LTM8046 - 3.1VIN to 31VIN, 2kVAC Isolated DC/DC μModule Converter

LTM8046
3.1VIN to 31VIN, 2kVAC
Isolated DC/DC µModule
Converter
Features
Description
2kVAC Isolated µModule Converter (Tested to 3kVDC)
n UL 60950 Recognized
, File E464570
n Wide Input Voltage Range: 3.1V to 31V
n5V at 550mA from 24V
IN
n1.8V to 12V Output Voltage
n Current Mode Control
n Programmable Soft-Start
n User Configurable Undervoltage Lockout
n SnPb or RoHS Compliant Finish
n9mm × 15mm × 4.92mm BGA Package
The LTM®8046 is an isolated flyback DC/DC µModule®
(micromodule) converter. The LTM8046 has an isolation
rating of 2kVAC. Included in the package are the switching
controller, power switches, transformer, and all support
components. Operating over an input voltage range of 3.1V
to 31V, the LTM8046 supports an output voltage range
of 1.8V to 12V, set by one resistor. Only output, input,
and bias capacitors are needed to finish the design. An
optional capacitor can be used to set the soft-start period.
n
®
Applications
Industrial Sensors
Industrial Switches
n Ground Loop Mitigation
n
n
The LTM8046 is packaged in a 9mm × 15mm × 4.92mm
over-molded ball grid array (BGA) package suitable for
automated assembly by standard surface mount equipment. The LTM8046 is available with SnPb (BGA) or RoHS
compliant terminal finish.
L, LT, LTC, LTM, Linear Technology, the Linear logo and µModule are registered trademarks of
Linear Technology Corporation. All other trademarks are the property of their respective owners.
Typical Application
Maximum Output Current vs VIN
2kV Isolated Low Noise µModule Regulator
VIN
RUN
BIAS
1µF
8.45k
FB
SS
GND
ISOLATION BARRIER
1µF
VOUT
5V
VOUT
100µF
VOUT–
2kVAC ISOLATION
8046 TA01a
MAXIMUM OUTPUT CURRENT (mA)
LTM8046
VIN
4.3V TO 26V
700
600
500
400
300
200
100
0
5
10
15
VIN (V)
20
25
30
8046 TA01b
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1
LTM8046
Absolute Maximum Ratings
Pin Configuration
(Note 1)
TOP VIEW
VIN, RUN....................................................................32V
FB, SS..........................................................................5V
VOUT Relative to VOUT–...............................................16V
VIN + 2VOUT (Note 5)..................................................36V
BIAS................................................................. VIN + 0.1V
GND to VOUT– Isolation (Note 2)............................2kVAC
Maximum Internal Temperature (Note 3)............... 125°C
Peak Solder Reflow Body Temperature.................. 245°C
A
BANK 4
VOUT B
C
BANK 3
VOUT–
D
E
F
G
H
BANK 2
GND
J
BANK 1
VIN K
L
RUN BIAS SS
1
2
3
4
5
FB
6
7
BGA PACKAGE
51-LEAD (15mm × 9mm × 4.92mm)
TJMAX = 125°C, θJA = 21.9°C/W, θJCbottom = 7.9°C/W, θJCtop = 17.9°C/W, θJB = 8.4°C/W
WEIGHT = 1.5g, θ VALUES DETERMINED PER JEDEC 51-9, 51-12
Order Information
PART NUMBER
PAD OR BALL FINISH
PART MARKING*
DEVICE
FINISH CODE
PACKAGE
TYPE
MSL
RATING
TEMPERATURE RANGE
(See Note 3)
LTM8046EY#PBF
SAC305 (RoHS)
LTM8046Y
e1
BGA
3
–40°C to 125°C
LTM8046IY#PBF
SAC305 (RoHS)
LTM8046Y
e1
BGA
3
–40°C to 125°C
LTM8046IY
SnPb (63/37)
LTM8046Y
e0
BGA
3
–40°C to 125°C
LTM8046MPY#PBF
SAC305 (RoHS)
LTM8046Y
e1
BGA
3
–55°C to 125°C
LTM8046MPY
SnPb (63/37)
LTM8046Y
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.
• Recommended LGA and BGA PCB Assembly and Manufacturing
Procedures:
www.linear.com/umodule/pcbassembly
• Pb-free and Non-Pb-free Part Markings:
www.linear.com/leadfree
• LGA and BGA Package and Tray Drawings:
www.linear.com/packaging
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LTM8046
Electrical
Characteristics
The l denotes the specifications which apply over the full internal
operating temperature range, otherwise specifications are at TA = 25°C, RUN = 12V (Note 3).
