LTM8021
1
8021fd
For more information www.linear.com/LTM8021
Typical applicaTion
FeaTures
applicaTions
DescripTion
36VIN, 500mA
Step-Down DC/DC
µ
Module
The LT M
®
8021 is a 36VIN 500mA, step-down DC/DC
µModule
®
. 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 L
TM8021 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.
The low profile package (2.82mm) enables utilization of
unused space on the bottom of PC boards for high den-
sity point of load regulation. A built-in soft-start timer is
adjustable with just a resistor and capacitor.
The L
TM8021 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.
7VIN to 36VIN, 5V/500mA µModule Regulator
n Complete Switch Mode Power Supply
n Wide Input Voltage Range: 3V to 36V
n 500mA Output Current
n 0.8V to 5V Output Voltage
n Fixed 1.1MHz Switching Frequency
n Current Mode Control
n (e4) RoHS Compliant Package with Gold
Pad Finish
n Programmable Soft-Start
n Tiny, Low Profile (11.25mm × 6.25mm × 2.82mm)
Surface Mount LGA Package
n Automotive Battery Regulation
n Power for Portable Products
n Distributed Supply Regulation
n Industrial Supplies
n Wall Transformer Regulation
Efficiency and Power Loss
LTM8021
8021 TA01a
VIN*
7V TO
36V
VOUT
5V AT 500mA
1µF 2.2µF
19.1k
RUN/SS
IN
GND ADJ
BIAS
OUT
*RUNNING VOLTAGE RANGE. PLEASE REFER TO THE
APPLICATIONS INFORMATION SECTION FOR START-UP DETAILS. 0
POWER LOSS (mW)
100
200
300
450
400
50
150
250
350
8021 TA01b
LOAD CURRENT (mA)
1.00
30
EFFICIENCY (%)
40
50
70
60
10.00 100.00
90
80
1000.00
POWER
LOSS
EFFICIENCY
L, LT, LTC, LTM, µModule, PolyPhase, Linear Technology and the Linear logo are registered
trademarks of Linear Technology Corporation. All other trademarks are the property of their
respective owners.
LTM8021
2
8021fd
For more information www.linear.com/LTM8021
absoluTe MaxiMuM raTings
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
(Note 1)
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VIN Input DC Voltage VRUN/SS = 5V, RADJ = Open 3 36 V
VOUT Output DC Voltage 0 < IOUT < 500mA; RADJ Open
0 < IOUT < 500mA; RADJ = 19.1k, 0.1%
0.8
5
V
V
RADJ(MIN) Minimum Allowable RADJ Note 3 18 kW
ILK Leakage from IN to OUT RUN/SS = VBIAS = 0V, RADJ Open 2.7 6 µA
IOUT Continuous Output DC Current 5V ≤ VIN ≤ 36V, VBIAS = VOUT 0 500 mA
IQ(VIN) Quiescent Current into VIN RUN/SS = 0.2V, VBIAS, RADJ Open
Not Switching
0.1
1.5
1
2.5
µA
mA
IQ(BIAS) Quiescent Current into BIAS Not Switching 0.15 µA
∆VOUT/VOUT Line Regulation 5V ≤ VIN ≤ 36V, IOUT = 500mA
RADJ = Open
0.5 %
∆VOUT/VOUT Load Regulation VIN = 24V, 0 ≤ IOUT ≤ 500mA, VBIAS = VOUT 0.35 %
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.
