Linear Technology LTM8021 User Manual

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Page 1

LTM8021

EFFICIENCY (%)

36VIN, 500mA

FeaTures

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

Automotive Battery Regulation

Power for Portable Products

Distributed Supply Regulation

Industrial Supplies

Wall Transformer Regulation

Step-Down DC/DC

Module

DescripTion

The LTM®8021 is a 36VIN 500mA, step-down DC/DC

µModule controller, power switches, inductor, and all support components. Operating over an input voltage range of 3V to 36V, the L

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 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.

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.

. Included in the package are the switching

TM8021 supports an output voltage range of

TM8021 is packaged in a thermally enhanced,

Typical applicaTion

7VIN to 36VIN, 5V/500mA µModule Regulator

VIN*

7V TO

36V

*RUNNING VOLTAGE RANGE. PLEASE REFER TO THE APPLICATIONS INFORMATION SECTION FOR START-UP DETAILS.

RUN/SS

1µF

LTM8021

OUT

BIAS

GND ADJ

19.1k

8021 TA01a

OUT

5V AT 500mA

2.2µF

Efﬁciency and Power Loss

EFFICIENCY

1.00

10.00 100.00

LOAD CURRENT (mA)

POWER LOSS

1000.00

8021 TA01b

450

400

350

POWER LOSS (mW)

300

250

200

150

100

8021fd

For more information www.linear.com/LTM8021

Page 2

LTM8021

TOP VIEW

absoluTe MaxiMuM raTings

pin conFiguraTion

(Note 1)

VIN, RUN/SS Voltage ................................................. 40V

RUN/SS Above V

ADJ Voltage ................................................................5V

BIAS Voltage ...............................................................7V

Voltage ............................................................. 10V

OUT

Internal Operating Temperature

Range (Note 2) .......................................–40°C to 125°C

Maximum Solder Temperature .............................. 260°C

Storage Temperature Range .................. – 55°C to 125°C

......................................................3V

BANK 1

ADJ

RUN/SS

E F

35-LEAD (11.25mm × 6.25mm × 2.82mm)

= 125°C, θJA = 36.9°C/W, θJB = 20.9°C/W, WEIGHT = 0.49g

JMAX

JC(TOP)

LGA PACKAGE

= 41.74°C/W, θ

JC(BOTTOM)

= 17.8°C/W

HBA DC

orDer inForMaTion

PART NUMBER PAD OR BALL FINISH PART MARKING* PACKAGE

DEVICE

FINISH CODE

TYPE

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

MSL

RATING

TEMPERATURE RANGE (Note 2)

OUT

BANK 2

BIAS

GND BANK 3

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

The l denotes the speciﬁcations which apply over the full operating

elecTrical characTerisTics

temperature range, otherwise speciﬁcations are at TA = 25°C, VIN = 10V, V

• Recommended LGA and BGA PCB Assembly and Manufacturing

Procedures:

www.linear.com/umodule/pcbassembly

• LGA and BGA Package and Tray Drawings:

.linear.com/packaging

www

RUN/SS

= 10V, V

BIAS

= 3V, R

= 31.6k.

ADJ

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

OUT

ADJ(MIN)

OUT

Q(VIN)

Q(BIAS)

∆V

OUT/VOUT

∆V

OUT/VOUT

Input DC Voltage V

Output DC Voltage 0 < I

Minimum Allowable R

ADJ

Leakage from IN to OUT RUN/SS = V

Continuous Output DC Current 5V ≤ VIN ≤ 36V, V

Quiescent Current into V

Quiescent Current into BIAS Not Switching 0.15 µA

Line Regulation 5V ≤ VIN ≤ 36V, I

Load Regulation VIN = 24V, 0 ≤ I

= 5V, R

RUN/SS

< 500mA; R

OUT

0 < I

< 500mA; R

OUT

Note 3

BIAS

RUN/SS = 0.2V, V Not Switching

= Open

ADJ

OUT

= Open 3 36 V

ADJ

Open

ADJ

= 19.1k, 0.1%

ADJ

= 0V, R

ADJ

= V

BIAS

, R

BIAS

= 500mA

OUT

≤ 500mA, V

Open 2.7 6 µA

OUT

Open

ADJ

= V

BIAS

OUT

0.8 5

0 500 mA

0.1

1.5

0.5 %

0.35 %

2.5

µA

V V

8021fd

For more information www.linear.com/LTM8021

Page 3

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, V

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

OUT(DC)

