LINEAR TECHNOLOGY LTC3562 Technical data

Compact I2C-Controllable Quad Synchronous Step-Down
DC/DC Regulator for Power-Conscious Portable Processors

Design Note 442

Jim Drew

Introduction

The LTC®3562 quad output step-down regulator is designed
for multicore handheld microprocessor applications that
operate from a single Li-Ion bat tery. Its four monolithic, high
effi cienc y buck regulators suppor t Intel’s mobile CPU P-State
and C-State energy saving operating modes. The output

2

voltages are independently controllable via I

C, and each
output can be indep endently star ted and shut down. Design­ers can choose from power saving pulse-skipping mode or
Burst Mode

®

operation, or select low noise LDO mode. The
space-saving LTC3562 is available in a 3mm × 3mm QFN
package and requires few external components.

Four I2C-Controllable Regulators

Two of the regulators provide up to 600mA of output
current each while the other two provide up to 400mA
each. All regulators are internally compensated, so no
external compensation components are needed.

One of the 60 0mA regulators and one of t he 400mA regula-

2

tors (R600 A and R400A) feature I

C-controllable feedback
voltages, as shown in Figure 1. The output voltages of
these “Type A” regulators are set by a combination of ex-

2

ternal programming resistors and I

C-adjustable feedback

voltages—16 settings from 425mV to 800mV.

The “Type B” regula tors (R600B and R40 0B) do not require
extern al programming resistors bec ause the resistors are
integrated on-chip. The values of the internal feedback

2

resistors are adjusted through the I

C port, resulting in
128 possible output voltages from 600mV to 3.775V in
25mV increments.

Inrush current limiting is provided by soft-start circuitry
in all four regulators, as well as short-circuit protection
and switch node slew rate limiting to reduce EMI.

Power Saving Operating Modes

The LTC3562’s step-dow n regulators offer four sel ectable
modes of operation, which make it possible to balance
low noise against effi ciency. The four operating modes
of the LTC3562 are shown in Figure 2.

At moderate to heavy loads, the constant frequency
pulse-skipping mode provides the best output switching
noise solution. At lighter loads, ei ther Burst Mode operation
o r f o r c e d B u r s t M o d e o p e r a t i o n c a n b e s e l e c t e d t o m a x i m i z e
effi ciency, though these modes produce higher ripple.

If the application calls for the lowest possible noise,
LDO mode can be used for up to 50mA of load current.

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

05/08/442

V

OUT

400A

1.5V

400mA

OUT

400B

1.2V

400mA

+

10pF10

μF

10

10

μF

SCL SDA DV

V

IN

RUN400A

SW400A

475k

536k

4.7μH

μF

LTC3562

FB400A

SW400B
OUT400B OUT600B

PGND AGND

POR600A

SW600A

FB600A

RUN600A

SW600B

3562 TA01

CC

100k

3.3

μH4.7μH

3.3μH

Li-Ion/Polymer

3.4V TO 4.2V

V

Figure 1. High Effi ciency Quad Step-Down Converter with I2C Control

MICROPROCESSOR

634k

499k

V

OUT

3.3V
600mA

μF

10

SDA
SCL
DV

POR

10pF

600B

CC

V

600A

OUT

1.8V
600mA

10μF

All four converters support 100% duty cycle operation
when the input voltage drops very close to the output
voltage setting.

OUT 400B = 3.3V

LDO Mode

OUT 600B = 2.5V

Forced Burst Mode

OUT 600A = 1.5V

Burst Mode

OUT 400A = 1.2V

Pulse Skip Mode

which ramps down with the fi rst. This is repeated until
each output has tracked down to a minimum value and
then disabled.

The ability to adjust the output voltage on the fl y is also
useful to margin the supplies for design evaluation or
manufacturing quality audit testing. Voltage margining
is applied to the nominal operating voltages in Figure 3
and Figure 4.

Reducing the voltage or shutting down any output can
reduce battery life or reduce energy usage in ‘green’
applications.

Figure 2. Modes of Operation

I2C Programming of Output Voltages Allows Easy
Sequencing, Tracking and Margining

Each output can be programmed on the fl y and indepen­dently enabled or disabled. These features taken together
enable almost any sequencing or tracking scheme. A
sequencing example is shown in Figure 3.

OUT 400B = 3.3V

OUT 600B = 2.5V

OUT 600A = 1.5V

OUT 400A = 1.2V

Figure 3. LTC3562 Voltage Sequencing and Margining

A coincident voltage tracking example is shown in Figure

4. All of the outputs are ramped up together at power up.
At power down, the highest out put is incrementally ramp ed
down until it reaches the value of the next higher voltage,

OUT 400B = 3.3V

OUT 600B = 2.5V

OUT 600A = 1.5V

OUT 400A = 1.2V

Figure 4. LTC3562 Voltage Tracking and Margining

Conclusion

The LTC3562 is a versatile high effi ciency quad output
monolithic synchronous buck regulator controlled with

2

C interface in a 3mm × 3mm QFN package. Four

an I
modes of operation allow the switching regulators to be
tailored to the system’s ef fi ciency and noise requirements.
This device is well suited for handheld microprocessor
applications operating from a single Li-Ion battery where

2

battery life is critical. The ability to use I

C to adjust
output voltages on the fl y or disable output voltages
supports Intel’s mobile CPU P-State and C-State energy
saving modes of operation and simplifi es development
and manufacturing tolerance testing.

Data Sheet Download

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