orDer inForMaTion
pin conFiguraTion
VIN
BANK 1 VOUT
BANK 2
GND
BANK 3
ADJ
BIAS
RUN/SS
HBA DC
5
1
2
3
4
E F
LGA PACKAGE
35-LEAD (11.25mm × 6.25mm × 2.82mm)
G
TOP VIEW
TJMAX = 125°C, θJA = 36.9°C/W, θJB = 20.9°C/W, WEIGHT = 0.49g
θJC(TOP) = 41.74°C/W, θJC(BOTTOM) = 17.8°C/W
PART NUMBER PAD OR BALL FINISH PART MARKING* PACKAGE
TYPE
MSL
RATING
TEMPERATURE RANGE
(Note 2)
DEVICE FINISH CODE
LTM8021EV#PBF Au (RoHS) LTM8021V e4 LGA 3 –40°C to 125°C
LTM8021IV#PBF Au (RoHS) LTM8021V e4 LGA 3 –40°C to 125°C
Consult Marketing for parts specified with wider operating temperature
ranges. *Device temperature grade is indicated by a label on the shipping
container. Pad or ball finish code is per IPC/JEDEC J-STD-609.
• Terminal Finish Part Marking:
www.linear.com/leadfree
• Recommended LGA and BGA PCB Assembly and Manufacturing
Procedures:
www.linear.com/umodule/pcbassembly
• LGA and BGA Package and Tray Drawings:
www.linear.com/packaging
LTM8021
3
8021fd
For more information www.linear.com/LTM8021
elecTrical characTerisTics
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,
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.
characterization 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.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VOUT(DC) DC Output Voltage VIN = 24V, 0 ≤ IOUT ≤ 500mA
RADJ = 31.6k, 0.1%
3.3
V
VOUT(AC_RMS) Output Voltage Ripple (RMS) VIN = 24V, IOUT = 250mA
COUT = 2.2µF, VBIAS = VOUT
1 mV
fSW Switching Frequency IOUT = 500mA 0.9 1.1 1.3 MHz
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 l0.79 0.80 0.83 V
VBIAS(MIN) Minimum BIAS Voltage for Proper
Operation
IOUT = 500mA 2.2 3 V
IADJ 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 1.6 V
VIL(RUN/SS) RUN/SS Input Low Voltage RADJ Open, IOUT = 500mA 0.5 V
RFB Internal Feedback Resistor RUN/SS = VBIAS = VADJ = 0V 100 kW
LTM8021
4
8021fd
For more information www.linear.com/LTM8021
Typical perForMance characTerisTics
Efficiency vs Load Current
Efficiency vs Load Current
Efficiency vs Load Current
Efficiency vs Load Current
IBIAS vs Load Current
IBIAS vs Load Current
IBIAS vs Load Current
IBIAS vs Load Current
TA = 25°C, unless otherwise noted
LOAD CURRENT (mA)
0
EFFICIENCY (%)
60
85
90
100 200 300
50
75
55
80
45
40
70
65
50 150 400 500
250 350 450
8021 G01
VIN = 36V
VIN = 24V
VIN = 12V
VIN = 5V
VOUT = 1.8V
LOAD CURRENT (mA)
0
EFFICIENCY (%)
60
85
90
100 200 300
50
75
55
80
70
65
50 150 400 500
250 350 450
8021 G02
VIN = 36V
VIN = 24V
VIN = 12V
VIN = 5V
VOUT = 2.5V
LOAD CURRENT (mA)
0
EFFICIENCY (%)
60
85
90
100 200 300
75
55
80
70
65
50 150 400 500
250 350 450
8021 G03
VIN = 36V
VIN = 24V
VIN = 12V
VIN = 5V
VOUT = 3.3V
LOAD CURRENT (mA)
0
EFFICIENCY (%)
60
85
90
100 200 300
75
80
70
65
50 150 400 500
250 350 450
8021 G04
VIN = 36V
VIN = 24V
VIN = 12V
VOUT = 5V
LOAD CURRENT (mA)
0
0
BIAS CURRENT (mA)
2
4
6
100 200 300 400 500
1
3
5
600
8021 G05
VIN = 24V
VIN = 12V
VIN = 5V
VIN = 3.4V
VOUT = 0.8V
LOAD CURRENT (mA)
0
0
BIAS CURRENT (mA)