PARAMETER
CONDITIONS
Minimum Input DC Voltage
BIAS = VIN, VRUN = 2V
BIAS Open, VRUN = 2V
l
l
MIN
VOUT DC Voltage
RFB = 14.7k
RFB = 8.45k
RFB = 3.83k
l
4.75
TYP
2.5
5
12
MAX
UNITS
3.1
4.3
V
V
5.25
V
V
V
1
µA
VIN Quiescent Current
VRUN = 0V
VOUT Line Regulation
6V ≤ VIN ≤ 31V, IOUT = 0.15A, VRUN = 2V
1
%
VOUT Load Regulation
0.05A ≤ IOUT ≤ 0.4A, VRUN = 2V
1.5
%
VOUT Ripple (RMS)
IOUT = 0.1A, BW = 1MHz
20
mV
Isolation Test Voltage
(Note 2)
Input Short Circuit Current
VOUT Shorted
3000
RUN Pin Input Threshold
VRUN Pin Rising
RUN Pin Current
VRUN = 1V
VRUN = 1.3V
VDC
30
1.18
SS Threshold
1.24
1.30
V
2.5
0.1
µA
µA
0.7
V
µA
SS Sourcing Current
SS = 0V
–8
BIAS Current
VIN = 12V, BIAS = 5V, IOUT = 100mA
10
Minimum BIAS Voltage (Note 4)
IOUT = 100mA
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 LTM8046 isolation is tested at 3kVDC for one second.
Note 3: The LTM8046E is guaranteed to meet performance specifications
from 0°C to 125°C. Specifications over the –40°C to 125°C internal
temperature range are assured by design, characterization and correlation
with statistical process controls. LTM8046I is guaranteed to meet
specifications over the full –40°C to 125°C internal operating temperature
range. The LTM8046MP 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.
mA
mA
3.1
V
Note 4: This is the BIAS pin voltage at which the internal circuitry is
powered through the BIAS pin and not the integrated regulator. See BIAS
Pin Considerations for details.
Note 5: VIN + 2VOUT is defined as the sum of the voltage between (VIN –
GND) added to twice the voltage between (VOUT – VOUT–).
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3
LTM8046
Typical Performance Characteristics
1.8VOUT Efficiency vs Output
Current
5VIN
65
12VIN
24VIN
60
55
75
5VIN
5VIN
70
12VIN
65
24VIN
60
55
50
45
BIAS = 3.3V
70
EFFICIENCY (%)
70
EFFICIENCY (%)
75
BIAS = 3.3V
0
200
400
600
OUTPUT CURRENT (mA)
50
800
0
100
200 300 400 500
OUTPUT CURRENT (mA)
600
BIAS = 3.3V
12VIN
75
5VIN
24VIN
EFFICIENCY (%)
70
60
50
700
65
60
BIAS = 3.3V
0
100
200 300 400 500
OUTPUT CURRENT (mA)
12VOUT Efficiency vs Output
Current
80
12VIN
5VIN
BIAS = 3.3V
75
70
20VIN
70
700
600
8046 G03
EFFICIENCY (%)
75
24VIN
8VOUT Efficiency vs Output
Current
80
BIAS = 3.3V
65
8046 G02
5VOUT Efficiency vs Output
Current
80
12VIN
55
8046 G01
EFFICIENCY (%)
3.3VOUT Efficiency vs Output
Current
EFFICIENCY (%)
75
2.5VOUT Efficiency vs Output
Current
65
60
5VIN
65
60
12VIN
55
50
55
0
200
400
OUTPUT CURRENT (mA)
50
600
45
0
8046 G04
5VIN
12VIN
100
50
300
150
12VIN
100
24VIN
50
0
200
600
400
OUTPUT CURRENT (mA)
800
8046 G07
100
150
200
OUTPUT CURRENT (mA)
0
250
BIAS = 3.3V
250
5VIN
5VIN
200
12VIN
150
100
24VIN
50
24VIN
0
50
3.3VOUT Input Current vs Output
Current
BIAS = 3.3V
200
INPUT CURRENT (mA)
INPUT CURRENT (mA)
250
150
0
8046 G06
2.5VOUT Input Current vs Output
Current
BIAS = 3.3V
200
40
500
8046 G05
1.8VOUT Input Current vs Output
Current
250
100
300
400
200
OUTPUT CURRENT (mA)
INPUT CURRENT (mA)
50
55
0
200
400
600
OUTPUT CURRENT (mA)
800
8046 G08
0
0
200
400
600
OUTPUT CURRENT (mA)
400
8046 G09
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LTM8046
Typical Performance Characteristics
350
400
BIAS = 3.3V
12VIN
200
150
24VIN
100
200
20VIN
150
100
0
800
0
100
200
300
400
OUTPUT CURRENT (mA)
14
5VIN
9
0
500
12VIN
8
24VIN
7
6
0
50
100
150
200
OUTPUT CURRENT (mA)
