LINER LTM8021V 36vin, 500ma step-down dc/dc î¼module Datasheet

LTM8021
36VIN, 500mA
Step-Down DC/DC µModule
FEATURES
DESCRIPTION
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The LTM®8021 is a 36VIN 500mA, step-down DC/DC
μModuleTM. Included in the package are the switching
controller, power switches, inductor, and all support
components. Operating over an input voltage range of 3V
to 36V, the LTM8021 supports an output voltage range of
0.8V to 5V, set by a single resistor. Only an output and
bulk input capacitor are needed to finish the design.
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Complete Switch Mode Power Supply
Wide Input Voltage Range: 3V to 36V
500mA Output Current
0.8V to 5V Output Voltage
Fixed 1.1MHz Switching Frequency
Current Mode Control
(e4) RoHS Compliant Package with Gold
Pad Finish
Programmable Soft-Start
Tiny, Low Profile (11.25mm × 6.25mm × 2.82mm)
Surface Mount LGA Package
APPLICATIONS
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The low profile package (2.82mm) enables utilization of
unused space on the bottom of PC boards for high density point of load regulation. A built-in soft-start timer is
adjustable with just a resistor and capacitor.
The LTM8021 is packaged in a thermally enhanced,
compact (11.25mm × 6.25mm) and low profile (2.82mm)
overmolded Land Grid Array (LGA) package suitable
for automated assembly by standard surface mount
equipment. The LTM8021 is RoHS compliant.
Automotive Battery Regulation
Power for Portable Products
Distributed Supply Regulation
Industrial Supplies
Wall Transformer Regulation
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
μModule is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
TYPICAL APPLICATION
Efficiency and Power Loss
7VIN to 36VIN, 5V/500mA μModule Regulator
90
LTM8021
RUN/SS
GND
1μF
BIAS
ADJ
19.1k
2.2μF
8021 TA01a
400
80
VOUT
5V AT 500mA
OUT
350
EFFICIENCY
EFFICIENCY (%)
IN
70
300
250
60
200
50
150
POWER
LOSS
40
POWER LOSS (mW)
VIN*
7V TO
36V
450
100
50
*RUNNING VOLTAGE RANGE. PLEASE REFER TO THE
APPLICATIONS INFORMATION SECTION FOR START-UP DETAILS.
30
1.00
10.00
100.00
LOAD CURRENT (mA)
0
1000.00
8021 TA01b
8021fb
1
LTM8021
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
VIN, RUN/SS Voltage .................................................40V
RUN/SS Above VIN ......................................................3V
ADJ Voltage ................................................................5V
BIAS Voltage ...............................................................7V
VOUT Voltage .............................................................10V
Internal Operating Temperature
Range (Note 2) ..................................–40°C to 125°C
Maximum Solder Temperature .............................. 260°C
Storage Temperature Range...................–55°C to 125°C
TOP VIEW
VIN
BANK 1
5
VOUT
BANK 2
4
3
BIAS
ADJ
2
GND
BANK 3
RUN/SS
1
A
B
C
D
E
F
G
H
LGA PACKAGE
35-LEAD (11.25mm s 6.25mm s 2.82mm)
TJMAX = 125°C, θJA = 24.9°C/W, WEIGHT = 0.49g
θJA DERIVED FROM 6.35cm × 6.35cm; 4-LAYER PCB
ORDER INFORMATION
LEAD FREE FINISH
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE (NOTE 2)
LTM8021EV#PBF
LTM8021V
35-Lead (11.25mm × 6.25mm × 2.82mm)
–40°C to 125°C
LTM8021IV#PBF
LTM8021V
35-Lead (11.25mm × 6.25mm × 2.82mm)
–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/
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, RADJ = 31.6k.
