ACT3780 datasheet(8/20 Pages) ACTIVE-SEMI

8 / 20 page

ACT3780

Rev 8, 09-Jul-13

Innovative PowerTM

- 8 -

www.active-semi.com

Active-Semi Proprietary―For Authorized Recipients and Customers

ActivePath

TM is a trademark of Active-Semi.

(1)

FUNCTIONAL DESCRIPTION

The ACT3780 is a complete battery-charging and

system power management solution for portable

hand-held equipment using single-cell Lithium-

based batteries. The ACT3780 incorporates Active-

Semi's

patent-pending

ActivePath

architecture

which automatically selects the best available input

supply for the system, and additionally features a

complete,

high-accuracy

(±0.5%),

thermally

regulated, Full-Featured single cell linear Li+

charger with an integrated 12V power MOSFET.

ActivePath

Architecture

Active-semi's proprietary ActivePath architecture

performs three important functions:

System Configuration Optimization

Depending upon the state of the input supply,

ActivePath

automatically optimizes the power

system configuration. If the input supply is

present, ActivePath powers the system in parallel

with the battery, so that both system power and

charge current can be independently managed to

ensure that system power requirements are

satisfied, the battery can charge as quickly as

possible, and to ensure that the total system current

does not exceed the capability of the input supply. If

the input supply is not present, then ActivePath

automatically configures the system to draw

power from the battery. Finally, if the system

current requirement exceeds the capability of the

input supply, ActivePath automatically configures

the battery to support the load in parallel with the

input

supply,

ensure

maximum

supply

capability

the

load

under

peak-power

consumption conditions.

Input MOSFET Power (Q1)

At the input of the ACT3780's ActivePath circuit is

Q1, an integrated 12V power MOSFET. Q1 is part

of an internal low-dropout linear regulator that

regulates the system voltage (VSYS) to 4.6V,

protecting the system from high-voltage input

supplies. Q1 includes several features that can be

used to limit the total current drawn from the input

supply.

ACIN's current limit is determined primarily by the

ACIN input, Q1 operates in “AC-Mode” when ACIN

is driven to a logic-high, and Q1 operates in “USB-

Mode” when driven to a logic-low. When operating

in “AC-Mode”, Q1's internal current limit is

programmed to 2.5A. When operating in “USB-

Mode”, Q1's current limit is set to either 450mA,

when CHGLEV is driven to a logic-high, or to 90mA,

when CHGLEV is driven to a logic-low. This

functionality

provides

simple

means

implementing a solution that operates within the

current-capability limitations of the USB port while

taking advantage of the high output current

capability of AC adapters. For more information

about the ACIN input, see the ACIN and CHGLEV

Inputs section.

Dual-Function MOSFET (Q2)

Q2 is a dual-function power MOSFET, that serves

both as a low-resistance (50mΩ) switch that

supplies the load current requirements of the

system from the battery when no input supply is

present or the system demands more current than

the input can provide.

Current-Limits and Charge-Current

Programming

ACT3780 provides a flexible current programming

scheme that combines the convenience of internal

charge current programming with the flexibility of

resistor-based

charge

current

programming.

Current limits and charge current programming are

managed as a function of the ACIN and CHGLEV

pins, in combination with RISET, the resistance

connected to the ISET pin.

ACIN and CHGLEV Inputs

ACIN is a logic input that configures the current-limit

of input transistor (Q1) as well as that of the battery

charger. ACIN features an logic input threshold, so

that the input voltage detection threshold may be

adjusted with a simple resistive voltage divider. This

input also allows a simple, low-cost dual-input

charger switch to be implemented with just a few,

low-cost components. As shown in the Functional

Block Diagram.

When ACIN is driven to a logic high, the ActivePath

operates in “AC-Mode” and the charger charges at

the current programmed by RISET,

When ACIN is driven to a logic-low, the ActivePath

circuitry operates in “USB-Mode”, which enforces a

maximum charge current setting of 450mA, if

CHGLEV is driven to a logic-high, or 90mA, if

CHGLEV is driven to a logic-low.

ISET(mA) = 495 / (RISET(kΩ) - 0.036)

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