250
8046 12
3.3VOUT Bias Current vs Output
Current
13
BIAS = 3.3V
11
12VIN
10
8
24VIN
6
BIAS = 3.3V
5VIN
12
5VIN
12
BIAS CURRENT (mA)
4
12VIN
10
9
24VIN
8
7
6
5
2
4
0
0
200
400
600
OUTPUT CURRENT (mA)
800
5
0
200
400
600
OUTPUT CURRENT (mA)
12
16
5VIN
12VIN
BIAS CURRENT (mA)
24VIN
10
8
6
4
2
0
200
400
OUTPUT CURRENT (mA)
600
8046 G16
16
13
11
20VIN
10
9
13
5VIN
11
10
9
8
7
7
0
700
100
200
300
400
OUTPUT CURRENT (mA)
500
8046 G17
12VIN
12
8
6
600
14
12VIN
12
BIAS = 3.3V
15
5VIN
14
200 300 400 500
OUTPUT CURRENT (mA)
12VOUT Bias Current vs Output
Current
BIAS = 3.3V
15
100
8046 G15
8VOUT Bias Current vs Output
Current
5VOUT Bias Current vs Output
Current
BIAS = 3.3V
0
8046 G14
8046 G13
14
4
800
BIAS CURRENT (mA)
BIAS CURREBT (mA)
100
2.5VOUT Bias Current vs Output
Current
BIAS = 3.3V
10
BIAS CURRENT (mA)
150
8046 G11
1.8VOUT Bias Current vs Output
Current
0
200
50
8046 G10
11
12VIN
250
BIAS CURRENT (mA)
200
400
OUTPUT CURRENT (mA)
5VIN
300
50
0
BIAS = 3.3V
350
12VIN
250
50
0
400
5VIN
300
INPUT CURRENT (mA)
250
12VOUT Input Current vs Output
Current
BIAS = 3.3V
350
5VIN
300
INPUT CURRENT (mA)
8VOUT Input Current vs Output
Current
INPUT CURRENT (mA)
5VOUT Input Current vs Output
Current
6
0
50
100
150
200
OUTPUT CURRENT (mA)
250
8046 G18
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5
LTM8046
Typical Performance Characteristics
Maximum Output Current vs VIN
Maximum Output Current vs VIN
600
700
600
500
400
1.8VOUT
2.5VOUT
3.3VOUT
300
10
20
VIN (V)
7
MINIMUM LOAD (mA)
MINIMUM LOAD (mA)
5
4
3
2
8VOUT
10
20
VIN (V)
TEMPERATURE RISE (°C)
20
200
5VOUT
8VOUT
12VOUT
100
0
3
9
12 15
VIN (V)
18
21
10
0
8
16
VIN (V)
24
32
8046 G21
Input Current vs VIN Output
Shorted
BIAS = 3.3V
80
60
40
20
0
4
8
12
VIN (V)
3.3VIN
5VIN
12VIN
24VIN
800
0
0
10
20
VIN (V)
8046 G23
20
10
200
400
600
OUTPUT CURRENT (mA)
1.8VOUT
2.5VOUT
3.3VOUT
100
8046 G22
5
10
120
BIAS = 3.3V
15
0
15
0
27
5
30
20
8046 G20
Temperature Rise vs Output
Current 2.5VOUT
0
24
12VOUT Minimum Load vs VIN
15
0
6
25
5
20
5VOUT
0
300
25
BIAS = 3.3V
6
0
400
8046 G19
Minimum Load vs VIN
1
500
0
30
BIAS = 3.3V
30
INPUT CURRENT (mA)
0
BIAS = 3.3V
TEMPERATURE RISE (°C)
200
Minimum Load vs VIN
35
MINIMUM LOAD (mA)
BIAS = 3.3V
MAXIMUM OUTPUT CURRENT (mA)
MAXIMUM OUTPUT CURRENT (mA)
800
30
40
8046 G24
Temperature Rise vs Output
Current 3.3VOUT
15
10
3.3VIN
5VIN
12VIN
24VIN
5
0
0
8046 G25
200
400
600
OUTPUT CURRENT (mA)
800
8046 G26
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LTM8046
Typical Performance Characteristics
10
3.3VIN
5VIN
12VIN
24VIN
0
0
100
200 300 400 500
OUTPUT CURRENT (mA)
600
700
TEMPERATURE RISE (°C)
15
5
20
15
TEMPERATURE RISE (°C)
TEMPERATURE RISE (°C)
20
Temperature Rise vs Output
Current 8VOUT
Temperature Rise vs Output
Current 5VOUT
10
5
0
3.3VIN
5VIN
12VIN
0
100
200
300
OUTPUT CURRENT (mA)
8046 G27
400
Temperature Rise vs Output
Current 12VOUT
15
10
5
0
3.3VIN
5VIN
12VIN
0
100
200
OUTPUT CURRENT (mA)
8046 G29
8046 G28
Output Ripple
300
Step Input Start-Up Waveform
NO CSS
1V/
DIV
50mV/
DIV
CSS = 0.1µF
CSS = 0.033µF
2µs/DIV
24VIN, 5VOUT
570mA LOAD
DC1559A DEMO BOARD
UNMODIFIED
150MHz BW
8046 G30
200µs/DIV
24VIN, 5VOUT
20Ω RESISTIVE LOAD
8046 G31
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7
LTM8046
Pin Functions
VIN (Bank 1): VIN supplies current to the LTM8046’s
internal regulator and to the integrated power switch.
