LINEAR TECHNOLOGY LTM4608 Technical data

8A Low Voltage, Low Profi le DC/DC µModule Regulator in
9mm × 15mm Package Weighs Only 1g

Design Note 430

Eddie Beville and Alan Chern

Introduction

In communications, industrial and other high power
systems, board-mounted point-of-load (POL) DC/DC
power supplies simplify thermal management and offer
high performance. An ideal POL power supply module
takes a minimal amount of space and mounts on the
board much like other surface mount ICs without special
tooling. It should also demonstrate exceptional thermal
performance with excellent effi ciency and low power
dissipation.

8A DC/DC μModule™ Regulator in an IC Form Factor
The LTM4608® μModule regulator is a complete high

density power supply in a low profi le (15mm × 9mm ×

2.8mm) LGA surface mount package (Figure 1). Its small
form factor houses the switching controller, MOSFETs,
inductor and all suppor t components, and weighs only 1g.
At this size, it can be mounted on the back side of a system
board, taking advantage of otherwise unused space.

and a frequency spread spectrum feature can also be
activated to further reduce switching noise harmonics.
The device supports output voltage tracking or simpler
supply rail sequencing. Programmable output voltage
margining is supported for ±5%, ±10%, and ±15% levels.
Fault protection features include over voltage protection,
over current protection, and thermal shutdown.

Quick and Easy Design

Figure 2 shows a typical 1.8V output design; its effi ciency
is shown in Figure 3. Because the LTM4608 includes
two integrated 10μF ceramic capacitors, additional input
capacitors are only needed for large load steps up to
the full 8A level. Linear Technology provides a μModule

, LT, LTC and LTM are registered trademarks of Linear Technology. μModule and
SwitcherCAD are trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.

V

3V TO 5.5V

V

IN

V

IN

SV

IN

SW

LTM4608

RUN

PLLLPF

TRACK

CLKOUT GND

CLKIN

V

I

PGOOD

MGN

SGND

OUT

THM

FB

4.87k

I

TH

DN430 F02

OUT

1.8V
8A

100μF10μF

Figure 1. The LTM4608 Offers High Power Density
in a 9mm × 15mm × 2.8mm LGA Package

The LTM4608 operates from an input supply range of

2.375 to 5.5V, and a single resistor is all that is needed to
set the output voltage within a 0.6V to 5V output range.
Its high effi ciency design and low thermal impedance
package delivers up to 8A continuous current.

Wealth of Features

The LTM4608’s 1.5MHz switching frequency and current
mode architecture allow it to react quickly to line and load
transients without sacrifi cing stability. Cycle-by-cycle
current mode control also enables excellent current shar­ing for parallel operation. The integrated clock enables
multiphase operation and frequency synchronization,

12/07/430

Figure 2. Few Components Are
Required for a 1.8V/8A Application

100

95

90

85

EFFICIENCY (%)

80

75

70

0

VIN = 3.3V

= 5V

V

IN

V

= 1.8V

2468

LOAD CURRENT (A)

OUT

DN430 F03

10

Figure 3. Effi ciency of the Application in Figure 2

Power Design tool and SwitcherCAD™ simulation tool
to calculate the necessary capacitance for any particular
design (www.linear.com/micromodule).

For low output voltage ripple and low droop during load
transients, low ESR capacitors should be used. A low
ESR polymer or ceramic capacitor is suffi cient. Typical
ranges are 100μF to 200μF. The output voltage is set with
an external resistor from the FB pin to ground.

Thermally Enhanced Packaging

The LTM4608’s package has a low thermal resistance of
7°C/W junction-to-pin and 25°C/W junction-to-ambient
when mounted on a four-layer board with no airfl ow. The
device’s unique packaging allows simple heat sinking
from both the top and bot tom, making it possible to use
a metal chassis as a heat sink.

Output Voltage Tracking

Output voltage tracking is programmed via the Track
pin. The slave output can be tracked up and down with
another regulator’s output.

Current Sharing: 8A + 8A = 16A

Two or more LTM4608 μModule regulators can be paral­leled to provide multiples of 8A of load current. Because

of the LTM4608’s current mode architecture, the output
current and power are evenly an d safely distributed acros s
each LTM4608. Figure 4 shows a 16A design that also
operates 180° out-of-phase to reduce input and output
ripple current.

Fault Conditions: Overcurrent Limit and Thermal
Shutdown

The LTM4608’s current mode control inherently limits
cycle-by-cycle inductor current, not only in steady state
operation, but also in transient. The LTM4608 device
has over temperature shutdown protection that inhibits
switching operation above 150°C.

Conclusion

Weighing 1g, occupying 135mm2, and standing only

2.8mm tall, the LTM4608 is a complete and effi cient
point-of-load DC/DC system that eases circuit and layout
challenges by fi tting in the tightest spaces even on the
bottom of the PCB. With the LTM4608, the design of an
8A switchmode regulator is as simple as a linear regula­tor. This DC/DC μModule regulator is rich in features and
provides circuit protection as well as capability to current
share for applications requiring more than 8A.

Data Sheet Download

www.linear.com/micromodule

3V TO 5.5V

V

IN

10μF

RUN

TRACK

C2
10μF

V

IN

SV

IN

SW

LTM4608

RUN

PLLLPF

TRACK

MODE

PHMODE

CLKOUT GND

V

IN

SV

IN

SW

LTM4608

RUN

PLLLPF

TRACK

MODE

PHMODE

CLKOUT GND

CLKIN

CLKIN

V

I

PGOOD

BSEL

MGN

SGND

V

I

PGOOD

BSEL

MGN

SGND

OUT

THM

OUT

THM

FB

I

TH

V

OUT

FB

I

TH

V

OUT

DN430 F04

Figure 4. Two LTM4608s in Parallel, 1.5V at 16A

V

OUT

C1
100μF

6.3V
X5R

1.5V
16A

100pF

C4

3.32k

100μF

6.3V
X5R

C3
100μF

6.3V
X5R

For applications help,

call [phone], Ext. 2593

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

[phone]

●

FAX: [phone] ● www.linear.com

dn430f LT/TP 1207 305K • PRINTED IN THE USA

© LINEAR TECHNOLOGY CORPORATION 2007