.2
2.4
RT VALUE (kΩ)
187
124
88.7
69.8
56.2
47.5
39.2
34
28.0
23.7
19.1
16.2
13.3
11.5
9.76
8.66
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
LTM8031 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 unnecessarily large output
capacitor. The maximum frequency (and attendant RT value)
at which the LTM8031 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.
BIAS Pin Considerations
The BIAS pin is used to provide drive power for the internal
power switching stage and operate internal circuitry. For
proper operation, it must be powered by at least 2.8V. If
the output voltage is programmed to be 2.8V or higher,
simply tie BIAS to AUX. If VOUT is less than 2.8V, BIAS
can be tied to VIN or some other voltage source. In all
cases, ensure that the maximum voltage at the BIAS pin
is both less than 25V and the sum of VIN and BIAS is less
8031fa
10
LTM8031
APPLICATIONS INFORMATION
than 56V. If BIAS power is applied from a remote or noisy
voltage source, it may be necessary to apply a decoupling
capacitor locally to the LTM8031.
Load Sharing
Two or more LTM8031s may be paralleled to produce higher
currents. This may, however, alter the EMI performance of
the LTM8031s. To do this, tie the VIN, ADJ, VOUT and SHARE
pins of all the paralleled LTM8031s together. To ensure that
paralleled modules start up together, the RUN/SS pins may
be tied together, as well. Synchronize the LTM8031s to an
external clock to eliminate beat frequencies, if required.
If the RUN/SS pins are not tied together, make sure that
the same valued soft-start capacitors are used for each
module. An example of two LTM8031 modules configured
for load sharing is given in the Typical Applications section. For 2A applications also see the LTM8032, 2A EMC
DC/DC μModule regulator
Characteristics section, it takes only about 3.6VIN for the
LTM8031 to run a 3.3V output at light load. If RUN/SS is
pulled up to VIN, it takes 5.7VIN to start. If the LTM8031
is enabled via the RUN/SS pin, the minimum voltage to
start at light loads is lower, about 4.4V. Similar curves for
2.5VOUT , 5VOUT and 8VOUT operation are also provided in
the Typical Performance Characteristics section.
Soft-Start
The RUN/SS pin can be used to soft-start the LTM8031,
reducing the maximum input current during start-up. The
RUN/SS pin is driven through an external RC network to
create a voltage ramp at this pin. Figure 1 shows the startup and shutdown waveforms with the soft-start circuit. By
choosing an appropriate RC time constant, the peak start-up
current can be reduced to the current that is required to
regulate the output, with no overshoot. Choose the value
of the resistor so that it can supply at least 20μA when
the RUN/SS pin reaches 2.5V.
Burst Mode Operation
To enhance efficiency at light loads, the LTM8031 automatically switches to Burst Mode operation which keeps
the output capacitor charged to the proper voltage while
minimizing the input quiescent current. During Burst Mode
operation, the LTM8031 delivers single cycle bursts of
current to the output capacitor followed by sleep periods
where the output power is delivered to the load by the output
capacitor. In addition, VIN and BIAS quiescent currents are
reduced to typically 20μA and 50μA respectively during
the sleep time. As the load current decreases towards a
no-load condition, the percentage of time that the LTM8031
operates in sleep mode increases and the average input
current is greatly reduced, resulting in higher efficiency.
Burst Mode operation is enabled by tying SYNC to GND. To
disable Burst Mode operation, tie SYNC to a stable voltage
above 0.7V. Do not leave the SYNC pin floating.
Minimum Input Voltage
The LTM8031 is a step-down converter, so a minimum
amount of headroom is required to keep the output in regulation. In addition, the input voltage required to turn on is
higher than that required to run, and depends upon whether
the RUN/SS is used. As shown in the Typical Performance
IL
0.5A/DIV
RUN
15k
RUN/SS
0.22μF
VRUN/SS
2V/DIV
GND
VOUT
2V/DIV
2ms/DIV
8031 F01
Figure 1. To Soft-Start the LTM8031, Add a Resistor
and Capacitor to the RUN/SS Pin
Synchronization
The internal oscillator of the LTM8031 can be synchronized by applying an external 250kHz to 2MHz clock to
the SYNC pin. Do not leave this pin floating. The resistor
tied from the RT pin to ground should be chosen such
that the LTM8031 oscillates 20% lower than the intended
synchronization frequency (see the Frequency Selection
section). The LTM8031 will not enter Burst Mode operation
while synchronized to an external clock, but will instead
skip pulses to maintain regulation.
8031fa
11
LTM8031
APPLICATIONS INFORMATION
Shorted Input Protection
operation with a haphazard or poor layout. See Figure 3
for a suggested layout.
Care needs to be taken in systems where the output will
be held high when the input to the LTM8031 is absent.