These pins must be locally bypassed with an external,
low ESR capacitor.
GND (Bank 2): This is the primary side local ground of
the LTM8046 primary. In most applications, the bulk of
the heat flow out of the LTM8046 is through the GND and
VOUT– 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.
VOUT–
VOUT–
–
(Bank 3): VOUT is the return for VOUT. VOUT and
comprise the isolated output of the LTM8046. In
most applications, the bulk of the heat flow out of the
LTM8046 is through the GND and VOUT– 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. Apply an external
capacitor between VOUT and VOUT–.
VOUT (Bank 4): VOUT and VOUT– comprise the isolated
output of the LTM8046 flyback stage. Apply an external
capacitor between VOUT and VOUT–. Do not allow VOUT– to
exceed VOUT.
RUN (Pin L3): A resistive divider connected to VIN and this
pin programs the minimum voltage at which the LTM8046
will operate. Below 1.24V, the LTM8046 does not deliver
power to the secondary. Above 1.24V, power will be delivered to the secondary and 8µA will be fed into the SS
pin. When RUN is less than 1.24V, the pin draws 2.5µA,
allowing for a programmable hysteresis. Do not allow a
negative voltage (relative to GND) on this pin.
BIAS (Pin L4): This pin supplies the power necessary to
operate the LTM8046. It must be locally bypassed with
a low ESR capacitor of at least 1μF. Do not allow this pin
voltage to rise above VIN.
SS (Pin L5): Place a soft-start capacitor here to limit inrush
current and the output voltage ramp rate. Do not allow a
negative voltage (relative to GND) on this pin.
FB (Pin L6): Apply a resistor from this pin to GND to set
the output voltage, using the recommended value given
in Table 1. If Table 1 does not list the desired VOUT value,
the equation
(
)
RFB = 31.6 VOUT –0.84 kΩ
may be used to approximate the value. To the seasoned
designer, this exponential equation may seem unusual.
The equation is exponential due to non-linear current
sources that are used to temperature compensate the
output regulation.
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LTM8046
Block Diagram
VOUT
VIN
•
•
0.1µF
1µF
RUN
BIAS*
SS
VOUT–
CURRENT
MODE
CONTROLLER
FB
GND
8046 BD
*DO NOT ALLOW BIAS VOLTAGE TO EXCEED VIN
Operation
The LTM8046 is a stand-alone isolated flyback switching
DC/DC µModule converter that can deliver over 700mA of
output current. This module provides a regulated output
voltage programmable via one external resistor from 1.8V
to 12V. The input voltage range of the LTM8046 is 3.1V
to 31V. Given that the LTM8046 is a flyback converter,
the output current depends upon the input and output
voltages, so make sure that the input voltage is high
enough to support the desired output voltage and load
current. The Typical Performance Characteristics section
gives several graphs of the maximum load versus VIN for
several output voltages.
A simplified block diagram is given. The LTM8046 contains
a current mode controller, power switching element, power
transformer, power Schottky diode, a modest amount of
input and output capacitance.
The LTM8046 has a galvanic primary to secondary isolation rating of 2kVAC. This is verified by applying 3kVDC
between the primary to secondary for 1 second. Note
that the 2kVAC isolation is verified by a 3kVDC test. This
is because the 2kVAC waveform has a peak voltage 1.414
times higher than 2kV, or 2.83kVDC. For the LTM8046, at
least 3kVDC is applied. For further details please refer to
the Isolation and Working Voltage section.
An internal regulator provides power to the control circuitry. The bias regulator normally draws power from the
VIN pin, but if the BIAS pin is connected to an external
voltage higher than 3.1V, bias power will be drawn from
the external source, improving efficiency. VBIAS must not
exceed VIN. The RUN pin is used to turn on or off the
LTM8046, disconnecting the output and reducing the
input current to 1μA or less.
The LTM8046 is a variable frequency device. For a fixed
input and output voltage, the frequency decreases as
the load increases. For light loads, the current through
the internal transformer may be discontinuous, so that
frequency may appear to decrease. Note that a minimum
load is required to keep the output voltage in regulation.
Refer to the Typical Performance Characteristics section.
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9
LTM8046
Applications Information
For most applications, the design process is straightforward, 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 and RFB.
3.Connect BIAS as indicated, or tie to an external source
up to 15V or VIN, whichever is less.
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 may be limited by junction temperature,
the relationship between the input and output voltage
magnitude and polarity and other factors. Please refer
to the graphs in the Typical Performance Characteristics
section for guidance.
