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參數(shù)資料
| 型號： | LTC4012IUF#TRPBF |
| 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)： | 8/28頁 |
| 文件大?。?/td> | 381K |
| 代理商： | LTC4012IUF#TRPBF |
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LTC4012/
LTC4012-1/LTC4012-2
4012fa
applications inForMation
Programming Charge Current
The formula for charge current is:
I
R
V
R
A
CHRG
IN
SENSE
PROG
=
.
– .
1 2085
11 67
The LTC4012 operates best with 3.01k input resistors,
although other resistors near this value can be used to
accommodate standard sense resistor values. Refer to
the subsequent discussion on inductor selection for other
considerations that come into play when selecting input
resistors RIN.
RSENSE should be chosen according to the following
equation:
R
mV
I
SENSE
MAX
=
100
where IMAX is the desired maximum charge current ICHRG.
The100mVtargetcanbeadjustedtosomedegreetoobtain
standard RSENSE values and/or a desired RPROG value, but
targetvoltageslowerthan100mVwillcauseaproportional
reduction in current regulation accuracy.
TherequiredminimumresistancebetweenPROGandGND
can be determined by applying the suggested expression
for RSENSE while solving the first equation given above for
charge current with ICHRG = IMAX:
R
V R
V
A R
PROG MIN
IN
(
)
.
.
=
+
1 2085
0 1
11 67
If RIN is chosen to be 3.01k with a sense voltage of 100mV,
this equation indicates a minimum value for RPROG of
26.9k. Table 6 gives some examples of recommended
charge current programming component values based
on these equations.
The resistance between PROG and GND can simply be
set with a single a resistor, if only maximum charge cur-
rent needs to be controlled during the desired charging
algorithm.
However, some batteries require a low charge cur-
rent for initial conditioning when they are heav-
ily discharged. The charge current can then be safely
switched to a higher level after conditioning is complete.
Figure 3 illustrates one method of doing this with 2-level
control of the PROG pin resistance. Turning Q1 off reduces
the charge current to IMAX/10 for battery conditioning.
When Q1 is on, the LTC4012 is programmed to allow
full IMAX current for bulk charge. This technique can be
expanded through the use of additional digital control
inputs for an arbitrary number of pre-programmed cur-
rent values.
For a truly continuous range of maximum charge current
control, pulse width modulation can be used as shown
in Figure 4.
Figure 3. Programming 2-Level Charge Current
13
Q1
2N7002
4012 F03
R2
53.6k
PROG
LTC4012
R1
26.7k
CPROG
4.7nF
BULK
CHARGE
PRECHARGE
Figure 4. Programming PWM Current
13
Q1
2N7002
4012 F04
PROG
LTC4012
RPROG
RMAX
511k
CPROG
0V
5V
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