Datasheet

LTC4160/LTC4160-1
14
41601f
OPERATION
the programmed limit, CLPROG reaches 1.18V and power
delivered by the switching regulator is held constant.
The input current limit is programmed by the I
LIM0
and
I
LIM1
pins. The input current limit has four possible set-
tings ranging from the USB suspend limit of 500μA up
to 1A for wall adapter applications. Two of these settings
are specifically intended for use in the 100mA and 500mA
USB application. Refer to Table 1 for current limit settings
using I
LIM0
and I
LIM1
.
Table 1. USB Current Limit Settings Using I
LIM0
and I
LIM1
I
LIM1
I
LIM0
USB SETTING
0 0 1x Mode (USB 100mA Limit)
0 1 10x Mode (Wall 1A Limit)
1 0 Low Power Suspend (USB 500μA Limit)
1 1 5x Mode (USB 500mA Limit)
When the switching regulator is activated, 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 LTC4160/
LTC4160-1, 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 cur-
rent 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 100mA or 500mA mode will not be violated,
provided that R
CLPROG
is 3.01k or greater.
While not in current limit, the switching regulator’s
Bat-Track feature will set V
OUT
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, V
OUT
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 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.
Figure 1. Power Path Block Diagram – Power Available from USB/Wall Adapter
+
–
+
+
–
0.3V
1.18V
3.6V
CLPROG
I
SWITCH
/N
+
–
+
–
15mV
OmV
IDEAL
DIODE
PWM AND
GATE DRIVE
AVERAGE V
BUS
INPUT
CURRENT LIMIT
CONTROLLER
V
BUS
VOLTAGE
CONTROLLER
V
OUT
VOLTAGE
CONTROLLER
+
–
5V
IDGATE
10
V
OUT
12
SW
3.5V TO
(BAT + 0.3V)
TO SYSTEM LOAD
SINGLE CELL
Li-Ion
41601 F01
14
BAT
USB INPUT
BATTERY POWER
11
TO USB
OR WALL
ADAPTER
+
V
BUS
+
–
6V
OVERVOLTAGE PROTECTION
×2
+
–
+
–
1V
BATTERY CHARGER
I
BAT
/1000
+
–
V
FLOAT
+
–
PROG
8
17
13
2
OVSENS
1
OVGATE