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 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 LTM8046. A
ceramic input capacitor combined with trace or cable
inductance forms a high-Q (underdamped) tank circuit. If
the LTM8046 circuit is plugged into a live supply, the input
voltage can ring to much higher than its nominal value,
possibly exceeding the device’s rating. This situation is
easily avoided; see the Hot-Plugging Safely section.
Table 1. Recommended Components and Configuration (TA = 25°C)
VIN
VOUT
CIN
COUT
RFB
3.2V to 32V
1.8V
1µF, 50V, 0805 X5R
2 × 100µF, 6.3V, 1206 X5R
18.7k
3.2V to 31V
2.5V
1µF, 50V, 0805 X5R
2 × 100µF, 6.3V, 1206 X5R
14.7k
3.2V to 29V
3.3V
1µF, 50V, 0805 X5R
100µF, 6.3V, 1206 X5R
11.8k
3.2V to 26V
5V
1µF, 25V, 0603 X5R
100µF, 6.3V, 1206 X5R
8.45k
3.2V to 20V
8V
1µF, 25V, 0603 X5R
47µF, 10V, 1206 X5R
5.49k
3.2V to 12V
12V
1µF, 25V, 0603 X5R
2 × 10µF, 16V, 1210 X5R
3.83k
3.2V to 25V
2.5V
1µF, 25V, 0603 X5R
2 × 100µF, 6.3V, 1206 X5R
14.7k
3.2V to 25V
3.3V
1µF, 25V, 0603 X5R
100µF, 6.3V, 1206 X5R
11.8k
CBIAS = 1µF 10V 0402 X5R
BIAS = 3.3V for VIN ≥ 3.3V, VIN for VIN < 3.3V. If BIAS = VIN, the minimum input voltage is 4.3V.
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LTM8046
Applications Information
BIAS Pin Considerations
The BIAS pin is the output of an internal linear regulator
that powers the LTM8046’s internal circuitry. It is set to
3V and must be decoupled with a low ESR capacitor of at
least 1μF. The LTM8046 will run properly without applying a voltage to this pin, but will operate more efficiently
and dissipate less power if a voltage greater than 3.1V is
applied. At low VIN, the LTM8046 will be able to deliver
more output current if BIAS is 3.1V or greater. Up to 31V
may be applied to this pin, but a high BIAS voltage will
cause excessive power dissipation in the internal circuitry.
For applications with an input voltage less than 15V, the
BIAS pin is typically connected directly to the VIN pin. For
input voltages greater than 15V, it is preferred to leave the
BIAS pin separate from the VIN pin, either powered from
a separate voltage source or left running from the internal
regulator. This has the added advantage of keeping the
physical size of the BIAS capacitor small. Do not allow
BIAS to rise above VIN.
Soft-Start
For many applications, it is necessary to minimize the
inrush current at start-up. The built-in soft-start circuit
significantly reduces the start-up current spike and output voltage overshoot by applying a capacitor from SS to
GND. When the LTM8046 is enabled, whether from VIN
reaching a sufficiently high voltage or RUN being pulled
high, the LTM8046 will source approximately 8µA out of
the SS pin. As this current gradually charges the capacitor from SS to GND, the LTM8046 will correspondingly
increase the power delivered to the output, allowing for a
graceful turn-on ramp.
Isolation Working Voltage and Safety
The LTM8046 isolation is 100% hi-pot tested by tying
all of the primary pins together, all of the secondary pins
together and subjecting the two resultant circuits to a
differential of 3kVDC for one second. This establishes
the isolation voltage rating of the LTM8046 component.
The isolation rating of the LTM8046 is not the same as
the working or operational voltage that the application
will experience. This is subject to the application’s power
source, operating conditions, the industry where the end
product is used and other factors that dictate design
requirements such as the gap between copper planes,
traces and component pins on the printed circuit board,
as well as the type of connector that may be used. To
maximize the allowable working voltage, the LTM8046 has
three rows of solder balls removed to facilitate the printed
circuit board design. The ball to ball pitch is 1.27mm,
and the typical ball diameter is 0.78mm. Accounting for
the missing row and the ball diameter, the printed circuit
board may be designed for a metal-to-metal separation
of up to 4.3mm. This may have to be reduced somewhat
to allow for tolerances in solder mask or other printed
circuit board design rules.
To reiterate, the manufacturer’s isolation voltage rating
and the required operational voltage are often different
numbers. In the case of the LTM8046, the isolation voltage
rating is established by 100% hi-pot testing. The working
or operational voltage is a function of the end product
and its system level specifications. The actual required
operational voltage is often smaller than the manufacturer’s
isolation rating.
For those situations where information about the spacing
of LTM8046 internal circuitry is required, the minimum
metal to metal separation of the primary and secondary is
1.9mm. The LTM8046 is a UL recognized component under
UL 60950-1, file number E464570. The UL 60950-1 insulation category of the LTM8046 transformer is Functional.