SYMBOL
PARAMETER
CONDITIONS
VIN
Input DC Voltage
VRUN/SS = 5V, RADJ = Open
MIN
TYP
VOUT
Output DC Voltage
0 < IOUT < 500mA; RADJ Open
0 < IOUT < 500mA; RADJ = 19.1k, 0.1%
RADJ(MIN)
Minimum Allowable RADJ
Note 3
ILK
Leakage from IN to OUT
RUN/SS = VBIAS = 0V, RADJ Open
IOUT
Continuous Output DC Current
5V ≤ VIN ≤ 36V, VBIAS = VOUT
IQVIN
Quiescent Current into VIN
RUN/SS = 0.2V, VBIAS , RADJ Open
Not Switching
0.1
1.5
IQBIAS
Quiescent Current into BIAS
Not Switching
0.15
μA
ΔVOUT/VOUT
Line Regulation
5V ≤ VIN ≤ 36V, IOUT = 500mA
RADJ = Open
0.5
%
ΔVOUT/VOUT
Load Regulation
VIN = 24V, 0 ≤ IOUT ≤ 500mA, VBIAS = VOUT
0.35
%
3
MAX
36
0.8
5
UNITS
V
V
V
18
kΩ
2.7
0
6
μA
500
mA
1
2.5
μA
mA
8021fb
2
LTM8021
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, RADJ = 31.6k.
SYMBOL
PARAMETER
CONDITIONS
VOUT(DC)
DC Output Voltage
VIN = 24V, 0 ≤ IOUT ≤ 500mA
RADJ = 31.6k, 0.1%
MIN
TYP
MAX
VOUT(AC_RMS)
Output Voltage Ripple (RMS)
VIN = 24V, IOUT = 250mA
COUT = 2.2μF, VBIAS = VOUT
fSW
Switching Frequency
IOUT = 500mA
IOSC
Short-Circuit Output Current
VIN = 36V, VBIAS = VOUT = 0V
900
mA
IISC
Short-Circuit Input Current
VIN = 36V, VBIAS = VOUT = 0V
25
mA
ADJ
Voltage at ADJ Pin
RADJ Open
VBIAS(MIN)
Minimum BIAS Voltage for Proper
Operation
IADJ
3.3
V
1
0.9
l
mV
1.3
MHz
0.80
0.83
V
IOUT = 500mA
2.2
3
V
Current Out of ADJ Pin
VOUT = 5V, VADJ = 0V, RUN/SS = 0V
50
μA
IRUN/SS
RUN/SS Pin Current
VRUN/SS = 2.5V, RADJ Open
23
μA
VIH(RUN/SS)
RUN/SS Input High Voltage
RADJ Open, IOUT = 500mA
VIL(RUN/SS)
RUN/SS Input Low Voltage
RADJ Open, IOUT = 500mA
RFB
Internal Feedback Resistor
RUN/SS = VBIAS = VADJ = 0V
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 LTM8021E 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, characteriza-
0.79
1.1
UNITS
1.6
V
0.5
100
V
kΩ
tion and correlation with statistical process controls. The LTM8021I 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: Guaranteed by design.
8021fb
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LTM8021
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Load Current
VOUT = 1.8V
80
VIN = 5V
75
VIN = 12V
70
VIN = 24V
65
VIN = 36V
60
VOUT = 2.5V
85
EFFICIENCY (%)
85
EFFICIENCY (%)
Efficiency vs Load Current
90
Efficiency vs Load Current
90
VIN = 5V
80
VIN = 12V
75
VIN = 24V
70
VIN = 36V
65
0
0
IBIAS vs Load Current
IBIAS vs Load Current
9
VOUT = 0.8V
VIN = 12V
VOUT = 1.8V
VIN = 3.4V
8
VIN = 3.4V
5
VIN = 24V
75
70
BIAS CURRENT (mA)
7
VIN = 36V
80
50 100 150 200 250 300 350 400 450 500
LOAD CURRENT (mA)
8021 G03
6
BIAS CURRENT (mA)
EFFICIENCY (%)
85
0
8021 G02
Efficiency vs Load Current
VOUT = 5V
70
50 100 150 200 250 300 350 400 450 500
LOAD CURRENT (mA)
8021 G01
90
VIN = 36V
55
50
50 100 150 200 250 300 350 400 450 500
LOAD CURRENT (mA)
75
60
55
40
VIN = 24V
65
60
45
VIN = 5V
VIN = 12V
80
55
50
VOUT = 3.3V
85
EFFICIENCY (%)
90
TA = 25°C, unless otherwise noted
