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参数资料
| 型号： | LTC4012IUF-2#PBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING CONTROLLER, 633 kHz SWITCHING FREQ-MAX, PQCC20 |
| 封装： | 4 X 4 MM, 0.75 MM HEIGHT, LEAD FREE, PLASTIC, MO-220WGGD-1, QFN-20 |
| 文件页数： | 9/28页 |
| 文件大小： | 381K |
| 代理商： | LTC4012IUF-2#PBF |
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4012fa
LTC4012/
LTC4012-1/LTC4012-2
applications inForMation
The value of RPROG controls the maximum value of charge
current which can be programmed (Q1 continuously on).
PWM of the Q1 gate voltage changes the value of RPROG
to produce lower currents. The frequency of this modula-
tion should be higher than a few kHz, and CPROG must be
increased to reduce the ripple caused by switching Q1. In
addition, it may be necessary to increase loop compensa-
tion capacitance connected to ITH to maintain stability or
prevent large current overshoot during start-up. Selecting
a higher Q1 PWM frequency (≈10kHz) will reduce the need
to change CPROG or other compensation values. Charge
current will be proportional to the duty cycle of the PWM
input on the gate of Q1.
Programming LTC4012 Output Voltage
Figure 5 shows the external circuit for programming the
charger voltage when using the LTC4012. The voltage is
then governed by the following equation:
V
V R R
R
R A R B
BAT =
+
(
)
=
+
1 2085
1
2
.
,
See Table 2 for approximate resistor values for R2.
R R
V
R
R A R B
1
2
1 2085
1
2
=
=
+
VBAT
.
– ,
Selecting R2 to be less than 50k and the sum of R1 and
R2 at least 200k or above, achieves the lowest possible
error at the VFB sense input. Note that sources of error
such as R1 and R2 tolerance, FBDIV RON or VFB input
impedance are not included in the specifications given in
the Electrical Characteristics. This leads to the possibil-
ity that very accurate (0.1%) external resistors might be
required. Actually, the temperature rise of the LTC4012 will
rarely exceed 50°C at the end of charge, because charge
current will have tapered to a low level. This means that
0.25% resistors will normally provide the required level of
overall accuracy. Table 2 gives recommended values for
R1 and R2 for popular lithium-ion battery voltages. For
values of R1 above 200k, addition of capacitor CZ may
improve transient response and loop stability. A value of
10pF is normally adequate.
Table 2. Programming Output Voltage
VBAT
(V)
R1 (0.25%)
(kΩ)
R2A (0.25%)
(kΩ)
R2B (1%)*
(Ω)
4.1
165
69
–
4.2
167
67.3
200
8.2
162
28
–
8.4
169
28.4
–
12.3
301
32.8
–
12.6
294
31.2
–
16.4
284
22.6
–
16.8
271
21
–
20.5
316
19.8
–
21
298
18.2
–
24.6
298
15.4
–
25.2
397
20
–
*To Obtain Desired Accuracy Requires Series Resistors For R2.
Figure 5. Programming Output Voltage
11
10
BAT
FBDIV
85
TYPICAL
9
VFB
LTC4012
R1
R2A
R2B*
4012 F05
CZ
21
GND
(EXPOSED PAD)
*OPTIONAL TRIM RESISTOR
+
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