®
ACT5830
Rev 2, 20-Jan-11
STEP-DOWN DC/DC CONVERTER
FUNCTIONAL DESCRIPTIONS
mode. Program the output voltage via the I2C serial
interface by writing to the REG/VSET[ ] register.
General Description
REG is
a
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.
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
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,
typically 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,
providing a direct connection from the input to the
output (through the inductor), ensuring the lowest
possible dropout voltage in battery-powered
applications.
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.
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
choosing external components.
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.
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
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.
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
Innovative PowerTM
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