4
VIN = 5V
3
2
VIN = 12V
6
VIN = 5V
5
4
3
VIN = 12V
2
1
65
60
0
0
0
50 100 150 200 250 300 350 400 450 500
LOAD CURRENT (mA)
0
100
300
400
200
LOAD CURRENT (mA)
500
8021 G04
500
600
VOUT = 3.3V
VIN = 5V
8
6
BIAS CURRENT (mA)
BIAS CURRENT (mA)
300
400
200
LOAD CURRENT (mA)
8021 G06
9
VIN = 5V
5
4
VIN = 12V
3
VIN = 24V
2
100
IBIAS vs Load Current
10
VOUT = 2.5V
7
0
600
8021 G05
IBIAS vs Load Current
8
VIN = 24V
1
VIN = 24V
7
6
5
VIN = 12V
4
3
VIN = 24V
2
1
1
0
0
0
100
300
400
200
LOAD CURRENT (mA)
500
600
8021 G07
0
100
300
400
200
LOAD CURRENT (mA)
500
600
8021 G08
8021fb
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LTM8021
TYPICAL PERFORMANCE CHARACTERISTICS
Input Current vs Output Current
VIN = 5V
INPUT CURRENT (mA)
INPUT CURRENT (mA)
250
VOUT = 2.5V
200
150
VOUT = 1.8V
100
200
VOUT = 3.3V
150
VOUT = 2.5V
100
VOUT = 1.8V
50 100 150 200 250 300 350 400 450 500
OUTPUT CURRENT (mA)
0
1000
5
4
3
2
500
1
0
0
10
15 20 25 30
INPUT VOLTAGE (V)
35
40
8021 G12
50 100 150 200 250 300 350 400 450 500
OUTPUT CURRENT (mA)
VOUT = 3.3V
880
OUTPUT CURRENT (mA)
2500
INPUT VOLTAGE (V)
INPUT QUIESCENT CURRENT (μA)
900
IOUT = 500mA
1500
0
Output Short-Circuit Current
vs Input Voltage
7
2000
VOUT = 1.8V
8021 G11
6
5
40
Minimum Input Running Voltage
vs Output Voltage
VO = 3.3V
0
VOUT = 2.5V
60
8021 G10
Input Quiescent Current
vs Input Voltage
3000
VOUT = 3.3V
80
0
50 100 150 200 250 300 350 400 450 500
OUTPUT CURRENT (mA)
8021 G09
100
20
0
0
VOUT = 5V
VOUT = 5V
50
50
VIN = 24V
120
250
300
0
140
VIN = 12V
VOUT = 3.3V
350
Input Current vs Output Current
Input Current vs Output Current
300
INPUT CURRENT (mA)
400
TA = 25°C, unless otherwise noted
860
840
820
800
780
760
740
720
0
1
3
4
2
OUTPUT VOLTAGE (V)
5
6
4
8
12
16
20
24
28
32
36
INPUT VOLTAGE (V)
8021 G13
8021 G14
8021fb
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LTM8021
PIN FUNCTIONS
VIN (Bank 1): The VIN pin supplies current to the LTM8021’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.
VOUT (Bank 2): Power Output Pins. An external capacitor is
connected from VOUT to GND in most applications. Apply
output load between these pins and GND pins.
BIAS (Pin H3): The BIAS pin connects to the internal
boost Schottky diode and to the internal regulator. Tie to
VOUT when VOUT > 3V or to another DC voltage greater
than 3V otherwise. When BIAS > 3V the internal circuitry
will be powered from this pin to improve efficiency. Main
regulator power will still come from VIN.
RUN/SS (Pin A1): Tie RUN/SS pin to ground to shut down
the LTM8021. Tie to 1.6V or more for normal operation.
If the shutdown feature is not used, tie this pin to the VIN
pin. The RUN/SS also provides soft-start and frequency
foldback. To use the soft-start function, connect a resistor and capacitor to this pin. Do not allow the RUN/SS
pin to rise above VIN. See the Applications Information
section.
