ACT8865 datasheet(25/32 Pages) QORVO

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ACT8865

Advanced PMU for Atmel SAMA5Dx Series & SAM9 Series Processors

Data Sheet Rev. H, September 2019 | Subject to change without notice

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STEP-DOWN DC/DC REGULATORS

General Description

The

ACT8865

features

three

synchronous,

fixed-

frequency, current-mode PWM step down converters that

achieve peak efficiencies of up to 97%. REG1 and

REG2 are capable of supplying up to 1150mA of output

current, while REG3 supports up to 1300mA. These

regulators operate with a fixed frequency of 2MHz,

minimizing noise in sensitive applications and allowing

the use of small external components.

100% Duty Cycle Operation

Each regulator is 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

battery

powered

applications.

Synchronous Rectification

REG1, REG2, and REG3 each feature integrated n-

channel synchronous rectifiers, maximizing efficiency and

minimizing

the

total

solution

size

and

cost

eliminating the need for external rectifiers.

Soft-Start

When enabled, each output voltages tracks an internal

400μs soft-start ramp, minimizing input current during

startup and allowing each regulator to power up in a

smooth, monotonic manner that is independent of

output load conditions.

Compensation

Each buck regulator utilizes current-mode control and a

proprietary

internal

compensation

scheme

simultaneously simplify external component selection and

optimize transient performance over its full operating

range. No compensation design is required; simply

follow a few simple guidelines described below when

choosing external components.

Input Capacitor Selection

The input capacitor reduces peak currents and noise

induced upon the voltage source. A 4.7μF ceramic

capacitor is recommended for each regulator in most

applications.

Output Capacitor Selection

For most applications, 22μF ceramic output capacitors

are recommended for REG1/REG2/ REG3.

Despite the advantages of ceramic capacitors, care

must be taken during the design process to ensure

stable operation over the full operating voltage and

temperature range. Ceramic capacitors are available in a

variety of dielectrics, each of which exhibits different

characteristics that can greatly affect performance over

their temperature and voltage ranges.

Two of the most common dielectrics are Y5V and

X5R. Whereas Y5V dielectrics are inexpensive and can

provide

high capacitance

in small packages,

their

capacitance

varies

greatly

over

their

voltage

and

temperature 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, and REG3 utilize current-mode control and

proprietary

internal

compensation

scheme

simultaneously simplify external component selection and

optimize transient performance over their full operating

range. These devices were optimized for operation with

2.2μH inductors, although inductors in the 1.5μH to

3.3μH range can be used. 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%.

Enable / Disable Control

During normal operation, each buck may be enabled or

disabled via I2C interface by writing to that regulator's

ON[] bit. The regulator accepts rising or falling edge of

ON[] bit as on/off signal. To enable the regulator, clear

ON[] to 0 first then set to 1. To disable the regulator, set

ON[] to 1 first then clear it to 0.

REG1, REG2, REG3 Turn-On Delay

Each

REG1/REG2/REG3

features

programmable Turn-On Delay which help ensure a

reliable qualification. This delay is programmed by

DELAY[2:0], as shown in Table 5.

Operating

Mode

REG1, REG2, and REG3 each operate in fixed-

frequency PWM mode at medium to heavy loads

when MODE[ ] bit is set to 0, and transition to a

proprietary power-saving mode at light loads in order

to maximize standby battery life. In applications where

low noise is critical, force fixed- frequency PWM

operation across the entire load current range, at

the expense of light-load efficiency, by setting the

MODE[ ] bit to 1.

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