LTC4012 datasheet(18/28 Pages) LINER

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LTC4012/

LTC4012-1/LTC4012-2

4012f

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

VBAT VOLTAGE

LTC4012-1

LTC4012-2

FVS1

FVS0

4.1V

4.2V

GND

8.2V

8.4V

GND

INTVDD

12.3V

12.6V

INTVDD

GND

16.4V

16.8V

INTVDD

Programming Input Current Limit

To set the input current limit ILIM, 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.

LIM

100

where ILIM is the desired maximum current draw from

theDC(adapter)input,includingadjustmentsfortolerance,

if any.

Figure 6. Programming Input Current Limit

RCL

CDC

CF 0.1μF

CLP

LTC4012

CLN

5.1k

4012 F06

10k

FROM DC

POWER

INPUT

REMAINDER

OF SYSTEM

3 INFET

CLP

CLN

INTVDD

LTC4012

RCL

R3 = R1

2SC2412

2.49k 1%

IMX1

4012 F07

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 RCL current limit programming values.

A lowpass ﬁlter formed by RF (5.1k) and CF (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 RCL Values

ADAPTER

RATING

(A)

RCL VALUE (1%)

(Ω)

RCL POWER

DISSIPATION

(W)

RCL POWER

RATING

(W)

1.00

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.

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