GND (Bank 3): The GND connections serve as the main
signal return and the primary heatsink for the LTM8021. Tie
the GND pins to a local ground plane below the LTM8021
and the circuit components. Return the feedback divider
to this signal.
ADJ (Pin A2): The LTM8021 regulates its ADJ pin
to 0.8V. Connect the adjust resistor from this pin to
ground. The value of RADJ is given by the equation,
RADJ = 80/(VOUT – 0.8), where RADJ is in k.
BLOCK DIAGRAM
VIN
VOUT
10μH
0.1μF
15pF
100k
1%
10μF
BIAS
RUN/SS
CURRENT MODE
CONTROLLER
GND
ADJ
8021 BD
8021fb
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LTM8021
OPERATION
The LTM8021 is a stand alone non-isolated step down
switching DC/DC power supply. It can deliver up to
500mA 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 5VDC . The input voltage range is 3V
to 36V. Given that the LTM8021 is a step down converter,
make sure that the input voltage is high enough to support
the desired output voltage and load current. Please refer
to the simplified Block Diagram.
The LTM8021 contains a current mode controller, power
switching element, power inductor, power Schottky diode
and a modest amount of input and output capacitance.
With its high performance current mode controller and
internal feedback loop compensation, the LTM8021 module
has sufficient stability margin and good transient performance under a wide range of operating conditions with a
wide range of output capacitors, even all ceramic ones (X5R
or X7R). Current mode control provides cycle-by-cycle fast
current limit, and automatic current limiting protects the
module in the event of a short-circuit or overload fault.
The LTM8021 is based upon a 1.1MHz fixed frequency
PWM current mode controller, equipped with cycle skip
capability for low voltage outputs or light loads. A frequency foldback scheme helps to protect internal components from overstress under heavy and short-circuit
output loads.
The drive circuit for the internal power switching element
is powered through the BIAS pin. Power this pin with at
least 3V.
APPLICATIONS INFORMATION
For most applications, the design process is straight
forward, summarized as follows:
1. Refer to Table 1 for the row that has the desired input
range and output voltage.
2. Apply the recommended CIN, COUT, and RADJ values.
3. Connect BIAS as indicated.
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.
If the desired output voltage is not listed in Table 1, set the
output by applying an RADJ resistor whose value is given
by the equation, RADJ = 80/(VOUT – 0.80), where RADJ is
in k and VOUT is in volts. Verify the LTM8021’s operation
over the system’s intended line, load and environmental
conditions.
Minimum Duty Cycle
The LTM8021 has a fixed 1.1MHz switching frequency. For
any given output voltage, the duty cycle falls as the input
voltage rises. At very large VIN to VOUT ratios, the duty
cycle can be very small. Because the LTM8021’s internal
controller IC has a minimum on-time, the regulator will
skip cycles in order to maintain output voltage regulation.
This will result in a larger output voltage ripple and possible disturbances during recovery from a transient load
step. The component values provided in Table 1 allow for
skip cycle operation, but hold the resultant output ripple
to around 50mV, or less. If even less ripple is desired,
then more output capacitance may be necessary. Adding
a feedforward capacitor has been empirically shown to
modestly extend the input voltage range to where the
LTM8021 does not skip cycles. Apply the feedforward
capacitor between the VOUT pins and ADJ. This injects
perturbations into the control loop, therefore, values
larger than 50pF are not recommended. A good value to
start with is 12pF.
