Datasheet

LTC4089-3
12
40893f
For more information www.linear.com/4089-3
I
IN
I
LOAD(mA)
0
300
400
500
400 500300
40893 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
40893 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
40893 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 Limit
Whenever the input power path is enabled (i.e., SUSP =
0V and HVIN = 0V) and power is available at IN, power
is delivered to OUT. The current limit and charger control
circuits of the LTC4089-3 are designed to limit input cur-
rent 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
CL
=
1000
R
CLPROG
• V
CLPROG






=
1000V
R
CLPROG
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 film resistors are recommended.
The programmed battery charge current, I
CHG
, is
defined as:
I
CHG
=
50,000
R
PROG
• V
PROG






=
50,000V
R
PROG
Figure 2. Input and Battery Currents as a Function of Load Current
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:
I
IN
= I
OUT
+ I
BAT
=
V
CLPROG
R
CLPROG
• 1000
The current limiting circuitry in the LTC4089-3 can and
should be configured to limit current to 500mA for USB
applications (selectable using the HPWR pin and pro-
grammed using the CLPROG pin).
The LTC4089-3 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-
fifth 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-fifth of the limit when HPWR is low). Even if
the battery charge current is set to exceed the allowable
USB current, the USB specification will not be violated.
(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