This may occur in battery charging applications or in
battery back-up systems where a battery or some other
supply is diode ORed with the LTM8031’s output. If the
VIN pin is allowed to float and the RUN/SS pin is held high
(either by a logic signal or because it is tied to VIN), then
the LTM8031’s internal circuitry will pull its quiescent
current through its internal power switch. This is fine if
your system can tolerate a few milliamps in this state. If
you ground the RUN/SS pin, the internal switch current
will drop to essentially zero. However, if the VIN pin is
grounded while the output is held high, then parasitic
diodes inside the LTM8031 can pull large currents from
the output through the VIN pin, potentially damaging the
device. Figure 2 shows a circuit that will run only when
the input voltage is present and that protects against a
shorted or reversed input.
Ensure that the grounding and heat sinking are acceptable.
A few rules to keep in mind are:
1. Place the RADJ 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 LTM8031. If a capacitor
is connected to the FIN terminals, place it as close
as possible to the FIN terminals, such that its ground
connection is as close as possible to that of the CIN
capacitor.
3. Place the COUT capacitor as close as possible to the
VOUT and GND connection of the LTM8031.
4. Place the CIN and COUT capacitors such that their
ground currents flow directly adjacent or underneath
the LTM8031.
5. 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 LTM8031.
PCB Layout
Most of the headaches associated with PCB layout have
been alleviated or even eliminated by the high level of
integration of the LTM8031. The LTM8031 is nevertheless 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
VIN
6. Use vias to connect the GND copper area to the board’s
internal ground plane. Liberally distribute these GND vias
to provide both a good ground connection and thermal
path to the internal planes of the printed circuit board.
VIN
VOUT
VOUT
RUN/SS
AUX
LTM8031
BIAS
ADJ
RT SYNC GND
8031 F02
Figure 2. The Input Diode Prevents a Shorted Input from Discharging
a Back-Up Battery Tied to the Output. It Also Protects the Circuit from
a Reversed Input. The LTM8031 Runs Only When the Input is Present
8031fa
12
LTM8031
PGOOD
RT
GND
RADJ
APPLICATIONS INFORMATION
COUT
SYNC
AUX
BIAS
RUN/SS
FIN
VIN
OPTIONAL
FIN
CAPACITOR
VOUT
CIN
GND
8031 F03
Figure 3. Layout Showing Suggested External Components,
GND Plane and Thermal Vias
circuit is connected to a 24V supply through six feet of 24gauge twisted pair. The first plot (4a) is the response with
a 2.2μF ceramic capacitor at the input. The input voltage
rings as high as 35V and the input current peaks at 20A.
One method of damping the tank circuit is to add another
capacitor with a series resistor to the circuit, as shown
in Figure 4b. A 0.7Ω resistor is added in series with the
input to eliminate the voltage overshoot (it also reduces
the peak input current). A 0.1μF capacitor improves high
frequency filtering. For high input voltages its impact on
efficiency is minor, reducing efficiency less than one-half
percent for a 5V output at full load operating from 24V.
By far the most popular method of controlling overshoot
is shown in Figure 4c, where an aluminum electrolytic
capacitor has been connected to FIN. This capacitor’s high
equivalent series resistance damps the circuit and eliminates the voltage overshoot. The extra capacitor improves
low frequency ripple filtering and can slightly improve the
efficiency of the circuit, though it is likely to be the largest
component in the circuit. Placing the electrolytic capacitor
at the FIN terminals can also improve the LTM8031’s EMI
filtering as well as guard against overshoots caused by
the Q of the integrated filter.
Hot-Plugging Safely
Thermal Considerations
The small size, robustness and low impedance of ceramic
capacitors make them an attractive option for the input
bypass capacitor of LTM8031. However, these capacitors
can cause problems if the LTM8031 is plugged into a live
or fast rising or falling supply (see Linear Technology
Application Note 88 for a complete discussion). The low
loss ceramic capacitor combined with stray inductance in
series with the power source forms an under-damped tank
circuit, and the voltage at the VIN pin of the LTM8031 can
ring to twice the nominal input voltage, possibly exceeding the LTM8031’s rating and damaging the part. A similar
phenomenon can occur inside the LTM8031 module, at the
output of the integrated EMI filter, with the same potential
of damaging the part.
The LTM8031 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 Characteristics section
can be used as a guide. These curves were generated by a
LTM8031 mounted to a 35cm2 4-layer FR4 printed circuit
board. Boards of other sizes and layer count 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.