OUT(AC_RMS)

OSC

ISC

DC Output Voltage

Output Voltage Ripple (RMS) VIN = 24V, I

Switching Frequency I

Short-Circuit Output Current VIN = 36V, V

Short-Circuit Input Current VIN = 36V, V

ADJ Voltage at ADJ Pin R

BIAS(MIN)

Minimum BIAS Voltage for Proper

VIN = 24V, 0 ≤ I R

= 31.6k, 0.1%

ADJ

= 2.2µF, V

OUT

= 500mA 0.9 1.1 1.3 MHz

OUT

Open

ADJ

= 500mA 2.2 3 V

OUT

Operation

ADJ

RUN/SS

IH(RUN/SS)

IL(RUN/SS)

Current Out of ADJ Pin V

RUN/SS Pin Current V

RUN/SS Input High Voltage R

RUN/SS Input Low Voltage R

Internal Feedback Resistor RUN/SS = V

= 5V, V

OUT

RUN/SS

Open, I

ADJ

Open, I

ADJ

= 2.5V, R

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,

≤ 500mA

OUT

= 250mA

OUT

= V

BIAS

= V

BIAS

OUT

= V

BIAS

OUT

= 0V, RUN/SS = 0V 50 µA

ADJ

Open 23 µA

ADJ

= 500mA 1.6 V

OUT

= 500mA 0.5 V

OUT

= V

BIAS

ADJ

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.

RUN/SS

= 10V, V

BIAS

= 3V, R

= 31.6k.

ADJ

3.3

1 mV

OUT

= 0V 900 mA

= 0V 25 mA

0.79 0.80 0.83 V

= 0V 100

For more information www.linear.com/LTM8021

8021fd

Page 4

LTM8021

EFFICIENCY (%)

BIAS CURRENT (mA)

Typical perForMance characTerisTics

Efﬁciency vs Load Current

= 1.8V

OUT

100

VIN = 5V

VIN = 12V

VIN = 24V

VIN = 36V

200

150 LOAD CURRENT (mA)

Efﬁciency vs Load Current

= 5V

OUT

EFFICIENCY (%)

VIN = 12V

VIN = 24V

VIN = 36V

200

150

100

LOAD CURRENT (mA)

250

300

350

400

450

8021 G01

450

8021 G04

500

Efﬁciency vs Load Current

= 2.5V

OUT

100

VIN = 5V

VIN = 12V

VIN = 24V

VIN = 36V

200

150

250

LOAD CURRENT (mA)

vs Load Current

BIAS

= 0.8V

OUT

BIAS CURRENT (mA)

100

300 400 500

200

LOAD CURRENT (mA)

300

350

VIN = 3.4V

VIN = 5V

VIN = 12V

VIN = 24V

= 25°C, unless otherwise noted

Efﬁciency vs Load Current

OUT

400

450

8021 G02

500

BIAS

OUT

600

8021 G05

= 3.3V

100

VIN = 5V

VIN = 12V

VIN = 24V

VIN = 36V

200

150

250

LOAD CURRENT (mA)

vs Load Current

= 1.8V

100

200

LOAD CURRENT (mA)

VIN = 3.4V

300 400 500

300

350

VIN = 5V

VIN = 12V

VIN = 24V

400

450

8021 G03

8021 G06

500

600

vs Load Current

BIAS

= 2.5V

OUT

BIAS CURRENT (mA)

