參數(shù)資料
型號(hào): LTC4012IUF#PBF
廠商: LINEAR TECHNOLOGY CORP
元件分類: 穩(wěn)壓器
英文描述: SWITCHING CONTROLLER, 633 kHz SWITCHING FREQ-MAX, PQCC20
封裝: 4 X 4 MM, 0.75 MM HEIGHT, LEAD FREE, PLASTIC, MO-220WGGD-1, QFN-20
文件頁數(shù): 10/28頁
文件大?。?/td> 381K
代理商: LTC4012IUF#PBF
LTC4012/
LTC4012-1/LTC4012-2
4012fa
applications inForMation
Programming LTC4012-1/LTC4012-2 Output Voltage
The LTC4012-1/LTC4012-2 feature precision internal bat-
teryvoltagefeedbackresistortapsconfiguredforcommon
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.
R
mV
I
CL
LIM
=
100
where ILIM is the desired maximum current draw from
theDC(adapter)input,includingadjustmentsfortolerance,
if any.
Figure 6. Programming Input Current Limit
2
1
RCL
CDC
CF 0.1F
CLP
LTC4012
CLN
RF
5.1k
4012 F06
10k
FROM DC
POWER
INPUT
TO
REMAINDER
OF SYSTEM
3 INFET
2
1
CLP
CLN
17
INTVDD
LTC4012
RCL
1%
R3 = R1
1%
R1
1%
Q2
2SC2412
RF
2.49k 1%
R2
Q1
IMX1
4012 F07
CF
0.22F
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 (0.1F) 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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