Datasheet

17
4009fd
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
FVS1 FVS0LTC4009-1 LTC4009-2
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
mV
I
CL
LIM
=
100
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.
Table 4. Common R
CL
Values
ADAPTER
RATING R
CL
VALUE (1%)
R
CL
POWER
DISSIPATION
R
CL
POWER
RATING
0.50A
0.200Ω
0.050W 0.25W
0.75A
0.133Ω
0.075W 0.25W
1.00A
0.100Ω
0.100W 0.25W
1.25A
0.080Ω
0.125W 0.25W
1.50A
0.067Ω
0.150W 0.25W
1.75A
0.057Ω
0.175W 0.25W
2.00A
0.050Ω
0.200W 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
Figure 6. Programming Input Current Limit
2 1
R
CL
C
DC
C
F
0.1µF
CLP
LTC4009
CLN
R
F
5.1k
4009 F06
10k
FROM DC
POWER INPUT
TO REMAINDER
OF SYSTEM
2
1
CLP
DCIN
CLN
17
INTV
DD
LTC4009
R
CL
1%
R3 = R1
1%
R1
1%
Q2
2SC2412
R
F
2.49k 1%
R2
Q1
IMX1
4009 F07
C
F
0.22µF
D1
INPUT DIODE
TO REMAINDER
OF SYSTEM
Figure 7. Adjusting Input Current Limit