ACT81460
Rev 1.0, 18-Dec-2018
The boost can operate in a dual constant voltage/cur-
rent mode. Either the voltage or current loop dominates,
depending on the operating conditions. In this mode,
both the voltage and current regulation loops are active.
As long as the load current is less than the current reg-
ulation threshold, the voltage loop dominates and main-
tains a constant output voltage. If the load current in-
creases to the current regulation threshold, the current
loop takes over and reduces the output voltage to main-
tain a constant current. This mode is similar to a lab
power supply with a fixed voltage output setting and a
maximum current limit setting. The output voltage is
sensed at the VBST pin. The current is sensed by the
ISNS pin, which is always regulated to 0.25V
BOOST STEP-UP REGULATOR
General Description
The ACT81460 contains a fully integrated boost con-
verter. It can boost the battery voltage up to 20V and
provide up to 40mA of output current. The maximum al-
lowable output current is dependent on the battery and
output voltages. The boost is very versatile and can be
used for many different applications such as driving a
LED backlight, driving audio speakers, implementing
audio functions such as audio beeps, or haptics for
communicative feedback.
The boost operates with high efficiency and achieve a
peak efficiency up to 95%. It is internally compensated,
requiring only three external components (Cin, Cout,
and L) for operation. The ACT81460 boost regulator is
highly configurable and can be quickly and easily recon-
figured via I2C. This allows it to support changes in hard-
ware requirements without the need for PCB changes.
This mode is useful for driving LEDs that do not have
their own power source. Configure the boost for this
mode by connecting the output of the boost converter
(VBST pin) to the load, which is typically the anode of
an LED string. Then connect the cathode of the LED
string to the ISNS pin.
Operating Modes
Synchronous Rectification
The boost converter operates with a standard fixed fre-
quency. It can be operated with voltage feedback, cur-
rent feedback, or both.
The boost regulator features an integrated synchronous
rectifier (or low side FET), maximizing efficiency and
minimizing the total solution size and cost by eliminating
the need for external rectifiers.
Constant Voltage Feedback Mode
The boost can operate as a standard boost converter.
Configure the boost for this mode by leaving the ISNS
pin disconnected from the boost circuitry. The ISNS pin
can be operated separately and independently from the
boost converter.
Soft-Start
The boost regulator includes a fixed 80ms soft-start
ramp which limits the rate of change of the output volt-
age, minimizing input inrush current and ensuring that
the output powers up in a monotonic manner that is in-
dependent of loading on the output. This circuitry is ef-
fective any time the regulator is enabled, as well as after
responding to a short circuit or other fault condition.
In constant voltage (CV) mode, the boost can supply up
to 40mA. The maximum current should be reduced to
25mA when the output voltage is > 17V.
Constant Current Feedback Mode
The boost converter’s synchronous FET is connected
between the BSTSW pin (switch node) and the VBST
pin (output voltage). Because of this, there is no way to
disconnect the output voltage from the input source.
When the VSYS voltage softstarts, the VSYS voltage
passes through the synchronous FET and charges up
the boost converter output voltage. VBST then stays at
the VSYS voltage until the boost converter is enabled.
After the boost converter is enabled, the output voltage
ramps to the setpoint with the 80ms softstart time.
The boost can operate as a current sink. In this config-
uration, the boost is not needed. The ISNS pin sinks a
constant current, regardless of the voltage applied to it.
This mode is useful for driving LEDs that have another
power source. Configure the boost for this mode by con-
necting the external circuit directly to the ISNS pin. The
boost converter can be operated separately and inde-
pendently from the ISNS pin. Note that the ISNS pin al-
ways regulates to 0.25V.
Output Voltage Setting
In constant current mode (CV) mode, the output can
drive up to 40mA. The more LEDs, the higher the re-
quired output voltage. If the voltage across the LEDs
exceeds 17V, the maximum current should be reduced
to 25mA.
The boost converter regulates to the voltage defined by
I2C register VSET. It can be programmed between 5V
and 20.75V in 250mV steps. The following equation cal-
culates the output voltage based on the VSET register
setting.
Constant Voltage/Current Feedback Mode
Vboost = 5V + VSET * 0.25V
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