100

VIN = 5V

VIN = 12V

VIN = 24V

300 400 500

200

LOAD CURRENT (mA)

BIAS

OUT

600

8021 G07

For more information www.linear.com/LTM8021

vs Load Current

= 3.3V

100

300 400 500

200

LOAD CURRENT (mA)

VIN = 5V

VIN = 12V

VIN = 24V

600

8021 G08

8021fd

Page 5

LTM8021

INPUT CURRENT (mA)

400

INPUT CURRENT (mA)

140

INPUT VOLTAGE (V)

OUTPUT CURRENT (mA)

900

Typical perForMance characTerisTics

Input Current vs Output Current

350

300

250

200

150

100

VIN = 5V

= 2.5V

OUT

200

150

100

OUTPUT CURRENT (mA)

250

300

350

Input Quiescent Current vs Input Voltage

3000

VO = 3.3V

2500

2000

1500

1000

500

INPUT QUIESCENT CURRENT (µA)

OUT

= 3.3V

OUT

400

= 1.8V

450

8021 G09

500

Input Current vs Output Current

300

VIN = 12V

250

200

150

100

OUTPUT CURRENT (mA)

150

OUT

= 2.5V

200

250

= 3.3V

OUT

300

350

OUT

TA = 25°C, unless otherwise noted

Input Current vs Output Current

VIN = 24V

120

100

OUTPUT CURRENT (mA)

OUT

= 1.8V

400

= 5V

450

8021 G10

500

Minimum Input Running Voltage vs Output Voltage

= 500mA

OUT

150

OUT

= 2.5V

200

250

OUT

= 3.3V

300

350

= 5V

OUT

= 1.8V

OUT

500

450

400

8021 G11

INPUT VOLTAGE (V)

Output Short-Circuit Current vs Input Voltage

= 3.3V

OUT

880

860

840

820

800

780

760

740

720

12 20

16 243628

INPUT VOLTAGE (V)

8021 G12

8021 G14

For more information www.linear.com/LTM8021

OUTPUT VOLTAGE (V)

Radiated Emissions

36V

OUT

FULL LOAD

EMISSIONS LEVEL (dBµV/m)

–10

200

400

FREQUENCY (MHz)

3 4 5

CISPR22

CLASS B LIMIT

600

800

8021 G13

1000

8021 G15

8021fd

Page 6

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.

(Bank 2): Power Output Pins. An external capacitor is

OUT

connected from V

to GND in most applications. Apply

OUT

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 V

OUT

when V

> 3V or to another DC voltage greater

OUT

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.

block DiagraM

If the shutdown feature is not used, tie this pin to the V

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 V

. 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 R (V

– 0.8), where R

OUT

is given by the equation, R

ADJ

is in k.

ADJ

= 80/

RUN/SS

0.1µF

CURRENT MODE

CONTROLLER

10µH

OUT

100k 1%

ADJGND

10µF15pF

BIAS

8021 BD

8021fd

For more information www.linear.com/LTM8021

Page 7

operaTion

LTM8021

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 0.8V

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

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.

, C

2. Apply the recommended C

OUT

and R

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 R by the equation, R in k and V

OUT

ADJ

is in volts. Verify the LTM8021’s operation

resistor whose value is given

ADJ

= 80/(V

– 0.80), where R

OUT

over the system’s intended line, load and environmental conditions.

ADJ

values.

ADJ

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 cir

cuit 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.

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 V

to V

ratios, the duty

OUT

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 V

pins and ADJ. This injects perturbations into the

OUT

control loop, therefore, values larger than 50pF are not recommended. A good value to start with is 12pF.

