LTC4098-1 datasheet(16/32 Pages) LINER

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LTC4098/LTC4098-1

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With Bat-Track, battery charger efﬁciency is approximately:

ηη

TOTAL

BUCK

BAT

•

With the same assumptions as above, the total battery

charger efﬁciency is approximately 81%. This example

works out to less than 1W of power dissipation, or almost

60% less heat.

See the Typical Applications section for complete circuits

using the LT3653 and LT3480 with Bat-Track control.

Overvoltage Protection

The LTC4098/LTC4098-1 can protect itself from the inad-

vertent application of excessive voltage to VBUS or WALL

with just two external components: an N-channel FET and

a 6.04k resistor. The maximum safe overvoltage magnitude

will be determined by the choice of the external NMOS and

its associated drain breakdown voltage.

The overvoltage protection module consists of two pins.

The ﬁrst, OVSENS, is used to measure the externally ap-

plied voltage through an external resistor. The second,

OVGATE, is an output used to drive the gate pin of an

external FET. The voltage at OVSENS will be lower than

the OVP input voltage by (IOVSENS • 6.04k) due to the

OVP circuit’s quiescent current. The OVP input will be

200mV to 400mV higher than OVSENS under normal

operating conditions. When OVSENS is below 6V, an in-

ternal charge pump will drive OVGATE to approximately

1.88 • OVSENS. This will enhance the N-channel FET and

provide a low impedance connection to VBUS or WALL

which will, in turn, power the LTC4098/LTC4098-1. If

OVSENS should rise above 6V (6.35V OVP input) due to

a fault or use of an incorrect wall adapter, OVGATE will

be pulled to GND, disabling the external FET to protect

downstream circuitry. When the voltage drops below 6V

again, the external FET will be reenabled.

In an overvoltage condition, the OVSENS pin will be

clamped at 6V. The external 6.04k resistor must be sized

appropriately to dissipate the resultant power. For example,

a 1/10W 6.04k resistor can have at most √PMAX • 6.04kΩ

= 24V applied across its terminals. With the 6V at OVSENS,

the maximum overvoltage magnitude that this resistor can

withstand is 30V. A 1/4W 6.04k resistor raises this value

to 44V. WALL’s absolute maximum current rating of 10mA

imposes an upper protection limit of 66V.

The charge pump output on OVGATE has limited output

drive capability. Care must be taken to avoid leakage on

this pin, as it may adversely affect operation.

See the Applications Information section for examples of

multiple input protection, reverse input protection, and a

table of recommended components.

Ideal Diode from BAT to VOUT

The LTC4098/LTC4098-1 have an internal ideal diode as

well as a controller for an external ideal diode. Both the

internal and the external ideal diodes are always on and

will respond quickly whenever VOUT drops below BAT.

If the load current increases beyond the power allowed

from the switching regulator, additional power will be pulled

from the battery via the ideal diodes. Furthermore, if power

to VBUS (USB or wall power) is removed, then all of the

application power will be provided by the battery via the

ideal diodes. The ideal diodes will be fast enough to keep

VOUT from drooping with only the storage capacitance

required for the switching regulator. The internal ideal

diode consists of a precision ampliﬁer that activates a

large on-chip MOSFET transistor whenever the voltage at

VOUT is approximately 15mV (VFWD) below the voltage at

BAT. Within the ampliﬁer’s linear range, the small-signal

resistance of the ideal diode will be quite low, keeping

the forward drop near 15mV. At higher current levels, the

OPERATION

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