LTC4160 datasheet(13/32 Pages) LINER

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LTC4160/LTC4160-1

41601f

OPERATION

Introduction

The LTC4160/LTC4160-1 are high efﬁciency bidirectional

switching power managers and Li-Ion/Polymer battery

chargers designed to make optimal use of the power

available while minimizing power dissipation and easing

thermal budgeting constraints. The innovative PowerPath

architecture ensures that the end product application is

powered immediately after external voltage is applied,

even with a completely dead battery, by prioritizing power

to the end product.

When acting as a step-down converter, the LTC4160/

LTC4160-1’s bidirectional switching regulator takes power

from USB, wall adapters, or other 5V sources and provides

power to the end product application and efﬁciently charges

the battery using Bat-Track. Because power is conserved,

the LTC4160/LTC4160-1 allow the load current on VOUT to

exceed the current drawn by the USB port, making maxi-

mum use of the allowable USB power for battery charging.

For USB compatibility, the switching regulator includes

a precision average input current limit. The bidirectional

switching regulator and battery charger communicate to

ensure that the average input current never exceeds the

USB speciﬁcations.

In addition, the bidirectional switching regulator can also

operate as a 5V synchronous step-up converter, taking

power from VOUT and delivering up to 500mA to VBUS

without the need for any additional external components.

This enables systems with USB dual-role transceivers to

function as USB On-The-Go dual-role devices. True output

disconnect and average output current limit features are

included for short circuit protection.

The LTC4160/LTC4160-1 contain both an internal 180mΩ

ideal diode as well as an ideal diode controller for use

with an external P-channel MOSFET. The ideal diodes

from BAT to VOUT guarantee that ample power is always

available to VOUT even if there is insufﬁcient 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.

The LTC4160/LTC4160-1 also feature an overvoltage pro-

tection circuit which is designed to work with an external

N-channel MOSFET to prevent damage to their inputs

caused by accidental application of high voltage.

Finally, to prevent battery drain when a device is con-

nected to a suspended USB port, an LDO from VBUS to

VOUT provides low power USB suspend current to the end

product application.

Bidirectional PowerPath Switching Regulator –

Step-Down Mode

The power delivered from VBUS to VOUT is controlled by

a 2.25MHz constant frequency bidirectional switching

regulator in step-down mode. VOUT drives the combination

of the external load and the battery charger. To meet the

maximum USB load speciﬁcation, the switching regulator

contains a measurement and control system that ensures

that the average input current remains below the level

programmed at CLPROG.

If the combined load does not cause the switching regu-

lator to reach the programmed input current limit, VOUT

will track approximately 0.3V above the battery voltage.

By keeping the voltage across the battery charger at this

low level, power lost to the battery charger is minimized.

Figure 1 shows the power ﬂow in step-down mode.

If the combined external load plus battery charge current

is large enough to cause the switching regulator to reach

the programmed input current limit, the battery charger

will reduce its charge current by precisely the amount

necessary to enable the external load to be satisﬁed. Even

if the battery charge current is programmed to exceed the

allowable USB current, the USB speciﬁcation for average

input current will not be violated; the battery charger will

reduce its current as needed. Furthermore, if the load cur-

rent at VOUT exceeds the programmed power from VBUS,

load current will be drawn from the battery via the ideal

diode(s) even when the battery charger is enabled.

The current out of CLPROG is a precise fraction of the VBUS

current. When a programming resistor and an averaging

capacitor are connected from CLPROG to GND, the volt-

age on CLPROG represents the average input current of

the switching regulator. As the input current approaches

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