For more information www.linear.com/LTM8021

8021fd

Page 8

LTM8021

applicaTions inForMaTion

Table 1. Recommended Component Values and Conﬁguration

VIN RANGE V

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 V

7V to 36V 5V 1µF 2.2µF 0805 19.1k V

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 V

7V to 15V 5V 1µF 1µF 0805 19.1k V

OUT

ADJ

BIAS

OUT

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 V

9V to 24V 5V 1µF 1µF 0805 19.1k V

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 V

18V to 36V 5V 1uF 2.2µF 0805 19.1k V

OUT

8021fd

For more information www.linear.com/LTM8021

Page 9

applicaTions inForMaTion

LTM8021

Capacitor Selection Considerations

The CIN and C

capacitor values in Table 1 are the

OUT

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.

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.

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 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 L

TM8021 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.

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.

6.0 V

0.001

= 3.3V

OUT

RUN/SS

ENABLED

TO START

TO RUN

0.01 0.1 LOAD CURRENT (A)

8021 F01

= 5V

OUT

RUN/SS

ENABLED

INPUT VOLTAGE (V)

0.001

TO START

TO RUN

0.01 0.1

LOAD CURRENT (A)

5.5

5.0

4.5

4.0

3.5

INPUT VOLTAGE (V)

3.0

2.5

2.0

Figure 1. The LTM8021 Requires More Voltage to Start Than to Run

8021fd

For more information www.linear.com/LTM8021

Page 10

LTM8021

8021 F04

RUN

applicaTions inForMaTion

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.

15k

0.22µF

RUN/SS

GND

8021 F02

Figure 2. To Soft-Start the LTM8021, Add a Resistor and Capacitor to the RUN/SS Pin

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

pin is allowed to ﬂoat and the RUN/SS pin is held high

(either by a logic signal or because it is tied to V

), 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 V

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 V

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:

Place the C

capacitor as close as possible to the VIN

and GND connection of the LTM8021.

Place the C

and GND connection of the LTM8021.

OUT

3. Place the C

capacitor as close as possible to the

OUT

and C

capacitors such that their ground

OUT

currents ﬂow directly adjacent to, or underneath the LTM8021.

LTM8021

OUT

BIAS

ADJ

8021 F03

OUT

4V TO 36V

RUN/SS

GND

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

For more information www.linear.com/LTM8021

PLANE

GND V

ADJ

RUN/SS

OUT

BIAS

Figure 4. Layout Showing Suggested External Components, GND Plane and Thermal Vias

8021fd

Page 11

applicaTions inForMaTion

LTM8021

LOW

IMPEDANCE

ENERGIZED

24V SUPPLY

CLOSING SWITCH

SIMULATES HOT PLUG

STRAY INDUCTANCE DUE TO 6 FEET (2 METERS) OF TWISTED PAIR

22µF AI.EI.

LTM8021

4.7µF

20V/DIV

10A/DIV

DANGER

RINGING V ABSOLUTE MAXIMUM RATING

20µs/DIV

MAY EXCEED

(5a)

LTM8021

4.7µF

(5b)

20V/DIV

10A/DIV

20µs/DIV

0.7Ω LTM8021

4.7µF0.1µF

(5c)

Figure 5. Ensures Reliable Operation When the LTM8021 is Connected to a Live Supply

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

small size, robustness and low impedance of ceramic

The 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

20V/DIV

10A/DIV

20µs/DIV

8021 F05

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

8021fd

For more information www.linear.com/LTM8021

Page 12

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 40.3cm

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:

– Thermal resistance from junction to ambient.

JCbottom

– Thermal resistance from junction to the bottom

of the product case.

– Thermal resistance from junction to top of the

JCtop

product case.

– 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:

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.

JCbottom

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.

is determined with nearly all of the component power

JCtop

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 θ

JCbottom

, this value may be useful for comparing packages but the test conditions don’t generally match the user’s application.

8021fd

For more information www.linear.com/LTM8021

Page 13

applicaTions inForMaTion

LTM8021

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 θ

JCbottom

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

JUNCTION-TO-AMBIENT RESISTANCE (JESD 51-9 DEFINED BOARD)

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.