2
4
6
100 200 300 400 500
8
1
3
5
7
9
600
8021 G06
VIN = 24V
VIN = 12V
VIN = 5V
VIN = 3.4V
VOUT = 1.8V
LOAD CURRENT (mA)
0
0
BIAS CURRENT (mA)
2
4
6
100 200 300 400 500
8
1
3
5
7
600
8021 G07
VIN = 24V
VIN = 12V
VIN = 5V
VOUT = 2.5V
LOAD CURRENT (mA)
0
0
BIAS CURRENT (mA)
2
4
6
100 200 300 400 500
8
10
1
3
5
7
9
600
8021 G08
VIN = 24V
VIN = 12V
VIN = 5V
VOUT = 3.3V
LTM8021
5
8021fd
For more information www.linear.com/LTM8021
Typical perForMance characTerisTics
Input Current vs Output Current Input Current vs Output Current
Input Quiescent Current
vs Input Voltage
Minimum Input Running Voltage
vs Output Voltage
TA = 25°C, unless otherwise noted
Input Current vs Output Current
Output Short-Circuit Current
vs Input Voltage
OUTPUT CURRENT (mA)
0
INPUT CURRENT (mA)
100
350
400
100 200 300
0
250
50
300
200
150
50 150 400 500
250 350 450
8021 G09
VIN = 5V
VOUT = 1.8V
VOUT = 3.3V
VOUT = 2.5V
OUTPUT CURRENT (mA)
0
INPUT CURRENT (mA)
100
300
100 200 300
0
250
50
200
150
50 150 400 500
250 350 450
8021 G10
VIN = 12V
VOUT = 1.8V
VOUT = 5V
VOUT = 3.3V
VOUT = 2.5V
OUTPUT CURRENT (mA)
0
INPUT CURRENT (mA)
40
140
100 200 300
0
100
20
120
80
60
50 150 400 500
250 350 450
8021 G11
VIN = 24V
VOUT = 1.8V
VOUT = 5V
VOUT = 3.3V
VOUT = 2.5V
INPUT VOLTAGE (V)
0
INPUT QUIESCENT CURRENT (µA)
1000
3000
10 20 30
0
2500
500
2000
1500
515 40
25 35
8021 G12
VO = 3.3V
OUTPUT VOLTAGE (V)
0
0
INPUT VOLTAGE (V)
2
4
6
12345
1
3
5
7
6
8021 G13
IOUT = 500mA
INPUT VOLTAGE (V)
4
OUTPUT CURRENT (mA)
840
860
880
32
820
800
12 20
816 24 36
28
740
720
780
900
760
8021 G14
VOUT = 3.3V
Radiated Emissions
FREQUENCY (MHz)
0
EMISSIONS LEVEL (dBµV/m)
50
70
90
800
8021 G15
30
10
40
60
80
20
0
–10 200 400 600 1000
36VIN
5VOUT
FULL LOAD
CISPR22
CLASS B LIMIT
LTM8021
6
8021fd
For more information www.linear.com/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 heat sink 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.
VIN
8021 BD
BIAS
CURRENT MODE
CONTROLLER
VOUT
10µF15pF
10µH
0.1µF
RUN/SS
100k
1%
ADJGND
block DiagraM
LTM8021
7
8021fd
For more information www.linear.com/LTM8021
operaTion
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 feed-
forward 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.
The LTM8021 is a standalone nonisolated 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 perfor-
mance 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.
LTM8021
8
8021fd
For more information www.linear.com/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
LTM8021
9
8021fd
For more information www.linear.com/LTM8021
Capacitor Selection Considerations
The CIN and COUT capacitor values in Table 1 are the
minimum recommended values for the associated oper-
ating conditions. Applying capacitor values below those
indicated in Table 1 is not recommended, and may result
in undesirable operation. Using larger values is generally
acceptable, and can yield improved dynamic response 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.
