LTC4055 Linear Technology, LTC4055 Datasheet - Page 14

• Manufacturer Part Number: LTC4055
• Description: USB Power Controller and Li-Ion Linear Charger
• Manufacturer: Linear Technology

OPERATIO
LTC4055
USB CURRENT LIMIT AND CHARGE CURRENT
CONTROL
The current limit and charger control circuits of the LTC4055
are designed to limit input current as well as control
battery charge current as a function of I
grammed current limit, I
The programmed battery charge current, I
as:
Input current, I
current and the OUT pin output current.
The current limiting circuitry in the LTC4055 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).
When programmed for 500mA current limit and 500mA or
more of charging current, powered from IN1/IN2 and
battery charging is active, control circuitry within the
14
–100
600
500
400
200
100
300
I
I
I
CL
CHG
IN
0
0
= I
(2a) High Power Mode/Full Charge
OUT
100
R
R
50 000
CLPROG
50 000
R
PROG
+ I
PROG
,
,
200
IN
BAT
, is equal to the sum of the BAT pin output
= R
I
I
U
LOAD
IN
300
CLPROG
•
•
(mA)
V
V
PROG
CLPROG
400
CL
I
I
CHARGING
LOAD
BAT
= 100k
is defined as:
500
Figure 2. Input and Battery Currents as a Function of Load Current
(IDEAL DIODE)
4055 F02a
50 000
R
I
R
600
50 000
,
BAT
PROG
CLPROG
,
V
120
100
–20
V
80
40
20
60
CHG
OUT
0
0
(2b) Low Power Mode/Full Charge
, is defined
. The pro-
(R
20
PROG
40
= R
I
I
IN
LOAD
CLPROG
60
I
CHARGING
(mA)
BAT
LTC4055 reduces the battery charging current such that
the sum of the battery charge current and the load current
does not exceed 500mA (100mA when HPWR is low, see
Figure 2) The battery charging current goes to zero when
load current exceeds 500mA (80mA when HPWR is low).
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.
PROGRAMMING CURRENT LIMIT
The formula for current limit is:
where V
the total resistance from the CLPROG pin to ground.
For example, if typical 500mA current limit is required,
calculate:
In USB applications, the minimum value for R
should be 105k. This will prevent the application current
from exceeding 500mA due to LTC4055’s tolerances and
I
LOAD
80
I
R
= 100k)
CL
CLPROG
100
CLPROG
(IDEAL DIODE)
I
CLPROG
4055 F02b
I
120
BAT
500
is the CLPROG pin voltage and R
•
1
V
50 000
–100
mA
600
500
400
200
100
300
0
,
0
•
(R
I
50 000 100
CL
(2c) High Power Mode with
PROG
100
I
,
BAT
= 500mA and I
R
V
= I
CLPROG
CLPROG
= 200k, R
CHG
200
CHARGING
I
I
I
BAT
IN
LOAD
300
(mA)
•
k
CLPROG
50 000
CHG
400
I
BAT
I
LOAD
,
= 250mA
= I
= 100k)
CL
500
(IDEAL DIODE)
CLPROG
– I
4055 F02c
OUT
CLPROG
I
600
BAT
4055p
is