JUNCTION-TO-CASE (TOP)

RESISTANCE

JUNCTION AMBIENT

µMODULE DEVICE

JUNCTION-TO-BOARD RESISTANCE

JUNCTION-TO-CASE

(BOTTOM) RESISTANCE

Figure 6. Thermal Model of µModule Regulator

CASE (BOTTOM)-TO-BOARD

RESISTANCE

CASE (TOP)-TO-AMBIENT

RESISTANCE

BOARD-TO-AMBIENT

RESISTANCE

8021 F06

For more information www.linear.com/LTM8021

8021fd

Page 14

LTM8021

(mA)

600

Typical applicaTions

0.8V Step-Down Converter

VIN*

3.4V TO 36V

1µF

*RUNNING VOLTAGE RANGE. PLEASE REFER TO THE APPLICATIONS INFORMATION SECTION FOR START-UP DETAILS.

LTM8021

BIAS

RUN/SS

GND ADJ

OUT

100µF

VIN*

7V TO 36V

OUT

0.8V AT 500mA

8021 TA02

5V Step-Down Converter

LTM8021

RUN/SS

GND ADJ

1µF

1.8V Step-Down Converter

VIN*

3.4V TO 36V

1µF

*RUNNING VOLTAGE RANGE. PLEASE REFER TO THE APPLICATIONS INFORMATION SECTION FOR START-UP DETAILS.

OUT

BIAS

19.1k

OUT

5V AT 500mA

2.2µF

LTM8021

BIAS

RUN/SS

GND ADJ

OUT

100µF

78.7k

OUT

1.8V AT 500mA

8021 TA03

–5V Positive-to-Negative Converter Load Current vs Input Voltage

VIN*

3.75V TO 31V

*RUNNING VOLTAGE RANGE. PLEASE REFER TO THE APPLICATIONS INFORMATION SECTION FOR START-UP DETAILS.

1µF

LTM8021

RUN/SS

GND ADJ

*RUNNING VOLTAGE RANGE. PLEASE REFER TO THE APPLICATIONS INFORMATION SECTION FOR START-UP DETAILS.

OUT

BIAS

4.7µF

19.1k

OPTIONAL SCHOTTKY CLAMP

–5V

8021 TA05

LOAD

500

400

300

200

100

8021 TA04

10 20

15 25

VIN (V)

8021 TA05b

8021fd

For more information www.linear.com/LTM8021

Page 15

package DescripTion

LGA 35 0113 REV B

Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.

LGA Package

35-Lead (11.25mm × 6.25mm × 2.82mm)

(Reference LTC DWG # 05-08-1805 Rev B)

aaa Z

11.250 BSC

2.72 – 2.92

LTM8021

2.540

1.270

0.0000

0.9525

1.270

1.5875

2.540

PAD 1

CORNER

4.445

3.175

1.905

SUGGESTED PCB LAYOUT

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

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

5. PRIMARY DATUM -Z- IS SEATING PLANE

6. THE TOTAL NUMBER OF PADS: 35

7 PACKAGE ROW AND COLUMN LABELING MAY VARY

AMONG µModule PRODUCTS. REVIEW EACH PACKAGE LAYOUT CAREFULLY

SYMBOL

aaa

bbb

TOLERANCE

0.15

0.10

PACKAGE TOP VIEW

0.0000

0.635

0.9525

0.3175

TOP VIEW

1.905

3.175

4.445 SEE NOTES

0.605 – 0.665

5.080 BSC

PADS

1.270 BSC

COMPONENT

PIN “A1”

TRAY PIN 1

6.250 BSC

aaa Z

DETAIL A

PACKAGE SIDE VIEW

0.605 – 0.665

H B AD C

LTMXXXXXX

BEVEL

PACKAGE IN TRAY LOADING ORIENTATION

PACKAGE BOTTOM VIEW

µModule

2.40 – 2.60

8.890 BSC

MOLD

DETAIL A

bbb Z

CAP

SUBSTRATE

0.27 – 0.37

PAD 1 C (0.30)

