ACT5880
Rev 2, 03-Sep-13
STEP-DOWN DC/DC REGULATORS
General Description
Summary of key specifications
REG1 and REG2 are fixed-frequency, current-mode,
synchronous PWM step-down DC/DC converters that
achieve peak efficiencies of up to 97%. These
regulators operate at a fixed frequency around 2MHz,
minimizing noise in sensitive applications and
allowing the use of small external components.
Additionally, REG1 and REG2 are available with a
variety of standard and custom output voltages, and
may be software-controlled via the I2C interface for
Table 3:
Key Specifications of Step-down DC/DC
Converters
PARAMETER
VOLUME
Operation Voltage
2.7V to 5.5V
Active Mode Quiescent
Supply Current
65μA
systems that require advanced power management Sleep Mode Quiescent
23μA
1μA
Supply Current
functions. Finally, REG2 features a unique SLEEP
mode function that significantly reduces quiescent
power consumption yet maintains a regulated output
voltage that can supplies up to 10mA nominal (50mA
maximum).
Shutdown Current
1.2V and 1.2V/REG1, 1.8V/
REG2
Default Output Voltage
Output Range
0.6V to 3.9V
By default, REG1 and REG2 operate in fixed-
frequency PWM mode at medium to heavy load, then
transit to a proprietary power-saving mode at light
load for having better efficiency. In applications where
low noise is critical, fixed-frequency PWM operation
may be retained across the entire load current range
(in compromising of the light-load efficiency) by
setting the respective MODE[ ] bit via I2C.
1.2A/REG1, 0.6A/REG2
10mA/REG2 in Sleep Mode
Maximum Output Current
Soft-Start Step Transient
Both REG1 and REG2 implement constant slope
control for soft start ramping in 400μs nominal, as
well as the step up transition for outputting two
different voltages. This assures no overshoot during
start up and changes of voltages. The output
voltage drop is load condition dependent during
turning off or step down transition.
REG1 and REG2 are 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.
REG2 Sleep Mode
When set the EVENT4 bit of the system register,
the buck operation of REG2 stops and the linear
regulator unit starts smoothly with no dropping at
output. When the "Enable Key" is pressed or the
EVENT4 is cleared, the REG2 is set back to buck
operation and the linear regulation unit stops, also
in seamless smooth transition. The EVENT4 bit
should be cleared by software when wanting the
REG2 resumes from the sleep mode to normal
mode.
REG1 has 2 banks of registers for setting the output
voltage, with the VSEL input to select to output
voltage set in which bank.
REG2 has a buck unit and a synergetic linear
regulation unit, which is designed to replace the buck
unit in light load operation. The linear unit has almost
the same programmable features as an LDO, but
with a bit to program if to turn on when the buck is
tuned off, and it should not be set to active discharge
in shutdown.
When REG2 is set off before the set of EVENT4,
the assertion of EVENT4 starts REG2 in sleep
mode. In this condition the clear of EVENT4 sets
the REG2 off, without turning it into buck operation.
Manipulation
The output voltages and few other operation options
of REG1, the buck unit and synergetic linear unit in
REG2 are programmable through the I2C operation.
Refer to the REGISTER AND BIT DESCRIPTIONS
section for details and the step-down DC/DC
converter and LDO Voltage Setting for the code to
voltage cross.
Irregular Conditions
Both REG1 and REG2 are output short-circuit safe.
The over current protection and the over
temperature shutdown protection prevent the
ACT5880 from being damaged by thermal over
stress. When the output voltage drops about 7% off
the normal output voltage, the OK bit for the
regulator is cleared. When interrupt is unmasked,
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