ACT88320 datasheet(26/57 Pages) QORVO

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Data Sheet Rev. E, November 2019 | Subject to change without notice

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ACT88320

Advanced PMU with Inrush Control and Bypass Switch

STEP-DOWN DC/DC CONVERTERS

General Description

The

ACT88320

contains

three

fully

integrated

step-down converters. Buck1 is a 4A output, while

Buck2 and Buck3 are 2.5A outputs. All buck converters

are

fixed

frequency,

current-mode

controlled,

synchronous PWM converters that achieve peak

efficiencies of up to 95%. The buck converters switch

1.125MHz

2.25MHz

and

are

internally

compensated, requiring only three small external

components (Cin, Cout, and L) for operation. The buck

regulators minimize noise in sensitive applications with

the use of a switching phase delay and offset.

Additionally, all regulators are available with a variety of

standard and custom output voltages, and may be

software-controlled via the I2C interface for systems that

require advanced power management functions.

The ACT88320 buck regulators are highly configurable

and can be quickly and easily reconfigured via I2C. This

allows

them

support

changes

hardware

requirements without the need for PCB changes.

Examples of I2C functionality are given below:

Real-time power good, OV, and current limit status

Ability to mask individual faults

Dynamically change output voltage

On/Off control

Softstart ramp

Switching delay and phase control

Low power mode

Overcurrent thresholds

Refer to the Active-Semi Application Note describing the

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

optimize 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 I2C 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 I2C 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 I2C register

VSET0 in normal operation and by VSET1 in DVS mode.

Buck1 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 I2C VOUTx register. The VOUTx

registers contain an unsigned 8-bit binary value. As an

example,

Buck

1’s

VOUT0

contains

01000000b (128 decimal), the output voltage is 1.8V.

The Buck1 output voltage range can also be configured

to the same range as Buck2/3 via a custom CMI.

Buck2/3 are programmable between 0.8V to 3.9875V in

12.5mV steps

Vbuck2 = 0.8V + VOUTx * 0.0125V

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