SEE NOTES

For more information www.linear.com/LTM8021

8021fd

Page 16

LTM8021

package DescripTion

LTM8021 Pinout (Sorted by Pin Number)

PIN SIGNAL DESCRIPTION

A1 RUN/SS

A2 ADJ

A4 V

A5 V

B1 GND

B2 GND

B4 V

B5 V

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 V

F4 V

F5 V

G1 GND

G2 GND

G3 V

G4 V

G5 V

H1 GND

H2 GND

H3 BIAS

H4 V

H5 V

OUT

8021fd

For more information www.linear.com/LTM8021

Page 17

LTM8021

revision hisTory

REV DATE DESCRIPTION PAGE NUMBER

D 3/14 Updated thermal resistance values

Updated Order Information table Updated Thermal Considerations section

(Revision history begins at Rev D)

2 2

12, 13

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.

For more information www.linear.com/LTM8021

8021fd

Page 18

LTM8021

package phoTo

Typical applicaTion

3.3V Step-Down Converter

VIN*

5.5V TO 36V

1µF 4.7µF

*RUNNING VOLTAGE RANGE. PLEASE REFER TO THE APPLICATIONS INFORMATION SECTION FOR START-UP DETAILS.

LTM8021

RUN/SS

GND ADJ

OUT

BIAS

32.4k

OUT

3.3V AT 500mA

8021 TA06

relaTeD parTs

PART NUMBER DESCRIPTION COMMENTS

LTM4600 10A DC/DC µModule

LTM4600HVMPV Military Plastic 10A DC/DC µModule

LTM4601/ LTM4601A

12A DC/DC µModule with PLL, Output Tracking/Margining and 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

LTM4604 4A Low V

DC/DC µModule

LTM4605 5A to 12A Buck-Boost µModule High Efﬁciency, Adjustable Frequency, 4.5V ≤ V

LTM4607 5A to 12A Buck-Boost µModule High Efﬁciency, Adjustable Frequency, 4.5V ≤ V

LTM4608 8A Low V

DC/DC µModule

LTM8020 36V, 200mA DC/DC µModule

LTM8022 1A, 36V DC/DC µModule

LTM8023 2A, 36V DC/DC µModule

Basic 10A DC/DC µModule, 15mm × 15mm × 2.8mm LGA

–55°C to 125°C Operation, 15mm × 15mm × 2.8mm LGA

Synchronizable, PolyPhase

Operation, LTM4601-1 Version Has No

Remote Sensing

Synchronizable, PolyPhase Operation, LTM4603-1 Version Has No Remote Sensing, Pin-Compatible with the LTM4601

2.375V ≤ V

≤ 5V, 0.8V ≤ V

≤ 5V, 9mm × 15mm × 2.3mm LGA

OUT

16V, 15mm × 15mm × 2.8mm

25V, 15mm × 15mm × 2.8mm

2.375V ≤ V

4V ≤ V

Adjustable Frequency, 0.8V ≤ V

≤ 5V, 0.8V ≤ V

≤ 36V, 1.25V ≤ V

≤ 5V, 9mm × 15mm × 2.8mm LGA

OUT

≤ 5V, 6.25mm × 6.25mm × 2.3mm LGA

OUT

≤ 5V, 11.25mm × 9mm × 2.82mm,

OUT

Pin-Compatible to the LTM8023

Adjustable Frequency, 0.8V ≤ V

≤ 5V, 11.25mm × 9mm × 2.82mm,

OUT

Pin-Compatible to the LTM8022

≤ 20V, 0.8V ≤ V

≤ 36V, 0.8V ≤ V

OUT

≤

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ● FAX: (408) 434-0507

For more information www.linear.com/LTM8021

●

www.linear.com/LTM8021

8021fd

LT 0314 REV D • PRINTED IN USA

 LINEAR TECHNOLOGY CORPORATION 2008