LTC4009-2_15 Datasheet, PDF (17/28 Pages) Linear Technology – High Efficiency, Multi-Chemistry Battery Charger

LTC4009
LTC4009-1/LTC4009-2
Applications Information
Programming LTC4009-1/LTC4009-2 Output Voltage
The LTC4009-1/LTC4009-2 feature precision internal bat-
tery voltage feedback resistor taps configured for common
lithium-ion voltages. All that is required to program the
desired voltage is proper pin programming of FVS0 and
FVS1 as shown in Table 3.
Table 3. LTC4009-1/LTC4009-2 Output Voltage Programming
V_BAT VOLTAGE
LTC4009-1
LTC4009-2
FVS1
FVS0
4.1V
4.2V
GND
GND
8.2V
8.4V
GND
INTV_DD
12.3V
12.6V
INTV_DD
GND
16.4V
16.8V
INTV_DD
INTV_DD
Programming Input Current Limit
To set the input current limit, I_LIM, the minimum wall
adapter current rating must be known. To account for the
tolerance of the LTC4009 input current sense circuit, 5%
should be subtracted from the adapter’s minimum rated
output. Refer to Figure 6 and program the input current
limit function with the following equation.
R_CL
=
100mV
I_LIM
where I_LIM is the desired maximum current draw from
the DC (adapter) input, including adjustments for toler-
ance, if any.
Often an AC adapter will include a rated current output
margin of at least +10%. This can allow the adapter cur-
rent limit value to simply be programmed to the actual
minimum rated adapter output current. Table 4 shows
some common R_CL current limit programming values.
A lowpass filter formed by R_F (5.1k) and C_F (0.1µF) is
required to eliminate switching noise from the LTC4009
PWM and other system components. If input current limit-
ing is not desired, CLN should be shorted to CLP while
CLP remains connected to power.
FROM DC
POWER INPUT
C_DC 10k
R_CL
C_F 0.1µF
R_F
5.1k
TO REMAINDER
OF SYSTEM
2
1
CLP
CLN
LTC4009
4009 F06
Figure 6. Programming Input Current Limit
Table 4. Common R_CL Values
ADAPTER
RATING
R_CL VALUE (1%)
0.50A
0.200Ω
0.75A
0.133Ω
1.00A
0.100Ω
1.25A
0.080Ω
1.50A
0.067Ω
1.75A
0.057Ω
2.00A
0.050Ω
R_CL POWER
DISSIPATION
0.050W
0.075W
0.100W
0.125W
0.150W
0.175W
0.200W
R_CL POWER
RATING
0.25W
0.25W
0.25W
0.25W
0.25W
0.25W
0.25W
Figure 7 shows an optional circuit that can influence the
parameters of the input current limit in two ways. The
first option is to lower the power dissipation of R_CL at the
expense of accuracy without changing the input current
DCIN
CLP 2
LTC4009
CLN 1
D1
INPUT DIODE
C_F
0.22µF
R_CL
R_F
1%
2.49k 1%
TO REMAINDER
OF SYSTEM
INTV_{DD 17}
R2
Q1
IMX1
Q2
2SC2412
R1
R3 = R1
1%
1%
4009 F07
Figure 7. Adjusting Input Current Limit
4009fd
17