ACT5830 datasheet(17/41 Pages) ACTIVE-SEMI

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STEP-DOWN DC/DC CONVERTER

ACT5830

Rev PrB, 05-Mar-08

Innovative Power

- 17 -

www.active-semi.com

ActivePMU

TM is a trademark of Active-Semi.

2CTM is a trademark of Philips Electronics.

FUNCTIONAL DESCRIPTIONS

General Description

REG is a fixed-frequency, current-mode, synchro-

nous 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 oper-

ates 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 manage-

ment 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, pro-

viding a direct connection from the input to the out-

put (through the inductor), ensuring the lowest pos-

sible dropout voltage in battery-powered applica-

tions.

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 utiliz-

ing 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 de-

fault output voltage. Once the system is enabled,

REG’s output voltage may be programmed to a dif-

ferent value, typically in order to reduce the power

consumption of a microprocessor in standby mode.

Program the output voltage via the I2C serial inter-

face 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 opera-

tion across the entire load current range, at the ex-

pense 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, typi-

cally 6% below the programmed regulation voltage,

REG/OK[ ] will clear to 0.

Soft-Start

REG includes internal soft-start circuitry, and en-

abled its output voltage tracks an internal 80µs soft-

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

ner 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 choos-

ing 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 ca-

pacitor is recommended. Although REG was de-

signed to take advantage of the benefits of ceramic

capacitors, namely small size and very-low ESR,

low-ESR tantalum capacitors can provide accept-

able results as well.

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