LTC4012-2 Linear Technology Corporation, LTC4012-2 Datasheet - Page 18

• Manufacturer Part Number: LTC4012-2
• Description: Multi-Chemistry Battery Charger
• Manufacturer: Linear Technology Corporation

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LTC4012/
LTC4012-1/LTC4012-2
Programming LTC4012-1/LTC4012-2 Output Voltage
The LTC4012-1/LTC4012-2 feature precision internal bat-
tery voltage feedback resistor taps confi gured 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
Programming Input Current Limit
To set the input current limit I
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.
where I
the DC (adapter) input, including adjustments for tolerance,
if any.
18
APPLICATIONS INFORMATION
FROM DC
POWER
R
INPUT
LTC4012-1
CL
12.3V
16.4V
4.1V
8.2V
=
LIM
V
Figure 6. Programming Input Current Limit
BAT
100
I
is the desired maximum current draw from
LIM
VOLTAGE
C
DC
mV
10k
LTC4012-2
12.6V
16.8V
4.2V
8.4V
3 INFET
CLP
2
C
LTC4012
F
R
0.1μF
CL
CLN
INTV
INTV
1
LIM
FVS1
GND
GND
R
5.1k
F
, the minimum wall
DD
DD
4012 F06
TO
REMAINDER
OF SYSTEM
INTV
INTV
FVS0
GND
GND
DD
DD
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
A lowpass fi lter formed by R
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
Figure 7 shows an optional circuit that can infl uence
the parameters of the input current limit in two ways.
ADAPTER
RATING
1.00
1.25
1.50
1.75
2.00
2.50
3.00
3.50
4.00
(A)
LTC4012
INTV
Figure 7. Adjusting Input Current Limit
CLN
CLP
DD
R
CL
17
CL
2
1
CL
VALUE (1%)
0.100
0.080
0.068
0.056
0.050
0.039
0.033
0.027
0.025
Values
(Ω)
current limit programming values.
C
0.22μF
2.49k 1%
F
R1
1%
IMX1
R
R2
Q1
FROM INFET
F
F
DISSIPATION
R
(5.1k) and C
CL
R
1%
CL
0.100
0.125
0.150
0.175
0.200
0.244
0.297
0.331
0.400
(W)
POWER
TO REMAINDER
OF SYSTEM
Q2
2SC2412
R3 = R1
1%
R
4012 F07
F
CL
RATING
(0.1μF) is
0.25
0.25
0.25
0.25
0.25
0.50
0.50
0.50
0.50
POWER
(W)
4012f