8021fb
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LTM8021
APPLICATIONS INFORMATION
Table 1. Recommended Component Values and Configuration
VIN RANGE
VOUT
CIN
COUT
RADJ
BIAS
3.4V to 36V
0.8V
4.7μF
100μF 1210
8.2M
3V to 7V
3.4V to 36V
1.2V
4.7μF
100μF 1210
200k
3V to 7V
3.4V to 36V
1.5V
4.7μF
100μF 1210
115k
3V to 7V
3.4V to 36V
1.8V
2.2μF
100μF 1210
78.7k
3V to 7V
3.5V to 36V
2V
2.2μF
100μF 1210
66.5k
3V to 7V
4V to 36V
2.2V
1μF
22μF 1206
57.6k
3V to 7V
4V to 36V
2.5V
1μF
10μF 0805
47.5k
3V to 7V
5V to 36V
3.3V
1μF
4.7μF 0805
32.4k
VOUT
7V to 36V
5V
1μF
2.2μF 0805
19.1k
VOUT
3.5V to 32V
–3.3V
1μF
4.7μF 0805
32.4k
GND
3.75V to 31V
–5V
1μF
4.7μF 0805
19.1k
GND
3.4V to 15V
0.8V
4.7μF
100μF 1210
8.2M
3V to 7V
3.4V to 15V
1.2V
4.7μF
100μF 1210
200k
3V to 7V
3.4V to 15V
1.5V
4.7μF
47μF 1206
115k
3V to 7V
3.4V to 15V
1.8V
2.2μF
47μF 1206
78.7k
3V to 7V
3.5V to 15V
2V
2.2μF
22μF 1206
66.5k
3V to 7V
4V to 15V
2.2V
1μF
22μF 1206
57.6k
3V to 7V
4V to 15V
2.5V
1μF
10μF 0805
47.5k
3V to 7V
5V to 15V
3.3V
1μF
2.2μF 0805
32.4k
VOUT
7V to 15V
5V
1μF
1μF 0805
19.1k
VOUT
9V to 24V
0.8V
1μF
100μF 1210
Open
3V to 7V
9V to 24V
1.2V
1μF
100μF 1210
200k
3V to 7V
9V to 24V
1.5V
1μF
47μF 1206
115k
3V to 7V
9V to 24V
1.8V
1μF
47μF 1206
78.7k
3V to 7V
9V to 24V
2V
1μF
22μF 1206
66.5k
3V to 7V
9V to 24V
2.2V
1μF
22μF 1206
57.6k
3V to 7V
9V to 24V
2.5V
1μF
10μF 0805
47.5k
3V to 7V
9V to 24V
3.3V
1μF
2.2μF 0805
32.4k
VOUT
9V to 24V
5V
1μF
1μF 0805
19.1k
VOUT
18V to 36V
0.8V
1uF
100μF 1210
Open
3V to 7V
18V to 36V
1.2V
1uF
100μF 1210
200k
3V to 7V
18V to 36V
1.5V
1uF
100μF 1210
115k
3V to 7V
18V to 36V
1.8V
1uF
100μF 1210
78.7k
3V to 7V
18V to 36V
2V
1uF
100μF 1210
66.5k
3V to 7V
18V to 36V
2.2V
1uF
22μF 1206
57.6k
3V to 7V
18V to 36V
2.5V
1uF
10μF 0805
47.5k
3V to 7V
18V to 36V
3.3V
1uF
4.7μF 0805
32.4k
VOUT
18V to 36V
5V
1uF
2.2μF 0805
19.1k
VOUT
8021fb
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LTM8021
APPLICATIONS INFORMATION
If this audible noise is unacceptable, use a high performance
electrolytic capacitor at the output. This output capacitor
can be a parallel combination of a 1μF ceramic capacitor
and a low cost electrolytic capacitor.
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 or
fault recovery, 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.
A final precaution regarding ceramic capacitors concerns the maximum input voltage rating of the LTM8021.
A ceramic input capacitor combined with trace or cable
inductance forms a high Q (under damped) tank circuit.
If the LTM8021 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.
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.
Minimum Input Voltage
The LTM8021 is a step-down converter, so a minimum
amount of headroom is required to keep the output in
regulation. For most applications at full load, the input
must be about 1.5V above the desired output. In addition,
it takes more input voltage to turn on than is required for
continuous operation. This is shown in Figure 1.
Ceramic capacitors are also piezoelectric. At light loads,
the LTM8021 skips switching cycles in order to maintain
regulation. The resulting bursts of current can excite
a ceramic capacitor at audio frequencies, generating
audible noise.
