ACT8846 datasheet(36/63 Pages) QORVO

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ACT8846

Advanced PMU for Multi-core

Application Processors

Data Sheet Rev. 13.0, Nov. 11, 2019 | Subject to change without notice

36 of 63

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STEP-DOWN DC/DC REGULATORS

General Description

REG1, REG2, REG3, and REG4 are fixed-frequency,

current-mode, synchronous PWM step-down convert-

ers that achieves peak efficiencies of up to 97%. These

regulators operate with a fixed frequency of 2.25MHz,

minimizing noise in sensitive applications and allowing

the use of small external components. Additionally,

REG1, REG2, REG3, and REG4 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.

100% Duty Cycle Operation

REG1, REG2, REG3, and REG4 are capable of

operating at up to 100% duty cycle. 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, REG1, REG2, REG3, and REG4 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.

Synchronous Rectification

REG1, REG2, REG3, and REG4 each feature

integrated synchronous rectifiers, maximizing efficiency

and minimizing the total solution size and cost by

eliminating the need for external rectifiers.

Soft-Start

REG1, REG2, REG3, and REG4 include internal 400 us

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 ena-

bled, as well as after responding to a short-circuit or

other fault condition.

Compensation

REG1, REG2, REG3, and REG4 utilize current-mode

control and a proprietary internal compensation scheme

to simultaneously simplify external component selection

and optimize transient performance over their full oper-

ating range. No compensation design is required;

simply follow a few simple guide lines described below

when choosing external components.

Input Capacitor Selection

The input capacitor reduces peak currents and noise

induced upon the voltage source. A 10μF ceramic

capacitor is recommended for each regulator in most

applications.

Output Capacitor Selection

REG1, REG2, REG3, and REG4 were designed to take

advantage of the benefits of ceramic capacitors, namely

small size and very-low ESR. REG1, REG2, REG3 and

REG4 are designed to operate with 33uF or 44uF output

capacitor over most of their output voltage ranges,

although more capacitance may be desired depending

on the duty cycle and load step requirements.

Two of the most common dielectrics are Y5V and X5R.

Whereas Y5V dielectrics are inexpensive and can

provide high capacitance in small packages, their ca-

pacitance varies greatly over their voltage and temper-

ature ranges and are not recommended for DC/DC

applications. X5R and X7R dielectrics are more suitable

for output capacitor applications, as their characteristics

are more stable over their operating ranges, and are

highly recommended.

Inductor Selection

REG1, REG2, REG3, and REG4 utilize current-mode

control and a proprietary internal compensation scheme

to simultaneously simplify external component selection

and optimize transient performance over their full

operating range. These devices were optimized for

operation with 2.2μH or 1μH inductors. Choose an

inductor with a low DC-resistance, and avoid inductor

saturation by choosing inductors with DC ratings that

exceed the maximum output current by at least 30%.

Configuration Options

Output Voltage Programming

Figure 4:

OUT1 Output Voltage Programming

RFB1

RFB2

FB1

CFF

ACT8846

OUT1

ACT8846 Datasheet(PDF) 36 Page - Qorvo, Inc

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