LTC4085EDE-3 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
LTC4085EDE-3
Linear Technology
'LTC4085EDE-3' PDF : 24 Pages View PDF
LTC4085-3/LTC4085-4
OPERATION
USB Current Limit and Charge Current Control
The current limit and charger control circuits of the
LTC4085 are designed to limit input current as well as
control battery charge current as a function of IOUT. The
programmed current limit, ICL, is defined as:
ICL
=
⎛
⎝⎜
1000
RCLPROG
•
⎞
VCLPROG ⎠⎟
=
1000V
RCLPROG
The programmed battery charge current, ICHG, is defined as:
ICHG
=
⎛
⎝⎜
50,000
RPROG
•
VPROG
⎞
⎠⎟
=
50,000V
RPROG
Input current, IIN, is equal to the sum of the BAT pin output
current and the OUT pin output current:
IIN = IOUT + IBAT
The current limiting circuitry in the LTC4085 can and should
be configured to limit current to 500mA for USB applica-
tions (selectable using the HPWR pin and programmed
using the CLPROG pin).
The LTC4085 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). 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.
600
120
600
IIN
500
IIN
100
500
IIN
400
80
400
ILOAD
ILOAD
ILOAD
300
60
300
IBAT = ICHG
200
IBAT
40
CHARGING
IBAT
200
CHARGING
IBAT
IBAT = ICL – IOUT
100
20
100
CHARGING
0
0
0
–100
0
–20
100 200 300 400 500 600
0
ILOAD (mA)
IBAT
(IDEAL DIODE)
408534 F02a
–100
20 40 60 80 100 120
0 100 200 300 400 500 600
ILOAD (mA)
IBAT
(IDEAL DIODE)
ILOAD (mA)
IBAT
(IDEAL DIODE)
408534 F02b
408534 F02c
(2a) High Power Mode/Full Charge
RPROG = 100k and RCLPROG = 2k
(2b) Low Power Mode/Full Charge
RPROG = 100k and RCLPROG = 2k
(2c) High Power Mode with
ICL = 500mA and ICHG = 250mA
RPROG = 100k and RCLPROG = 2k
Figure 2: Input and Battery Currents as a Function of Load Current
14
408534fb
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