ACT8600 datasheet(38/50 Pages) ACTIVE-SEMI

38 / 50 page

ACT8600

Rev 3, 15-Nov-12

Innovative Power

ActivePMU

TM and ActivePathTM are trademarks of Active-Semi.

2CTM is a trademark of NXP.

- 38 -

www.active-semi.com

General Description

REG1, REG2 and REG3 are fixed-frequency,

current-mode,

synchronous

PWM

step-down

converters that achieves peak efficiencies of up to

97%. These regulators operate with a fixed frequency

2.22MHz,

minimizing

noise

sensitive

applications and allowing the use of small external

components. Additionally, REG1, REG2 and REG3

are available with a variety of standard and custom

output voltages, and may be software-controlled via

the I2C interface for systems that require advanced

power management functions.

Output Current Capability

REG1, REG2, and REG3 are capable of supplying

1200mA, 1200mA and 950mA output current,

respectively.

100% Duty Cycle Operation

REG1, REG2 and REG3 are capable of operating at

up to 100% duty cycle. During 100% duty cycle

operation, the high-side power MOSFETs are held on

continuously, providing a direct connection from the

input to the output (through the inductor), ensuring

the lowest possible dropout voltage in battery

powered applications.

Operating Mode

By default, REG1, REG2, and REG3 operate in

fixed-frequency PWM mode at medium to heavy

loads, then transition to a proprietary power-saving

mode at light loads in order to save power.

Synchronous Rectification

REG1, REG2, and REG3 each feature integrated

synchronous rectifiers, maximizing efficiency and

minimizing the total solution size and cost by

eliminating the need for external rectifiers.

Soft-Start

REG1, REG2 and REG3 include internal 500 us soft-

start ramps which limit the rate of change of the

output voltage, minimizing input inrush current and

ensuring that the output powers up in a monotonic

manner that is independent of loading on the outputs.

This circuitry is effective any time the regulator is

enabled, as well as after responding to a short-circuit

or other fault condition.

Compensation

REG1, REG2 and REG3 utilize current-mode control

and a proprietary internal compensation scheme to

simultaneously simplify external component selection

and optimize transient performance over their full

operating range. No compensation design is

required; simply follow a few simple guide lines

described

below

when

choosing

external

components.

Input Capacitor Selection

The input capacitor reduces peak currents and noise

induced upon the voltage source. A 4.7μF ceramic

capacitor is recommended for each regulator in most

applications.

Output Capacitor Selection

REG1, REG2 and REG3 were designed to take

advantage of the benefits of ceramic capacitors,

namely small size and very-low ESR. REG1, REG2

and REG3 are designed to operate with 22uF output

capacitor over most of their output voltage ranges,

although

capacitance

may

desired

depending on the duty cycle and load step

requirements.

Inductor Selection

REG1, REG2, and REG3 utilize current-mode control

and a proprietary internal compensation scheme to

simultaneously simplify external component selection

and optimize transient performance over their full

operating range. These devices were optimized for

operation with 3.3μH inductors, although inductors in

the 2.2μH to 4.7μH range can be used.

Configuration Options

Output Voltage Programming

By default, REG1, REG2 and REG3 power up and

regulate to their default output voltages. Once the

system is enabled, the output voltages may be

modified through either the I2C interface by writing to

the VSET[ ] register. Using I2C, the output voltage

may be programmed to any voltage as shown in

Table 4.

Interrupts

REG1, REG2 and REG3 may optionally interrupt the

processor if their output voltages fall out regulation.

Enable interrupts by setting a regulator’s nFLTMSK[ ]

bit.

STEP-DOWN DC/DC REGULATORS

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