Datasheet

LTC4089/LTC4089-5
12
40895fc
I
IN
I
LOAD(mA)
0
300
400
500
400 500300
4089 F02a
200
100
100 200
0
CURRENT (mA)
I
LOAD
I
BAT
(CHARGING)
I
BAT
(IDEAL DIODE)
I
IN
I
LOAD(mA)
0
60
80
100
80 10060
4089 F02b
40
20
20 40
0
CURRENT (mA)
I
LOAD
I
BAT
(CHARGING)
I
BAT
(IDEAL DIODE)
I
LOAD (mA)
0
300
400
500
400 500300
4089 F02c
200
100
100 200
0
CURRENT (mA)
I
IN
I
LOAD
I
BAT
= I
CHG
I
BAT
= I
CL
= I
OUT
I
BAT
(CHARGING)
I
BAT
(IDEAL DIODE)
input current as well as control battery charge current
as a function of I
OUT
. The input current limit, I
CL
, can be
programmed using the following formula:
I
R
V
V
R
CL
CLPROG
CLPROG
CLPROG
=
⎡
⎣
⎢
⎤
⎦
⎥
=
1000 1000
•
where V
CLPROG
is the CLPROG pin voltage (typically 1V)
and R
CLPROG
is the total resistance from the CLPROG pin
to ground. For best stability over temperature and time,
1% metal fi lm resistors are recommended.
The programmed battery charge current, I
CHG
, is
defi ned as:
I
R
V
V
R
CHG
PROG
PROG
PROG
=
⎡
⎣
⎢
⎤
⎦
⎥
=
50 000 50 000,
•
,
Input current, I
IN
, is equal to the sum of the BAT pin
output current and the OUT pin output current. V
CLPROG
will typically servo to 1V, however, if I
OUT
+ I
BAT
< I
CL
then V
CLPROG
will track the input current according to the
following equation:
II I
V
R
IN OUT BAT
CLPROG
CLPROG
=+= •1000
The current limiting circuitry in the LTC4089/LTC4089-5
can and should be confi gured to limit current to 500mA
Figure 2. Input and Battery Currents as a Function of Load Current
for USB applications (selectable using the HPWR pin and
programmed using the CLPROG pin).
The LTC4089/LTC4089-5 reduces battery charge current
such that the sum of the battery charge current and the
load current does not exceed the programmed input current
limit (one-fi fth of the programmed input current limit when
HPWR is low, see Figure 2). The battery charge current
goes to zero when load current exceeds the programmed
input current limit (one-fi fth of the limit when HPWR is
low). Even if the battery charge current is set to exceed
the allowable USB current, the USB specifi cation will not
be violated. The battery charger will reduce its current as
needed to ensure that the USB specifi cation is not exceeded.
If the load current is greater than the current limit, the
output voltage will drop to just under the battery voltage
where the ideal diode circuit will take over and the excess
load current will be drawn from the battery.
In USB applications, the minimum value for R
CLPROG
should be 2.1k. This will prevent the input current from
exceeding 500mA due to LTC4089/LTC4089-5 tolerances
and quiescent currents. A 2.1k CLPROG resistor will give a
typical current limit of 476mA in high power mode (HPWR
= 1) or 95mA in low power mode (HPWR = 0).
When SUSP is driven to a logic high, the input power
path is disabled and the ideal diode from BAT to OUT will
supply power to the application.
(a) High Power Mode/Full Charge
R
PROG
= 100k and R
CLPROG
= 2k
(b) Low Power Mode/Full Charge
R
PROG
= 100k and R
CLPROG
= 2k
(c) High Power Mode with
I
CL
= 500mA and I
CHG
= 250mA
R
PROG
= 200k and R
CLPROG
= 2k
OPERATION