Considering UL 60950-1 Table 2N and the gap distances
stated above, 4.3mm external and 1.9mm internal, the
LTM8046 may be operated with up to 400V working
voltage in a pollution degree 2 environment. The actual
working voltage, insulation category, pollution degree and
other critical parameters for the specific end application
depend upon the actual environmental, application and
safety compliance requirements. It is therefore up to the
user to perform a safety and compliance review to ensure
that the LTM8046 is suitable for the intended application.
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For more information www.linear.com/LTM8046
11
LTM8046
Applications Information
VOUT to VOUT– Reverse Voltage
VOUT–
The LTM8046 cannot tolerate a reverse voltage from VOUT
to VOUT– during operation. If VOUT– raises above VOUT during operation, the LTM8046 may be damaged. To protect
against this condition, a low forward drop power Schottky
diode has been integrated into the LTM8046, anti-parallel
to VOUT/VOUT–. This can protect the output against many
reverse voltage faults. Reverse voltage faults can be both
steady state and transient. An example of a steady state
voltage reversal is accidentally misconnecting a powered
LTM8046 to a negative voltage source. An example of
transient voltage reversals is a momentary connection to
a negative voltage. It is also possible to achieve a VOUT
reversal if the load is short-circuited through a long cable.
The inductance of the long cable forms an LC tank circuit
with the VOUT capacitance, which drives VOUT negative.
Avoid these conditions.
Minimum Load
GND
FB
SS
BIAS
RUN
VOUT
THERMAL/INTERCONNECT VIAS
VIN
GND
8046 F01
Figure 1. Layout Showing Suggested External Components,
Planes and Thermal Vias
Figure 1 for a suggested layout. Ensure that the grounding
and heat sinking are acceptable.
The LTM8046 requires a minimum load in order to maintain regulation. If less than the minimum load is applied,
the output voltage may rise beyond the intended value
uncontrollably, possibly damaging the LTM8046 or the
application system. Avoid this situation. The Typical
Performance Characteristics section provides graphs of
the minimum required load for several input and output
conditions at room temperature.
A few rules to keep in mind are:
The LTM8046 is designed to skip switching cycles, if
necessary, to maintain regulation. While cycle skipping,
the output ripple may be higher than when the LTM8046
is not skipping cycles. The user must validate the performance of the LTM8046 application over the appropriate
temperature, line, load and other operating conditions.
4.Place the CIN and COUT capacitors such that their
ground current flow directly adjacent or underneath
the LTM8046.
1.Place the RADJ resistor as close as possible to its respective pin.
2.Place the CIN capacitor as close as possible to the VIN
and GND connections of the LTM8046.
3.Place the COUT capacitor as close as possible to VOUT
and VOUT–.
PCB Layout
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 LTM8046.
Most of the headaches associated with PCB layout have
been alleviated or even eliminated by the high level of
integration of the LTM8046. The LTM8046 is nevertheless a switching power supply, and care must be taken to
minimize electrical noise to ensure proper operation. Even
with the high level of integration, you may fail to achieve
specified operation with a haphazard or poor layout. See
6.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 1. The LTM8046 can benefit from
the heat sinking afforded by vias that connect to internal
8046fb
12
For more information www.linear.com/LTM8046
LTM8046
Applications Information
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.
The printed circuit board construction has an impact on
the isolation performance of the end product. For example,
increased trace and layer spacing, as well as the choice
of core and prepreg materials (such as using polyimide
versus FR4) can significantly affect the isolation withstand
of the end product.
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 LTM8046. However, these capacitors can cause problems if the LTM8046 is plugged into a
live 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 underdamped tank circuit, and the voltage at the VIN pin of the LTM8046 can ring to more than
twice the nominal input voltage, possibly exceeding the
LTM8046’s rating and damaging the part. If the input
supply is poorly controlled or the user will be plugging
the LTM8046 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
to VIN, but the most popular method of controlling input
voltage overshoot is adding an electrolytic bulk capacitor
to VIN. This capacitor’s relatively 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 can be a large component in the circuit.
Thermal Considerations
The LTM8046 output current may need to be derated if it
is required to operate in a high ambient temperature. 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 the LTM8046 mounted to a 58cm2
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.
For increased accuracy and fidelity to the actual application,
many designers use FEA to predict thermal performance.
To that end, the Pin Configuration section of the data sheet
typically 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 as follows:
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 junction-to-board thermal resistance 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.
8046fb
For more information www.linear.com/LTM8046
13
LTM8046
Applications Information
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 junction 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.
be inappropriate to attempt to use any one coefficient to
correlate to the junction temperature vs 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.
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 two-sided,
two-layer board. This board is described in JESD 51-9.
The blue resistances are contained within the µModule
converter, and the green are outside.
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
A graphical representation of these thermal resistances
is given in Figure 2.
The die temperature of the LTM8046 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
LTM8046. The bulk of the heat flow out of the LTM8046
is through the bottom of the module 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.