8
6.0
VOUT = 5V
VOUT = 3.3V
5.5
7
TO START
TO START
6
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
5.0
RUN/SS
ENABLED
5
TO RUN
4
4.5
4.0
RUN/SS
ENABLED
3.5
TO RUN
3.0
3
2
0.001
2.5
0.01
0.1
LOAD CURRENT (A)
1
2.0
0.001
0.01
0.1
LOAD CURRENT (A)
1
8021 F01
Figure 1. The LTM8021 Requires More Voltage to Start Than to Run
8021fb
9
LTM8021
APPLICATIONS INFORMATION
Soft-Start
Shorted Input Protection
The RUN/SS pin can be used to soft-start the LTM8021,
reducing the maximum input current during start-up.
The RUN/SS pin is driven through an external RC filter
to create a voltage ramp at this pin. Figure 2 shows the
soft-start circuit. By choosing a large 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 80μA
when the RUN/SS pin reaches 2V.
Care needs to be taken in systems where the output will
be held high when the input to the LTM8021 is absent.
This may occur in battery charging applications or in
battery backup systems where a battery or some other
supply is diode ORed with the LTM8021’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 LTM8021’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
the RUN/SS pin is grounded, the internal power 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 LTM8021 can pull large currents from
the output through the internal power switch and the VIN
pin. Figure 3 shows a circuit that will run only when the
input voltage is present and that protects against a shorted
or reversed input.
RUN
15k
RUN/SS
0.22μF
GND
8021 F02
Figure 2. To Soft-Start the LTM8021, Add a
Resisitor and Capacitor to the RUN/SS Pin
LTM8021
VIN
4V TO 36V
VIN
VOUT
RUN/SS
BIAS
GND
CIN
VOUT
RT
COUT
RADJ
8021 F03
Figure 3. The Input Diode Prevents a Shorted Input from
Discharging a Backup Battery Tied to the Output. It Also Protects
the Circuit from a Reversed Input. The LTM8021 Runs Only When
the Input is Present
8021fb
10
LTM8021
APPLICATIONS INFORMATION
PCB Layout
Hot-Plugging Safely
Most of the problems associated with the PCB layout
have been alleviated or eliminated by the high level of
integration of the LTM8021. The LTM8021 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, one may fail to achieve a specified
operation with a haphazard or poor layout. See Figure 4
for a suggested layout.
The small size, robustness and low impedance of ceramic
capacitors make them an attractive option for the input
bypass capacitor of LTM8021. However, these capacitors
can cause problems if the LTM8021 is plugged into a live
supply (see the 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 LTM8021 can ring to twice the
nominal input voltage, possibly exceeding the LTM8021’s
rating and damaging the part. If the input supply is poorly
controlled or the user will be plugging the LTM8021 into
an energized supply, the input network should be designed
to prevent this overshoot. Figure 5 shows the waveforms
that result when an LTM8021 circuit is connected to a 24V
supply through six feet of 24-gauge twisted pair. The first
plot 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. In Figure 5b an aluminum electrolytic capacitor
has been added. 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. An alternative solution is shown in Figure
5c. 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. This solution is smaller and less expensive than
the electrolytic capacitor. 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.
Ensure that the grounding and heatsinking are acceptable.
A few rules to keep in mind are:
1. Place the CIN capacitor as close as possible to the VIN
and GND connection of the LTM8021.
2. Place the COUT capacitor as close as possible to the
VOUT and GND connection of the LTM8021.
3. Place the CIN and COUT capacitors such that their ground
currents flow directly adjacent to, or underneath, the
LTM8021.
4. 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 LTM8021.
VIN
PLANE VOUT
COUT
BIAS
CIN
GND
RADJ
FB
RUN/SS
8021 F04
Figure 4. Layout Showing Suggested External Components,
GND Plane and Thermal Vias
8021fb
11
LTM8021
APPLICATIONS INFORMATION
CLOSING SWITCH
SIMULATES HOT PLUG
IIN
VIN
DANGER
VIN
20V/DIV
RINGING VIN MAY EXCEED
ABSOLUTE MAXIMUM RATING
LTM8021
+
4.7μF
LOW
IMPEDANCE
ENERGIZED
24V SUPPLY
IIN
10A/DIV
STRAY
INDUCTANCE
DUE TO 6 FEET
(2 METERS) OF
TWISTED PAIR
20μs/DIV
(5a)
LTM8021
+
+
22μF
AI.EI.
