Datasheet

LTC4012/
LTC4012-1/LTC4012-2
18
4012fa
applications inForMation
Programming LTC4012-1/LTC4012-2 Output Voltage
The LTC4012-1/LTC4012-2 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. LTC4012-1/LTC4012-2 Output Voltage Programming
V
BAT
VOLTAGE
LTC4012-1 LTC4012-2 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 LTC4012 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 tolerance,
if any.
Figure 6. Programming Input Current Limit
2
1
R
CL
C
DC
C
F
0.1µF
CLP
LTC4012
CLN
R
F
5.1k
4012 F06
10k
FROM DC
POWER
INPUT
TO
REMAINDER
OF SYSTEM
3
INFET
2
1
CLP
CLN
17
INTV
DD
LTC4012
R
CL
1%
R3 = R1
1%
R1
1%
Q2
2SC2412
R
F
2.49k 1%
R2
Q1
IMX1
4012 F07
C
F
0.22µF
TO REMAINDER
OF SYSTEM
FROM INFET
Figure 7. Adjusting Input Current Limit
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 LTC4012
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
(A)
R
CL
VALUE (1%)
(Ω)
R
CL
POWER
DISSIPATION
(W)
R
CL
POWER
RATING
(W)
1.00 0.100 0.100 0.25
1.25 0.080 0.125 0.25
1.50 0.068 0.150 0.25
1.75 0.056 0.175 0.25
2.00 0.050 0.200 0.25
2.50 0.039 0.244 0.50
3.00 0.033 0.297 0.50
3.50 0.027 0.331 0.50
4.00 0.025 0.400 0.50
Figure 7 shows an optional circuit that can influence
the parameters of the input current limit in two ways.