Datasheet

LTC4098-3.6
14
409836f
The input current limit is programmed by various com-
binations of the D0, D1 and D2 pins as shown in Table 1.
The switching input regulator can also be deactivated
(USB suspend).
The average input current will be limited by the CLPROG
programming resistor according to the following
expression:
II
V
R
h
VBUS VBUSQ
CLPROG
CLPROG
CLPROG
=+ +
()
•1
where I
VBUSQ
is the quiescent current of the LTC4098-3.6,
V
CLPROG
is the CLPROG servo voltage in current limit,
R
CLPROG
is the value of the programming resistor and
h
CLPROG
is the ratio of the measured current at V
BUS
to
the sample current delivered to CLPROG. Refer to the
Electrical Characteristics table for values of h
CLPROG
,
V
CLPROG
and I
VBUSQ
. Given worst-case circuit tolerances,
the USB specification for the average input current in 1x
or 5x mode will not be violated, provided that R
CLPROG
is
3.01k or greater.
Table 1 shows the available settings for the D0, D1 and
D2 pins.
Table 1. Controlled Input Current Limit
D2 D1 D0
CHARGER
STATUS I
BUS(LIM)
0 0 0 On 100mA (1x)
0 0 1 On 1A (10x)
0 1 0 On 500mA (5x)
0 1 1 Off 500µA (Susp Low)
1 0 0 Off 100mA (1x)
1 0 1 Off 1A (10x)
1 1 0 Off 500mA (5x)
1 1 1 Off 2.5mA (Susp High)
BAT (V)
2.4
4.0
3.8
3.4
3.2
3.0
2.8
2.6
2.4
3.3
409836 F02
3.6
2.7 3.0
3.6
V
OUT
(V)
NO LOAD
400mV
Figure 2. V
OUT
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 V
OUT
. 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 V
OUT
to approximately 400mV
above the voltage at BAT. However, if the voltage at BAT
is below 3.1V, and the load requirement does not cause
the switching regulator to exceed its current limit, V
OUT
will regulate at a fixed 3.5V, 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 V
BUS
, V
OUT
will range between the no-load voltage and slightly below
the battery voltage, indicated by the shaded region of
Figure 2.
OPERATION