ACT88326
Advanced PMU with Bypass Switch,
& Pushbutton Function
Data Sheet Rev. 3.0, Nov. 11, 2019 | Subject to change without notice
26 of 45
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On/Off control
Softstart ramp
Switching delay and phase control
Low power mode
Overcurrent thresholds
Refer to the Active-Semi Application Note describing the
Register Map for full details on I
2
C functionality and
programming ranges.
100% Duty Cycle Operation
All buck converters are capable of 100% duty cycle
operation. During 100% duty cycle operation, the
high-side power MOSFETs are 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.
Operating Mode
By default, all buck converters operate in fixed-
frequency PWM mode at medium to heavy loads, then
transition to a proprietary power-saving mode at light
loads in order to save power. Power-save mode
reduces conduction losses by preventing the inductor
current from going negative.
To further optimize efficiency and reduce power losses
at extremely light loads, an additional lower power
mode, LPM, is available. LPM minimizes quiescent
current in between switching cycles. This reduces input
current by approximately 200µA in LPM mode. Light
load output voltage ripple increases from approximately
5mV to 10mV when in LPM mode. Light load voltage
droop when going from light load to heavier loads is only
increased by 2-3mV when in LPM mode. LPM allows
the customer to test the IC in their use case and opti-
mize the balance between power consumption, voltage
ripple, and transient response in their system. LPM is
enabled when I2C bits DISLPM = 0 and LP_MODE = 1.
The buck converters can also be forced to operate in
PWM mode at light load by setting I
2
C bit ForcePWM =
1. This results in slightly lower efficiency at light loads,
but improves transient response.
Synchronous Rectification
Buck1/2/3 each feature integrated synchronous
rectifiers (or LS FET drivers), maximizing efficiency and
minimizing the total solution size and cost by eliminating
the need for external rectifiers.
Soft-Start
Buck1/2/3 include internal 600us soft-start ramps which
limit the rate of change of the output voltage, minimizing
input inrush current and ensuring that the output powers
up in a monotonic manner that is independent of loading
on the outputs. This circuitry is effective any time the
regulator is enabled, as well as after responding to a
short-circuit or other fault condition. A single I
2
C register,
ALL_BUCKS_FASTER_SS, adjusts softstart between
600us when = 0 and 250us when = 1.
Output Voltage Setting
Buck1/2/3 regulate to the voltage defined by I
2
C register
VSET0 in normal operation and by VSET1 in DVS mode.
The ACT88326 has two output voltage programing
ranges.
Output range 1 is available to Buck1/2. This range can
be programmed between 0.6V and 2.991V in 9.376mV
steps.
Vbuck1=0.6 + VOUTx * 0.009376V
Where VOUTx is the decimal equivalent of the value in
each regulator’s I
2
C VOUTx register. The VOUTx
registers contain an unsigned 8-bit binary value. As an
example, if Buck 1’s VOUT0 register contains
01000000b (128 decimal), the output voltage is 1.8V.
Output range 2 is available to Buck1/2/3. This range can
be programmed between 0.8V to 3.9875V in 12.5mV
steps.
Vbuck1 = 0.8V + VOUTx * 0.0125V
See each IC’s CMI for its programing range. Note that
and IC’s default programming range cannot be changed.
Changing the programming range may result in
unexpected IC behavior.
Active Semi recommends that the buck converter’s out-
put voltage be kept /- 25% of the default output
voltage to maintain accuracy. Voltage changes larger
than +/- 25% may require different factory trim settings
(new CMI) to maintain accuracy.
DVS
Each buck converter supports Dynamic Voltage Scaling
(DVS). In normal operation for most CMI options, each
output regulates to the voltage programmed by its
VSET0 I
2
C register. During DVS, each output can be
programmed to regulate to its VSET1 voltage.
During the voltage transition between VSET0 to VSET1
and VSET1 to VSET0, the I
2
C bit FORCEPWM is set to
1 to force the buck converters into PWM mode. This
ensures that the output transition to the new voltage
(ES) Equipements Scientifiques SA - Département Composants & Modules - 127 rue de Buzenval BP 26 - 92380 Garches
Tél. 01 47 95 99 84 - Fax. 01 47 01 16 22 - e-mail: [email protected] - Site Web: www.es-france.com