VIN
20V/DIV
4.7μF
IIN
10A/DIV
(5b)
0.7Ω
LTM8021
20μs/DIV
VIN
20V/DIV
+
0.1μF
4.7μF
IIN
10A/DIV
(5c)
20μs/DIV
8021 F05
Figure 5. Ensures Reliable Operation When the LTM8021 is Connected to a Live Supply
High Temperature Considerations
The die temperature of the LTM8021 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 LTM8021. To estimate the junction temperature, approximate the power dissipation within the LTM8021 by
applying the typical efficiency stated in this datasheet to
the desired output power, or, if one has an actual module,
by taking a power measurement. Then, calculate the temperature rise of the LTM8021 junction above the surface
of the printed circuit board by multiplying the module’s
power dissipation by the thermal resistance. The actual
thermal resistance of the LTM8021 to the printed circuit
board depends on the layout of the circuit board, but the
thermal resistance given on page 2, which is based upon
a 40.3cm2 4-layer FR4 PC board, can be used a guide.
Finally, be aware that at high ambient temperatures the
internal Schottky diode will have significant leakage current
(see the Typical Performance Characteristics) increasing
the quiescent current of the LTM8021.
8021fb
12
LTM8021
TYPICAL APPLICATIONS
1.8V Step-Down Converter
0.8V Step-Down Converter
LTM8021
VIN*
3.4V TO 36V
VIN
5V
VIN
5V
BIAS
RUN/SS
1μF
LTM8021
VIN*
3.4V TO 36V
VOUT
0.8V AT 500mA
VOUT
GND
VOUT
1.8V AT 500mA
VOUT
BIAS
RUN/SS
100μF
GND
ADJ
100μF
ADJ
1μF
78.7k
8021 TA02
8021 TA03
*RUNNING VOLTAGE RANGE. PLEASE REFER TO THE
APPLICATIONS INFORMATION SECTION FOR START-UP DETAILS.
*RUNNING VOLTAGE RANGE. PLEASE REFER TO THE
APPLICATIONS INFORMATION SECTION FOR START-UP DETAILS.
5V Step-Down Converter
LTM8021
VIN*
7V TO 36V
VIN
VOUT
RUN/SS
BIAS
GND
1μF
VOUT
5V AT 500mA
ADJ
2.2μF
19.1k
8021 TA04
*RUNNING VOLTAGE RANGE. PLEASE REFER TO THE
APPLICATIONS INFORMATION SECTION FOR START-UP DETAILS.
–5V Positive-to-Negative Converter
Load Current vs Input Voltage
600
LTM8021
VIN
VOUT
RUN/SS
BIAS
500
400
4.7μF
GND
1μF
ADJ
OPTIONAL
SCHOTTKY
CLAMP
300
200
19.1k
–5V
8021 TA05
*RUNNING VOLTAGE RANGE. PLEASE REFER TO THE
APPLICATIONS INFORMATION SECTION FOR START-UP DETAILS.
ILOAD (mA)
VIN*
3.75V TO 31V
100
0
0
5
10
15
20
25
VIN (V)
8021 TA05b
8021fb
13
LTM8021
PACKAGE DESCRIPTION
LGA Package
35-Lead (11.25mm × 6.25mm × 2.82mm)
(Reference LTC DWG # 05-08-1805 Rev A)
11.250
BSC
aaa Z
X
2.72 – 2.92
Y
MOLD
CAP
6.250
BSC
SUBSTRATE
0.27 – 0.37
PAD 1
CORNER
Z
bbb Z
2.40 – 2.60
DETAIL A
aaa Z
PACKAGE TOP VIEW
4
4.445
3.175
1.905
0.635
0.0000
0.635
1.905
3.175
4.445
DETAIL A
PACKAGE SIDE VIEW
8.890
BSC
0.605 – 0.665
PADS
SEE NOTES
3
5
2.540
1.270
4
0.605 – 0.665
5.080
BSC
0.0000
0.9525
1.270
1.5875
3
2
1.270
BSC
1
0.9525
0.635
0.3175
2.540
H
G
F
E
D
C
B
A
PAD 1
C (0.30)
PACKAGE BOTTOM VIEW
SUGGESTED PCB LAYOUT
TOP VIEW
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 A
MARKED FEATURE
LTMXXXXXX
MModule
5. PRIMARY DATUM -Z- IS SEATING PLANE
6. THE TOTAL NUMBER OF PADS: 35
COMPONENT
PIN “A1”
8021fb
14
LTM8021
PACKAGE DESCRIPTION
LTM8021 Pinout (Sorted by Pin Number)
PIN
SIGNAL DESCRIPTION
A1
RUN/SS
A2
ADJ
A4
VIN
A5
VIN
B1
GND
B2
GND
B4
VIN
B5
VIN
C1
GND
C2
GND
D1
GND
D2
GND
D3
GND
D4
GND
D5
GND
E1
GND
E2
GND
E3
GND
E4
GND
E5
GND
F1
GND
F2
GND
F3
VOUT
F4
VOUT
F5
VOUT
G1
GND
G2
GND
G3
VOUT
G4
VOUT
G5
VOUT
H1
GND
H2
GND
H3
BIAS
H4
VOUT
H5
VOUT
8021fb
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.
