ACT5830 datasheet(17/41 Pages) ACTIVE-SEMI

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STEP-DOWN DC/DC CONVERTER

ACT5830

Rev 2, 20-Jan-11

Innovative Power

- 17 -

www.active-semi.com

ActivePMU

TM is a trademark of Active-Semi.

2CTM is a trademark of NXP.

FUNCTIONAL DESCRIPTIONS

General Description

REG

fixed-frequency,

current-mode,

synchronous PWM step-down converters that

achieves a peak efficiency of up to 97%. REG is

capable of supplying up to 350mA of output current

and operates with a fixed frequency of 1.6MHz,

minimizing noise in sensitive applications and

allowing the use of small external components.

REG is available with a variety of standard and

custom output voltages, and may be software-

controlled via the I2C interface by systems that

require advanced power management functions.

100% Duty Cycle Operation

REG is capable of operating at up to 100% duty

cycle. During 100% duty-cycle operation, the high-

side power MOSFET is held on continuously,

providing a direct connection from the input to the

output (through the inductor), ensuring the lowest

possible

dropout

voltage

battery-powered

applications.

Synchronous Rectification

REG features an integrated n-channel synchronous

rectifier, which maximizes efficiency and minimizes

the total solution size and cost by eliminating the

need for an external rectifier.

Enabling and Disabling REG

Enable/disable functionality is typically implemented

as part of a controlled enable/disable scheme

utilizing nMSTR and other system control features

of the ACT5830. REG is automatically enabled

whenever either of the following conditions are met:

1) HF_PWR is asserted high, or

2) PWR_ON is asserted high, or

3) PWR_HOLD is asserted high.

When none of these conditions are true, or if

REG/ON[ ] bit is set to [0], REG is disabled, and its

quiescent supply current drops to less than 1µA.

Programming the Output Voltage

By default, REG powers up and regulates to its

default output voltage. Once the system is enabled,

REG’s output voltage may be programmed to a

different value, typically in order to reduce the

power consumption of a microprocessor in standby

mode. Program the output voltage via the I2C serial

interface by writing to the REG/VSET[ ] register.

Programmable Operating Mode

By default, REG operates in fixed-frequency PWM

mode at medium to heavy loads, then transitions to

a proprietary power-saving mode at light loads in

order to save power. In applications where low

noise is critical, force fixed-frequency PWM

operation across the entire load current range, at

the expense of light-load efficiency, by setting the

REG/MODE[ ] bit to [1].

Power-OK

REG features a power-OK status bit that can be

read by the system microprocessor. If the output

voltage is lower than the power-OK threshold,

typically 6% below the programmed regulation

voltage, REG/OK[ ] will clear to 0.

Soft-Start

REG includes internal soft-start circuitry, and

enabled its output voltage tracks an internal 80µs

soft-start ramp so that it powers up in a monotonic

manner that is independent of loading.

Compensation

REG utilizes current-mode control and a proprietary

internal compensation scheme to simultaneously

simplify external component selection and optimize

transient performance over its full operating range.

No compensation design is required, simply follow a

few simple guidelines described below when

choosing external components.

Input Capacitor Selection

The input capacitor reduces peak currents and

noise induced upon the voltage source. A 2.2µF

ceramic input capacitor is recommended for most

applications.

Output Capacitor Selection

For most applications, a 10µF ceramic output

capacitor is recommended. Although REG was

designed to take advantage of the benefits of

ceramic capacitors, namely small size and very-low

ESR, low-ESR tantalum capacitors can provide

acceptable results as well.

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