ACT8945A datasheet(32/46 Pages) QORVO

32 / 46 page

Data Sheet Rev. G, January 2020 | Subject to change without notice

32 of 46

www.qorvo.com

ACT8945A

Advanced PMU for Atmel SAMA5Dx Series & SAM9 Series Processors

STEP-DOWN DC/DC REGULATORS

General Description

The ACT8945A 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 1100mA of output

current, while REG3 supports up to 1200mA. 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 in 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 by

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

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 and 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 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 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%.

Configuration Options

Output Voltage Programming

By default, each regulator powers up and regulates to

its default output voltage. Output voltage is selectable

by setting VSEL pin that when VSEL is low, output

voltage is programmed by VSET1[ ] bits, and when

VSEL is high, output voltage is programmed by VSET2[

] bits. However, once the system is enabled, each

regulator's output voltage may

independently

programmed to a different value, typically in order to

minimize the power consumption of the microprocessor

during some operating modes. Program the output

voltages via the I

2C serial interface by writing to the

regulator's VSET1[ ] register if VSEL is low or VSET2

[ ] register if VSEL is high as shown in Table 5.

Enable / Disable Control

During normal operation, each buck may be enabled or

disabled via the I

2C interface by writing to that

regulator's ON[ ] bit. The regulator accept 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.

ACT8945A Datasheet(PDF) 32 Page - Qorvo, Inc

ACT8945A Datasheet(HTML) 32 Page - Qorvo, Inc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46

Datasheet Download

Link URL