JUNCTION-TO-AMBIENT RESISTANCE (JESD 51-9 DEFINED BOARD)
JUNCTION-TO-CASE (TOP)
RESISTANCE
JUNCTION
CASE (TOP)-TO-AMBIENT
RESISTANCE
JUNCTION-TO-BOARD RESISTANCE
CASE (BOTTOM)-TO-BOARD
JUNCTION-TO-CASE
RESISTANCE
(BOTTOM) RESISTANCE
AMBIENT
BOARD-TO-AMBIENT
RESISTANCE
8046 F02
µMODULE DEVICE
Figure 2.
8046fb
14
For more information www.linear.com/LTM8046
LTM8046
Typical Applications
3.3V Isolated Flyback Converter
LTM8046
VIN
3.3V TO 29V
VIN
3.3V
BIAS
1µF
11.8k
FB
SS
ISOLATION BARRIER
RUN
1µF
VOUT
3.3V
VOUT
100µF
VOUT–
GND
2kVAC ISOLATION
8046 TA02a
Maximum Output Current vs VIN
MAXIMUM OUTPUT CURRENT (mA)
800
700
600
500
400
300
200
0
10
20
VIN (V)
30
8046 TA02b
8046fb
For more information www.linear.com/LTM8046
15
LTM8046
Typical Applications
Use Two LTM8046 Flyback Converters to Generate ±5V
LTM8046
VIN
4.3V TO 26V
1µF
VIN
BIAS
8.45k
FB
SS
1µF
ISOLATION BARRIER
RUN
1µF
5V
VOUT
100µF
VOUT–
GND
2kVAC ISOLATION
22µF
LTM8046
VIN
RUN
BIAS
1µF
8.45k
FB
SS
1µF
ISOLATION BARRIER
1µF
VOUT
100µF
VOUT–
GND
–5V
2kVAC ISOLATION
8046 TA03a
Maximum Output Current vs VIN
MAXIMUM OUTPUT CURRENT (mA)
700
600
500
400
300
200
100
0
5
10
15
VIN (V)
20
25
30
8046 TA03b
8046fb
16
For more information www.linear.com/LTM8046
LTM8046
Package Description
Pin Assignment Table
(Arranged by Pin Number)
PIN NAME
A1 VOUT
A2 VOUT
A3 VOUT
A4 VOUT
A5 VOUT–
A6 VOUT–
A7 VOUT–
PIN NAME
B1 VOUT
B2 VOUT
B3 VOUT
B4 VOUT
B5 VOUT–
B6 VOUT–
B7 VOUT–
PIN NAME
C1 VOUT–
C2 VOUT–
C3 VOUT–
C4 VOUT–
C5 VOUT–
C6 VOUT–
C7 VOUT–
PIN NAME
D1D2D3D4D5D6D7-
PIN NAME
E1E2E3E4E5E6E7-
PIN NAME
F1F2F3F4F5F6F7-
PIN NAME
G1 GND
G2 GND
G3 GND
G4 GND
G5 GND
G6 GND
G7 GND
PIN NAME
H1H2H3 GND
H4 GND
H5 GND
H6 GND
H7 GND
PIN NAME
J1 VIN
J2J3 GND
J4 GND
J5 GND
J6 GND
J7 GND
PIN NAME
K1 VIN
K2K3 GND
K4 GND
K5 GND
K6 GND
K7 GND
PIN NAME
L1 VIN
L2L3 RUN
L4 BIAS
L5 SS
L6 FB
L7 GND
Package Photo
8046fb
For more information www.linear.com/LTM8046
17
0.630 ±0.025 Ø 51x
SUGGESTED PCB LAYOUT
TOP VIEW
2.540
PACKAGE TOP VIEW
1.270
4
0.3175
0.000
0.3175
PIN “A1”
CORNER
E
1.270
aaa Z
2.540
18
Y
For more information www.linear.com/LTM8046
6.350
5.080
3.810
2.540
1.270
0.000
3.810
5.080
6.350
D
X
aaa Z
// bbb Z
SYMBOL
A
A1
A2
b
b1
D
E
e
F
G
H1
H2
aaa
bbb
ccc
ddd
eee
H1
SUBSTRATE
NOM
4.92
0.60
4.32
0.78
0.63
15.00
9.00
1.27
12.70
7.62
0.32
4.00
A
A2
MAX
5.12
0.70
4.42
0.85
0.66
NOTES
DETAIL B
PACKAGE SIDE VIEW
0.37
4.05
0.15
0.10
0.20
0.30
0.15
TOTAL NUMBER OF BALLS: 51
0.27
3.95
MIN
4.72
0.50
4.22
0.71
0.60
b1
DIMENSIONS
ddd M Z X Y
eee M Z
DETAIL A
Øb (51 PLACES)
DETAIL B
H2
MOLD
CAP
ccc Z
A1
Z
(Reference LTC DWG# 05-08-1889 Rev Ø)
Z
b
3
F
e
SEE NOTES
7
5
4
3
2
1
DETAIL A
PACKAGE BOTTOM VIEW
6
G
L
K
J
H
G
F
E
D
C
B
A
PIN 1
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
BALL DESIGNATION PER JESD MS-028 AND JEP95
TRAY PIN 1
BEVEL
BGA 51 1110 REV Ø
PACKAGE IN TRAY LOADING ORIENTATION
LTMXXXXXX
µModule
6. SOLDER BALL COMPOSITION CAN BE 96.5% Sn/3.0% Ag/0.5% Cu
OR Sn Pb EUTECTIC
5. PRIMARY DATUM -Z- IS SEATING PLANE
