ACT5830
Rev PrB, 05-Mar-08
STEP-DOWN DC/DC CONVERTER
FUNCTIONAL DESCRIPTIONS
Program the output voltage via the I2C serial inter-
face by writing to the REG/VSET[ ] register.
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.
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
100% Duty Cycle Operation
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Innovative PowerTM
- 17 -
www.active-semi.com
ActivePMUTM is a trademark of Active-Semi.
I2CTM is a trademark of Philips Electronics.
Copyright © 2008 Active-Semi, Inc.
ACTIVE-SEMI [ ACTIVE-SEMI, INC ]