Ceramic capacitors are small, robust and have very low
ESR. However, not all ceramic capacitors are suitable.
X5R and X7R types are stable over temperature and ap-
plied voltage and give dependable service. Other types,
including Y5V and Z5U have very large temperature and
voltage coefficients of capacitance. In an application cir-
cuit they may have only a small fraction of their nominal
capacitance resulting in much higher output voltage ripple
than expected.
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.
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.
A final precaution regarding ceramic capacitors con-
cerns 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 L
TM8021 circuit is plugged into a live supply, the
input voltage can ring to twice its nominal value, possi-
bly exceeding the device’s rating. This situation is easily
avoided; see the Hot-Plugging Safely section.
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.
applicaTions inForMaTion
Figure 1. The LTM8021 Requires More Voltage to Start Than to Run
LOAD CURRENT (A)
0.001
2.0
INPUT VOLTAGE (V)
3.0
4.0
5.0
0.01 0.1
6.0
2.5
3.5
4.5
5.5
1
8021 F01
VOUT = 3.3V
TO START
TO RUN
LOAD CURRENT (A)
0.001
2
INPUT VOLTAGE (V)
3
4
6
5
0.01 0.1
8
7
1
VOUT = 5V
RUN/SS
ENABLED
RUN/SS
ENABLED
TO START
TO RUN
LTM8021
10
8021fd
For more information www.linear.com/LTM8021
applicaTions inForMaTion
Figure 2. To Soft-Start the LTM8021, Add a
Resistor and Capacitor to the RUN/SS Pin
Soft-Start
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.
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
VOUT
VIN
RUN/SS BIAS
GND
LTM8021
8021 F03
VOUT
RADJ COUT
RT
VIN
4V TO 36V
CIN
CIN
VIN
COUT
FB
GND VOUT
RUN/SS
RADJ
BIAS
PLANE
Figure 4. Layout Showing Suggested External Components,
GND Plane and Thermal Vias
Shorted Input Protection
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.
PCB Layout
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.
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.
8021 F02
RUN/SS
GND
0.22µF
RUN
15k
LTM8021
11
8021fd
For more information www.linear.com/LTM8021
applicaTions inForMaTion
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.
Hot-Plugging Safely
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 volt-
age 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
+
LTM8021
4.7µF
VIN
CLOSING SWITCH
SIMULATES HOT PLUG
IIN
(5a)
(5b)
LOW
IMPEDANCE
ENERGIZED
24V SUPPLY
STRAY
INDUCTANCE
DUE TO 6 FEET
(2 METERS) OF
TWISTED PAIR
+
LTM8021
4.7µF0.1µF
0.7Ω
(5c)
+
LTM8021
4.7µF
22µF
AI.EI.
+
VIN
20V/DIV
IIN
10A/DIV
20µs/DIV
DANGER
RINGING VIN MAY EXCEED
ABSOLUTE MAXIMUM RATING
VIN
20V/DIV
IIN
10A/DIV
20µs/DIV
8021 F05
VIN
20V/DIV
IIN
10A/DIV
20µs/DIV
Figure 5. Ensures Reliable Operation When the LTM8021 is Connected to a Live Supply
LTM8021
12
8021fd
For more information www.linear.com/LTM8021
applicaTions inForMaTion
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 0.7W
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.
Thermal Considerations
The LTM8021 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 Charac-
teristics section can be used as a guide. These curves
were generated by a LTM8021 mounted to a 40.3cm2
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.
The thermal resistance numbers listed in Page 2 of the
data sheet are based on modeling the µModule package
mounted on a test board specified per JESD51-9 (Test
Boards for Area Array Surface Mount Package Thermal
Measurements). The thermal coefficients provided in this
page are based on JESD 51-12 (Guidelines for Reporting
and Using Electronic Package Thermal Information).
For increased accuracy and fidelity to the actual application,
many designers use FEA to predict thermal performance.