If the input supply is poorly controlled or the user will be
plugging the LTM8031 into an energized supply, the input
network should be designed to prevent this overshoot. Figure 4 shows the waveforms that result when an LTM8031
The junction-to-air and junction-to-board thermal resistances given in the Pin Configuration diagram may also be
used to estimate the LTM8031 internal temperature. These
thermal coefficients are determined per JESD 51-9 (JEDEC
standard, test boards for area array surface mount package
thermal measurements) through analysis and physical
8031fa
13
LTM8031
APPLICATIONS INFORMATION
CLOSING SWITCH
SIMULATES HOT PLUG
IIN
DANGER
LTM8031
VIN
VIN
20V/DIV
RINGING VIN MAY EXCEED
ABSOLUTE MAXIMUM RATING
+
4.7μF
LOW
IMPEDANCE
ENERGIZED
24V SUPPLY
IIN
10A/DIV
STRAY
INDUCTANCE
DUE TO 6 FEET
(2 METERS) OF
TWISTED PAIR
20μs/DIV
(4a)
0.7Ω
LTM8031
VIN
VIN
20V/DIV
+
0.1μF
4.7μF
IIN
10A/DIV
(4b)
FIN
LTM8031
VIN
+
22μF
35V
AI.EI.
20μs/DIV
VIN
20V/DIV
+
4.7μF
IIN
10A/DIV
(4c)
20μs/DIV
8031 F04
Figure 4. A Well Chosen Input Network Prevents Input Voltage Overshoot and Ensures
Reliable Operation When the LTM8031 is Hot-Plugged to a Live Supply
correlation. Bear in mind that the actual thermal resistance
of the LTM8031 to the printed circuit board depends upon
the design of the circuit board. The die temperature of
the LTM8031 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 LTM8031.
The bulk of the heat flow out of the LTM8031 is through the
bottom of the module and the LGA 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.
Finally, be aware that at high ambient temperatures the
internal Schottky diode will have significant leakage current
increasing the quiescent current of the LTM8031.
8031fa
14
LTM8031
TYPICAL APPLICATIONS
0.82V Step-Down Converter
VIN*
3.6V TO 15V
OUT
VIN
1μF
FIN
LTM8031
VOUT
0.82V
200μF 1A
AUX
RUN/SS
BIAS
SHARE
PGOOD
RT SYNC GND ADJ
5.11M
69.8k
*RUNNING VOLTAGE RANGE.
SEE APPLICATIONS FOR START-UP DETAILS
8031 TA02
1.8V Step-Down Converter
VIN*
9V TO 24V
OUT
VIN
1μF
FIN
LTM8031
RUN/SS
VOUT
1.8V
100μF 1A
AUX
BIAS
SHARE
PGOOD
RT SYNC GND ADJ
56.2k
*RUNNING VOLTAGE RANGE.
SEE APPLICATIONS FOR START-UP DETAILS
191k
8031 TA03
8031fa
15
LTM8031
TYPICAL APPLICATIONS
2.5V Step-Down Converter
VIN*
3.6V TO 36V
1μF
FIN
LTM8031
22μF
VOUT
3.3V
1A
10μF
VOUT
5V
1A
AUX
RUN/SS
3.3V
47μF
VOUT
2.5V
1A
OUT
VIN
BIAS
SHARE
PGOOD
RT SYNC GND ADJ
115k
61.9k
8031 TA04
*RUNNING VOLTAGE RANGE.
SEE APPLICATIONS FOR START-UP DETAILS
3.3V Step-Down Converter
VIN*
4.75V TO 36V
OUT
VIN
LTM8031
FIN
AUX
RUN/SS
1μF
BIAS
SHARE
PGOOD
RT SYNC GND ADJ
48.7k
78.7k
*RUNNING VOLTAGE RANGE.
SEE APPLICATIONS FOR START-UP DETAILS
8031 TA08
5V Step-Down Converter
VIN*
6.8V TO 36V
OUT
VIN
FIN
LTM8031
RUN/SS
1μF
AUX
BIAS
SHARE
PGOOD
RT SYNC GND ADJ
29.4k
*RUNNING VOLTAGE RANGE.
SEE APPLICATIONS FOR START-UP DETAILS
46.4k
8031 TA05
8031fa
16
LTM8031
TYPICAL APPLICATIONS
8V Step-Down Converter
VIN*
10.5V TO 36V
OUT
VIN
FIN
4.7μF
LTM8031
VOUT
8V
1A
AUX
RUN/SS
1μF
BIAS
SHARE
PGOOD
RT SYNC GND ADJ
23.7k
26.7k
*RUNNING VOLTAGE RANGE.
SEE APPLICATIONS FOR START-UP DETAILS
8031 TA06
Two LTM8031s Operating in Parallel (Also See the LTM8032, 2A Pin Compatible)
VIN*
11.5V TO 36V
FIN
VOUT
8V
1.9A
OUT
VIN
LTM8031
AUX
RUN/SS
BIAS
1μF
SHARE
PGOOD
RT SYNC GND ADJ
23.7k
13.7k
OPTIONAL SYNC TIE TO
GND IF NOT USED
OUT
VIN
FIN
10μF
LTM8031
RUN/SS
AUX
BIAS
1μF
SHARE
PGOOD
RT SYNC GND ADJ
8031 TA07
23.7k
*RUNNING VOLTAGE RANGE.
