LTC4098-1 datasheet(14/32 Pages) LINER

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LTC4098/LTC4098-1

40981fb

The switching input regulator can also be deactivated

(USB suspend).

The average input current will be limited by the CLPROG pro-

gramming resistor according to the following expression:

VBUS

VBUSQ

CLPROG

()

•1

where IVBUSQ is the quiescent current of the LTC4098/

LTC4098-1, VCLPROG is the CLPROG servo voltage in

current limit, RCLPROG is the value of the programming

resistor and hCLPROG is the ratio of the measured current

at VBUS to the sample current delivered to CLPROG. Refer

to the Electrical Characteristics table for values of hCLPROG,

VCLPROG and IVBUSQ. Given worst-case circuit tolerances,

the USB speciﬁcation for the average input current in 1x

or 5x mode will not be violated, provided that RCLPROG is

3.01k or greater.

Table 1 shows the available settings for the D0, D1 and

D2 pins.

Table 1. Controlled Input Current Limit

CHARGER

STATUS

IBUS(LIM)

100mA (1x)

1A (10x)

500mA (5x)

Off

500μA (Susp Low)

Off

100mA (1x)

Off

1A (10x)

Off

500mA (5x)

Off

2.5mA (Susp High)

BAT (V)

2.4

4.5

4.2

3.9

3.6

3.3

3.0

2.7

2.4

3.3

3.9

40981 F02

2.7

3.0

3.6

4.2

NO LOAD

300mV

Figure 2. VOUT vs BAT

Notice that when D0 is high and D1 is low, the switching

regulator is set to a higher current limit for increased

charging and power availability at VOUT. These modes will

typically be used when there is line power available from

a wall adapter.

While not in current limit, the switching regulator’s

Bat-Track feature will set VOUT to approximately 300mV

above the voltage at BAT. However, if the voltage at BAT

is below 3.3V, and the load requirement does not cause

the switching regulator to exceed its current limit, VOUT

will regulate at a ﬁxed 3.6V, as shown in Figure 2. This

instant-on operation will allow a portable product to run

immediately when power is applied without waiting for

the battery to charge.

If the load does exceed the current limit at VBUS, VOUT

will range between the no-load voltage and slighly below

the battery voltage, indicated by the shaded region of

Figure 2.

OPERATION

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