To that end, Page 2 of the data sheet typically gives four
thermal coefcients:
θJA – Thermal resistance from junction to ambient.
θJCbottom – Thermal resistance from junction to the bottom
of the product case.
θJCtop – Thermal resistance from junction to top of the
product case.
θJB – Thermal resistance from junction to the printed
circuit board.
While the meaning of each of these coefficients may seem
to be intuitive, JEDEC has defined each to avoid confusion
and inconsistency. These definitions are given in JESD
51-12, and are quoted or paraphrased below:
θJA is the natural convection junction-to-ambient air
thermal resistance measured in a one cubic foot sealed
enclosure. This environment is sometimes referred to as
still air although natural convection causes the air to move.
This value is determined with the part mounted to a JESD
51-9 defined test board, which does not reflect an actual
application or viable operating condition.
θJCbottom is the thermal resistance between the junction
and bottom of the package with all of the component power
dissipation flowing through the bottom of the package. In
the typical µModule converter, the bulk of the heat flows
out the bottom of the package, but there is always heat
flow out into the ambient environment. As a result, this
thermal resistance value may be useful for comparing
packages but the test conditions don’t generally match
the user’s application.
θJCtop is determined with nearly all of the component power
dissipation flowing through the top of the package. As the
electrical connections of the typical µModule converter are
on the bottom of the package, it is rare for an application
to operate such that most of the heat flows from the junc-
tion to the top of the part. As in the case of θJCbottom, this
value may be useful for comparing packages but the test
conditions don’t generally match the user’s application.
LTM8021
13
8021fd
For more information www.linear.com/LTM8021
applicaTions inForMaTion
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.
Given these definitions, it should now be apparent that none
of these thermal coefficients reflects an actual physical
operating condition of a µModule converter. Thus, none
of them can be individually used to accurately predict the
thermal performance of the product. Likewise, it would
be inappropriate to attempt to use any one coefficient to
correlate to the junction temperature 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.
A graphical representation of these thermal resistances
is given in Figure 6.
The blue resistances are contained within the µModule
converter, and the green are outside.
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. The bulk of the heat flow out of the LTM8021
is through the bottom of the μModule converter 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.
8021 F06
µMODULE DEVICE
JUNCTION-TO-CASE (TOP)
RESISTANCE
JUNCTION-TO-BOARD RESISTANCE
JUNCTION-TO-AMBIENT RESISTANCE (JESD 51-9 DEFINED BOARD)
CASE (TOP)-TO-AMBIENT
RESISTANCE
BOARD-TO-AMBIENT
RESISTANCE
JUNCTION-TO-CASE
(BOTTOM) RESISTANCE
JUNCTION AMBIENT
CASE (BOTTOM)-TO-BOARD
RESISTANCE
Figure 6. Thermal Model of µModule Regulator
LTM8021
14
8021fd
For more information www.linear.com/LTM8021
Typical applicaTions
0.8V Step-Down Converter
LTM8021
8021 TA02
VIN*
3.4V TO 36V
5V
VOUT
0.8V AT 500mA
1µF
100µF
RUN/SS
VIN
BIAS
VOUT
GND ADJ
*RUNNING VOLTAGE RANGE. PLEASE REFER TO THE
APPLICATIONS INFORMATION SECTION FOR START-UP DETAILS.
1.8V Step-Down Converter
5V Step-Down Converter
LTM8021
8021 TA04
VIN*
7V TO 36V
VOUT
5V AT 500mA
1µF
*RUNNING VOLTAGE RANGE. PLEASE REFER TO THE
APPLICATIONS INFORMATION SECTION FOR START-UP DETAILS.
2.2µF
19.1k
RUN/SS BIAS
GND ADJ
VIN VOUT
LTM8021
8021 TA03
VIN*
3.4V TO 36V
VOUT
1.8V AT 500mA
1µF
100µF
78.7k
RUN/SS
BIAS
GND ADJ
5V
VIN VOUT
*RUNNING VOLTAGE RANGE. PLEASE REFER TO THE
APPLICATIONS INFORMATION SECTION FOR START-UP DETAILS.