SEE APPLICATIONS FOR START-UP DETAILS
8031fa
17
LTM8031
PACKAGE DESCRIPTION
LGA Package
71-Lead (15mm × 9mm × 2.82mm)
(Reference LTC DWG # 05-08-1823 Rev Ø)
2.670 – 2.970
7
aaa Z
6
5
4
3
2
1
PAD 1
Ø (0.635)
A
PAD 1
CORNER
B
4
C
D
E
15.00
BSC
12.700
BSC
F
G
H
MOLD
CAP
SUBSTRATE
J
0.27 – 0.37
K
1.270
BSC
Z
bbb Z
2.40 – 2.60
DETAIL A
L
PADS
SEE NOTES
X
aaa Z
9.00
BSC
Y
DETAIL A
PACKAGE SIDE VIEW
PACKAGE TOP VIEW
3
1.27
BSC
7.620
BSC
DETAIL A
PACKAGE BOTTOM VIEW
0.635 ±0.025 SQ. 71x
3.810
2.540
1.270
0.000
1.270
2.540
3.810
eee S X Y
6.350
DETAIL A
5.080
3.810
2.540
1.270
0.000
1.270
2.540
3.810
5.080
NOTES:
1. DIMENSIONING AND TOLERANCING PER ASME Y14.5M-1994
2. ALL DIMENSIONS ARE IN MILLIMETERS
3
LAND DESIGNATION PER JESD MO-222, SPP-010 AND SPP-020
4
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
LTMXXXXXX
μModule
COMPONENT
PIN 1
TRAY PIN 1
BEVEL
PACKAGE IN TRAY LOADING ORIENTATION
LGA 71 0108 REV Ø
5. PRIMARY DATUM -Z- IS SEATING PLANE
6. THE TOTAL NUMBER OF PADS: 71
SYMBOL TOLERANCE
aaa
0.15
bbb
0.10
eee
0.05
6.350
SUGGESTED PCB LAYOUT
TOP VIEW
8031fa
18
LTM8031
PACKAGE DESCRIPTION
Table 3. LTM8031 Pinout (Sorted by Pin Number)
PIN
SIGNAL DESCRIPTION
PIN
SIGNAL DESCRIPTION
A1
VOUT
F1
GND
A2
VOUT
F2
GND
A3
VOUT
F3
GND
A4
VOUT
F4
GND
A5
GND
F5
GND
A6
GND
F6
GND
A7
GND
F7
GND
B1
VOUT
G1
GND
B2
VOUT
G2
GND
B3
VOUT
G3
GND
B4
VOUT
G4
GND
B5
GND
G5
GND
B6
GND
G6
GND
B7
GND
G7
RT
C1
VOUT
H1
GND
C2
VOUT
H2
GND
C3
VOUT
H3
GND
C4
VOUT
H4
BIAS
C5
GND
H5
AUX
C6
GND
H6
GND
C7
GND
H7
SHARE
D1
VOUT
J5
GND
D2
VOUT
J6
GND
D3
VOUT
J7
ADJ
D4
VOUT
K1
VIN
D5
GND
K2
VIN
D6
GND
K3
FIN
D7
GND
K5
GND
E1
GND
K6
GND
E2
GND
K7
PGOOD
E3
GND
L1
VIN
E4
GND
L2
VIN
E5
GND
L3
FIN
E6
GND
L5
RUN/SS
E7
GND
L6
SYNC
L7
GND
8031fa
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.
19
LTM8031
PACKAGE PHOTOGRAPH
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTM4606
Ultralow Noise 6A DC/DC μModule Regulator
4.5V ≤ VIN ≤ 28V, 0.6V ≤ VOUT ≤ 5V, 15mm × 15mm × 2.8mm LGA
LTM4612
Ultralow Noise High VOUT DC/DC μModule Regulator
5A, 5V ≤ VIN ≤ 36V, 3.3V ≤ VOUT ≤ 15V, 15mm × 15mm × 2.8mm LGA
LTM8023
36V, 2A DC/DC μModule Regulator
3.6V ≤ VIN ≤ 36V, 0.8V ≤ VOUT ≤ 10V, 9mm × 11.75mm × 2.8mm LGA
LTM8025
36V, 3A DC/DC μModule Regulator
3.6V ≤ VIN ≤ 36V, 0.8V ≤ VOUT ≤ 24V, 9mm × 15mm × 4.32mm LGA
LTM8032
36V, 2A EMC DC/DC μModule Regulator
EN55022 Class B, 9mm × 15mm × 2.8mm LGA. Pin Compatible with the
LTM8031
8031fa
20 Linear Technology Corporation
LT 1009 • PRINTED IN USA
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