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LTC4099

4099f

Introduction

The LTC4099 is an I2C controlled power manager and Li-

Ion charger designed to make optimal use of the power

available from a variety of sources while minimizing power

dissipation and easing thermal budgeting constraints. The

innovative PowerPath architecture ensures that the ap-

plication is powered immediately after external voltage is

applied, even with a completely dead battery, by prioritizing

power to the application.

The LTC4099 includes a Bat-Track monolithic step-down

switching regulator for USB, wall adapters and other 5V

sources. Designed speciﬁcally for USB applications, the

switching regulator incorporates a precision average in-

put current limit for USB compatibility. Because power is

conserved, the LTC4099 allows the load current on VOUT to

exceed the current drawn by the USB port making maximum

use of the allowable USB power for battery charging. The

switching regulator and battery charger communicate to

ensure that the average input current never exceeds the

USB speciﬁcations.

For automotive and other high voltage applications, the

LTC4099 provides Bat-Track control of an external Linear

Technologystep-downswitchingregulatortomaximizebat-

tery charger efﬁciency and minimize heat production.

When power is available from both the USB and an aux-

iliary input, the auxiliary input is prioritized.

The LTC4099 contains 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 VOUTeven

if there is insufﬁcient or absent power at VBUS or WALL.

The LTC4099 features an overvoltage protection circuit

which is designed to work with an external N-channel

MOSFET to prevent damage to its input caused by ac-

cidental application of high voltage.

To prevent battery drain when a device is connected to a

suspended USB port, an LDO from VBUS to VOUT provides

either a low power or high power USB suspend current

to the application.

Finally, the LTC4099 has considerable adjustability built

in so that power levels and status information can be

controlled and monitored via a simple two wire I2C port.

Bat-Track Input Current Limited Step-Down Switching

Regulator

The power delivered from VBUS to VOUT is controlled by a

2.25MHz constant-frequency step-down switching regu-

lator. To meet the maximum USB load speciﬁcation, the

switching regulator contains a measurement and control

system which ensures that the average input current re-

mains below the level programmed at the CLPROG pin

and I2C port. VOUT drives the combination of the external

load and the battery charger.

If the combined load does not cause the switching power

supply 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 path components.

If the combined external load plus battery charge current

is large enough to cause the switching power supply 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 satis-

ﬁed. Even if the battery charge current is programmed to

exceed the allowable USB power, the USB speciﬁcation

for average input current will not be violated; the battery

charger will reduce its current as needed. Furthermore, if

the load current at VOUT exceeds the programmed power

from VBUS, the extra load current will be drawn from the

battery via the ideal diodes 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 av-

eraging capacitor are connected from CLPROG to GND,

the voltage on CLPROG represents the average input

current of the switching regulator. As the input current

approaches the programmed limit, CLPROG reaches

1.18V and power delivered by the switching regulator

is held constant.

The input current limit has eight possible settings rang-

ing from the USB suspend limit of 500μA up to 1.2A

for wall adapter applications. Two of these settings are

speciﬁcally intended for use in the 100mA and 500mA

USB applications.

OPERATION

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