–5V Positive-to-Negative Converter Load Current vs Input Voltage
LTM8021
8021 TA05
VIN*
3.75V TO 31V
1µF
–5V
4.7µF
OPTIONAL
SCHOTTKY
CLAMP
19.1k
RUN/SS BIAS
GND ADJ
VIN VOUT
*RUNNING VOLTAGE RANGE. PLEASE REFER TO THE
APPLICATIONS INFORMATION SECTION FOR START-UP DETAILS.
VIN (V)
0
I
LOAD
(mA)
400
500
300
200
10 20
515 25
100
0
600
8021 TA05b
LTM8021
15
8021fd
For more information www.linear.com/LTM8021
package DescripTion
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
6.250
BSC
PACKAGE TOP VIEW
11.250
BSC
4
PAD 1
CORNER
XY
aaa Z
aaa Z
2.72 – 2.92
DETAIL A
PACKAGE SIDE VIEW
DETAIL A
SUBSTRATE
MOLD
CAP
0.27 – 0.37
2.40 – 2.60
bbb Z
Z
LGA 35 0113 REV B
PACKAGE IN TRAY LOADING ORIENTATION
LTMXXXXXX
µModule
TRAY PIN 1
BEVEL
COMPONENT
PIN “A1”
4.445
4.445
3.175
3.175
1.905
0.0000
1.905
0.635
0.635
1.270
1.270
0.9525
1.5875
0.635
0.9525
0.3175
2.540
2.540
SUGGESTED PCB LAYOUT
TOP VIEW
0.0000
LGA Package
35-Lead (11.25mm × 6.25mm × 2.82mm)
(Reference LTC DWG # 05-08-1805 Rev B)
NOTES:
1. DIMENSIONING AND TOLERANCING PER ASME Y14.5M-1994
2. ALL DIMENSIONS ARE IN MILLIMETERS
LAND DESIGNATION PER JESD MO-222, SPP-010 AND SPP-020
5. PRIMARY DATUM -Z- IS SEATING PLANE
6. THE TOTAL NUMBER OF PADS: 35
4
3
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
SYMBOL
aaa
bbb
TOLERANCE
0.15
0.10
7 PACKAGE ROW AND COLUMN LABELING MAY VARY
AMONG µModule PRODUCTS. REVIEW EACH PACKAGE
LAYOUT CAREFULLY
!
PADS
SEE NOTES
1.270
BSC
0.605 – 0.665
0.605 – 0.665
8.890
BSC
5.080
BSC
PAD 1
C (0.30)
H B AD C
5
1
3
2
3
4
EF
PACKAGE BOTTOM VIEW
G
7
SEE NOTES
LTM8021
16
8021fd
For more information www.linear.com/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
LTM8021
17
8021fd
For more information www.linear.com/LTM8021
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.
REV DATE DESCRIPTION PAGE NUMBER
D 3/14 Updated thermal resistance values
Updated Order Information table
Updated Thermal Considerations section
2
2
12, 13
revision hisTory
(Revision history begins at Rev D)
LTM8021
18
8021fd
For more information www.linear.com/LTM8021
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
LINEAR TECHNOLOGY CORPORATION 2008
LT 0314 REV D • PRINTED IN USA
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LTM8021
relaTeD parTs
package phoTo
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
3.3V Step-Down Converter
Typical applicaTion
LTM8021
8021 TA06
VIN*
5.5V TO 36V
VOUT
3.3V AT 500mA
1µF 4.7µF
32.4k
RUN/SS BIAS
GND ADJ
VIN VOUT
*RUNNING VOLTAGE RANGE. PLEASE REFER TO THE
APPLICATIONS INFORMATION SECTION FOR START-UP DETAILS.