LTC4098-1 datasheet(17/32 Pages) LINER

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LTC4098/LTC4098-1

40981fb

MOSFET will be in full conduction. If additional conduc-

tance is needed, an external P-channel MOSFET transistor

may be added from BAT to VOUT. The IDGATE pin of the

LTC4098/LTC4098-1 drives the gate of the external P-chan-

nel MOSFET transistor for automatic ideal diode control.

The source of the external P-channel MOSFET should be

connected to VOUT and the drain should be connected to

BAT. Capable of driving a 1nF load, the IDGATE pin can

control an external P-channel MOSFET transistor having

an on-resistance of 30m

Ω or lower. Figure 5 shows the

decreased forward voltage compared to a conventional

Schottky diode.

Suspend LDO

The LTC4098/LTC4098-1 provide a small amount of power

to VOUTin suspend mode by including an LDO from VBUS to

VOUT. This LDO will prevent the battery from running down

when the portable product has access to a suspended USB

port. Regulating at 4.6V, this LDO only becomes active when

the switching converter is disabled. In accordance with the

USB speciﬁcation, the input to the LDO is current limited so

that it will not exceed the low power or high power suspend

speciﬁcation. If the load on VOUT exceeds the suspend cur-

rent limit, the additional current will come from the battery

via the ideal diodes. The suspend LDO sends a scaled copy

of the VBUS current to the CLPROG pin, which will servo to

approximately 100mV in this mode. Thus, the high power

and low power suspend settings are related to the levels

programmed by the same resistor for 1x and 5x modes.

Battery Charger

The LTC4098/LTC4098-1 include a constant-current/con-

stant-voltage battery charger with automatic recharge,

automatic termination by safety timer, low voltage trickle

charging, bad cell detection and thermistor sensor input

for out-of-temperature charge pausing.

When a battery charge cycle begins, the battery charger

ﬁrst determines if the battery is deeply discharged. If the

battery voltage is below VTRKL,typically2.85V,anautomatic

trickle charge feature sets the battery charge current to

10% of the programmed value. If the low voltage persists

for more than 1/2 hour, the battery charger automatically

terminates and indicates, via the CHRG pin, that the bat-

tery was unresponsive.

Once the battery voltage is above VTRKL, the charger begins

charging in full power constant-current mode. The current

delivered to the battery will try to reach 1030V/RPROG.

Depending on available input power and external load

conditions, the battery charger may or may not be able to

charge at the full programmed rate. The external load will

always be prioritized over the battery charge current. The

USB current limit programming will always be observed

and only additional power will be available to charge the

battery. When system loads are light, battery charge cur-

rent will be maximized.

FORWARD VOLTAGE (mV) (BAT – VOUT)

600

1800

2000

2200

120

240 300

40981 F05

200

1400

1000

400

1600

1200

800

180

360

480

420

VISHAY Si2333

EXTERNAL

IDEAL DIODE

LTC4098/

LTC4098-1

IDEAL DIODE

SEMICONDUCTOR

MBRM120LT3

Figure 5. Ideal Diode V-I Characteristics

OPERATION

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