15
LTM8021
TYPICAL APPLICATION
3.3V Step-Down Converter
LTM8021
VIN*
5.5V TO 36V
VIN
VOUT
RUN/SS
BIAS
GND
1μF
VOUT
3.3V AT 500mA
ADJ
32.4k
4.7μF
8021 TA06
*RUNNING VOLTAGE RANGE. PLEASE REFER TO THE
APPLICATIONS INFORMATION SECTION FOR START-UP DETAILS.
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTM4600
10A DC/DC μModule
Basic 10A DC/DC μModule, 15mm × 15mm × 2.8mm LGA
LTM4600HVMPV
Military Plastic 10A DC/DC μModule
–55°C to 125°C Operation, 15mm × 15mm × 2.8mm LGA
LTM4601/
LTM4601A
12A DC/DC μModule with PLL, Output Tracking/Margining
and Remote Sensing
Synchronizable, PolyPhase® Operation, LTM4601-1 Version Has No
Remote Sensing
LTM4602
6A DC/DC μModule
Pin-Compatible with the LTM4600
LTM4603
6A DC/DC μModule with PLL and Output Tracking/
Margining and Remote Sensing
Synchronizable, PolyPhase Operation, LTM4603-1 Version Has No
Remote Sensing, Pin-Compatible with the LTM4601
LTM4604
4A Low VIN DC/DC μModule
2.375V ≤ VIN ≤ 5V, 0.8V ≤ VOUT ≤ 5V, 9mm × 15mm × 2.3mm LGA
LTM4605
5A to 12A Buck-Boost μModule
High Efficiency, Adjustable Frequency, 4.5V ≤ VIN ≤ 20V, 0.8V ≤ VOUT ≤
16V, 15mm × 15mm × 2.8mm
LTM4607
5A to 12A Buck-Boost μModule
High Efficiency, Adjustable Frequency, 4.5V ≤ VIN ≤ 36V, 0.8V ≤ VOUT ≤
25V, 15mm × 15mm × 2.8mm
LTM4608
8A Low VIN DC/DC μModule
2.375V ≤ VIN ≤ 5V, 0.8V ≤ VOUT ≤ 5V, 9mm × 15mm × 2.8mm LGA
LTM8020
36V, 200mA DC/DC μModule
4V ≤ VIN ≤ 36V, 1.25V ≤ VOUT ≤ 5V, 6.25mm × 6.25mm × 2.3mm LGA
LTM8022
1A, 36V DC/DC μModule
Adjustable Frequency, 0.8V ≤ VOUT ≤ 5V, 11.25mm × 9mm × 2.82mm,
Pin-Compatible to the LTM8023
LTM8023
2A, 36V DC/DC μModule
Adjustable Frequency, 0.8V ≤ VOUT ≤ 5V, 11.25mm × 9mm × 2.82mm,
Pin-Compatible to the LTM8022
PolyPhase is a trademark of Linear Technology Corporation
8021fb
16 Linear Technology Corporation
LT 1208 REV B • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2008
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