4
3
2. ALL DIMENSIONS ARE IN MILLIMETERS
NOTES:
1. DIMENSIONING AND TOLERANCING PER ASME Y14.5M-1994
COMPONENT
PIN “A1”
BGA Package
51-Lead (15.00mm × 9.00mm × 4.92mm)
LTM8046
Package Description
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
8046fb
3.810
3.810
LTM8046
Revision History
REV
DATE
DESCRIPTION
PAGE NUMBER
A
07/14
Add MP-grade
2, 3
B
04/15
VIN changed from 32V to 31V
1
8046fb
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 representaFor more
information
www.linear.com/LTM8046
tion that the interconnection
of its circuits
as described
herein will not infringe on existing patent rights.
19
LTM8046
Typical Application
Maximum Output Current vs VIN
12V Isolated Flyback Converter
1µF
3.3V
BIAS
1µF
3.83k
VOUT
12V
VOUT
RUN
FB
SS
MAXIMUM OUTPUT CURRENT (mA)
LTM8046
VIN
ISOLATION BARRIER
VIN
3.3VDC TO 12VDC
300
10µF
×2
VOUT–
GND
2kVAC ISOLATION
250
200
150
100
50
8046 TA04
0
3
6
9
VIN (V)
12
8046 TA04b
Design Resources
SUBJECT
DESCRIPTION
µModule Design and Manufacturing Resources
Design:
• Selector Guides
• Demo Boards and Gerber Files
• Free Simulation Tools
µModule Regulator Products Search
1. Sort table of products by parameters and download the result as a spread sheet.
Manufacturing:
• Quick Start Guide
• PCB Design, Assembly and Manufacturing Guidelines
• Package and Board Level Reliability
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.
Related Parts
PART NUMBER DESCRIPTION
COMMENTS
LTM8057
UL60950 Recognized 1.5W, 2kVAC Isolated µModule 3.1V ≤ VIN ≤ 31V, 2.5V ≤ VOUT ≤ 12V, 5% VOUT Accuracy, Internal Isolated
Transformer, 9mm × 11.25mm × 4.92mm BGA
Converter
LTM8058
UL60950 Recognized 1.5W, 2kVAC Isolated µModule 3.1V ≤ VIN ≤ 31V, 1.2V ≤ VOUT ≤ 12V, 2.5% VOUT Accuracy, 1mVP-P Output
Ripple, Internal Isolated Transformer, 9mm × 11.25mm × 4.92mm BGA
Converter with LDO Post Regulator
LTM8048
1.5W, 725VDC Galvanically Isolated µModule
Converter with LDO Post Regulator
3.1V ≤ VIN ≤ 32V, 1.2V ≤ VOUT ≤ 12V, 2.5% VOUT Accuracy, 1mVP-P Output
Ripple, Internal Isolated Transformer, 9mm × 11.25mm × 4.92mm BGA
LTM8045
Inverting or SEPIC μModule DC/DC Converter with
Up to 700mA Output Current
2.8V ≤ VIN ≤ 18V, ±2.5V ≤ VOUT ≤ ±15V, Synchronizable, No Derating or
Logic Level Shift for Control Inputs When Inverting, 6.25mm × 11.25mm
× 4.92mm BGA
LTM4609
36VIN, 5A DC/DC μModule Buck-Boost Regulator
4.5V ≤ VIN ≤ 36V, 0.8V ≤ VOUT ≤ 34V, Adjustable Soft-Start, Clock Input,
15mm × 15mm × 2.82mm LGA and 15mm × 15mm × 3.42mm BGA
LTM8061
32V, 2A Step-Down μModule Battery Charger with
Programmable Input Current Limit
Suitable for Charging Single and Dual Cell Li-Ion or Li-Poly Batteries, 4.95V ≤ VIN
≤ 32V, C/10 or Adjustable Timer Charge Termination, NTC Resistor Monitor Input,
9mm × 15mm × 4.32mm LGA
8046fb
20 Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
For more information www.linear.com/LTM8046
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com/LTM8046
LT 0415 REV B • PRINTED IN USA
 LINEAR TECHNOLOGY CORPORATION 2014