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LTC3586/LTC3586-1

3586fb

operaTion

Introduction

The LTC3586/LTC3586-1 are highly integrated power

management ICs which include a high efﬁciency switch

mode PowerPath controller, a battery charger, an ideal

diode, an always-on LDO, two 400mA buck switching

regulators, a 1A buck-boost switching regulator, and an

800mA boost switching regulator. All of the regulators can

be independently controlled via ENABLE pins.

Designed speciﬁcally for USB applications, the PowerPath

controller incorporates a precision average input current

buck switching regulator to make maximum use of the

allowable USB power. Because power is conserved, the

LTC3586/LTC3586-1 allow the load current on VOUT to

exceed the current drawn by the USB port without exceed-

ing the USB load speciﬁcations.

The PowerPath switching regulator and battery charger

communicatetoensurethattheinputcurrentneverviolates

the USB speciﬁcations.

The ideal diode from BAT to VOUT guarantees that ample

powerisalwaysavailabletoVOUTevenifthereisinsufﬁcient

or absent power at VBUS.

An always-on LDO provides a regulated 3.3V from avail-

able power at VOUT. Drawing very little quiescent current,

this LDO will be on at all times and can be used to supply

up to 20mA.

Along with constant frequency PWM mode, the buck and

the buck-boost switching regulators have a low power

burst mode setting for signiﬁcantly reduced quiescent

current under light load conditions.

High Efficiency Switching PowerPath Controller

Whenever VBUS is available and the PowerPath switch-

ing regulator is enabled, power is delivered from VBUS to

VOUT via SW. VOUT drives the combination of the external

load (including switching regulators 1, 2, 3 and 4) and

the battery charger.

If the combined load does not exceed the PowerPath

switchingregulator’sprogrammedinputcurrentlimit,VOUT

will track 0.3V above the battery (Bat-Track). By keeping

the voltage across the battery charger low, efﬁciency is

optimized because power lost to the linear battery char-

ger is minimized. Power available to the external load is

therefore optimized.

If the combined load at VOUT is large enough to cause the

switching PowerPath supply to reach the programmed

input current limit, the battery charger will reduce its

charge current by that amount necessary to enable the

external load to be satisﬁed. Even if the battery charge

current is set to exceedthe allowable USB current, the USB

speciﬁcation will not be violated. The PowerPath switch-

ing regulator will limit the average input current so that

the USB speciﬁcation is never violated. Furthermore, load

current at VOUT will always be prioritized and only excess

available power will be used to charge the battery.

If the voltage at BAT is below 3.3V, or the battery is not

present, and the load requirement does not cause the

PowerPath switching regulator to exceed the USB

speciﬁcation, VOUT will regulate at 3.6V, as shown in

Figure 1. This “instant-on” feature will allow a portable

product to run immediately when power is applied without

waiting for the battery to charge. If the load exceeds the

current limit at VBUS, VOUTwill range between the no-load

voltage and slightly below the battery voltage, indicated

by the shaded region of Figure 1.

For very low-battery voltages, the battery charger acts like

a load and, due to limited input power, its current will tend

topullVOUTbelowthe3.6V“instant-on”voltage.Toprevent

VOUT from falling below this level, an undervoltage circuit

automatically detects that VOUT is falling and reduces the

battery charge as needed. This reduction ensures that load

current and output voltages are always priortized while

allowing as much battery charge current as possible. See

Over-Programming the Battery Charger in Applications

Information Section.

The power delivered from VBUS to VOUT is controlled by a

2.25MHz constant-frequency buck switching regulator. To

meet the USB maximum load speciﬁcation, the switching

regulator includes a control loop which ensures that the

average input current is below the level programmed at

CLPROG.

LTC3586 Datasheet(PDF) 14 Page - Linear Technology

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