LTC4088 LINER [Linear Technology], LTC4088 Datasheet - Page 11

• Manufacturer Part Number: LTC4088
• Description: High Effi ciency Battery Charger/USB Power Manager
• Manufacturer: LINER [Linear Technology]

load current will be drawn from the battery via the ideal
diodes even when the battery charger is enabled.
The current at CLPROG is a precise fraction of the V
current. When a programming resistor and an averaging
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 1.188V and power
delivered by the switching regulator is held constant.
Several ratios of current are available which can be set
to correspond to USB low and high power modes with a
single programming resistor.
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 pro-
gramming resistor according to the following expression:
where I
V
R
h
the sample current delivered to CLPROG. Refer to the
Electrical Characteristics table for values of h
V
the USB specifi cation for the average input current of 1x
or 5x mode will not be violated, provided that R
2.94k or greater.
Table 1 shows the available settings for the D0, D1 and
D2 pins.
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
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
OPERATIO
CLPROG
CLPROG
CLPROG
CLPROG
I
VBUS
BUSQ
=
is the ratio of the measured current at V
and I
is the CLPROG servo voltage in current limit,
is the value of the programming resistor and
I
BUSQ
is the quiescent current of the LTC4088,
BUSQ
+
U
R
V
. Given worst-case circuit tolerances,
CLPROG
CLPROG
OUT
to approximately 300mV above
•
(
h
CLPROG
OUT
+
. These modes
1
)
CLPROG
CLPROG
BUS
BUS
to
is
,
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, V
fi xed 3.6V as shown in Figure 2. This 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
range between the no-load voltage and slighly below the
battery voltage, indicated by the shaded region of Figure 2.
If there is no battery present when this happens, V
collapse to ground.
The voltage regulation loop compensation is controlled by
the capacitance on V
required for loop stability. Additional capacitance beyond
this value will improve transient response.
Table 1. Controlled Input Current Limit
D0
0
0
0
0
1
1
1
1
4.5
4.2
3.9
3.6
3.3
3.0
2.7
2.4
2.4
D1
0
0
1
1
0
0
1
1
2.7
NO LOAD
Figure 2. V
OUT
3.0
D2
. An MLCC capacitor of 10µF is
0
1
0
1
0
1
0
1
BAT (V)
3.3
OUT
CHARGER
vs BAT
3.6
STATUS
300mV
On
Off
On
Off
On
Off
Off
Off
OUT
3.9
LTC4088
4088 F02
will regulate at a
2.5mA (Susp High)
500µA (Susp Low)
4.2
BUS
100mA (1x)
100mA (1x)
500mA (5x)
500mA (5x)
I
1A (10x)
1A (10x)
BUS(LIM)
, V
OUT
11
OUT
may
will
4088f