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參數(shù)資料
| 型號： | LTC1734 |
| 廠商： | Linear Technology Corporation |
| 英文描述： | Lithium-Ion Linear Battery Charger in SOT-23(鋰離子線性電池充電器（SOT-23封裝）) |
| 中文描述： | 鋰離子線性電池充電器采用SOT - 23（鋰離子線性電池充電器（采用SOT - 23封裝）） |
| 文件頁數(shù)： | 7/8頁 |
| 文件大?。?/td> | 140K |
| 代理商： | LTC1734 |
7
LTC1734
APPLICATIO
S I
FOR
ATIO
U
For example, to program a charge current of 500mA with
a minimum supply voltage of 4.75V, the minimum operat-
ing V
CE
is:
V
CE(MIN)
(V) = 4.75 – (0.5)(0.1) – 4.2 = 0.5V
The actual battery charge current (I
BAT
) is slightly smaller
than the expected charge current because the charger
senses the emitter current and the battery charge current
will be reduced by the base current. In terms of
β
(I
C
/I
B
),
I
BAT
can be calculated as follows:
I
BAT
(A) = 1000 I
PROG
[
β
/(
β
+ 1)]
If
β
= 50, then I
BAT
is 2% low.
If desired, the 2% loss can
be compensated for by increasing I
PROG
by 2%.
Another important factor to consider when choosing the
PNP pass transistor is the power handling capability. The
PNP’s data sheet will usually give the maximum rated
power dissipation at a given ambient temperature with a
power derating for elevated temperature operation. The
maximum power dissipation of the PNP when charging is:
P
D(MAX)
(W) = I
BAT
(V
DD(MAX)
– V
BAT(MIN)
)
V
DD(MAX)
is the maximum supply voltage and V
BAT(MIN)
is
the minimum battery voltage when discharged.
W
U
U
(>300) and very low ESR output capacitors (especially
ceramic) reduces the phase margin, possibly resulting in
oscillation. Adding series resistance to the capacitor will
restore the phase margin. The last transistor listed in each
row of Table 1 is high beta.
In the constant current mode it is the PROG pin that is in
the feedback loop and not the battery. Because the PROG
pin is in a closed-loop signal path, the pole frequency
should be kept above 400kHz to maintain adequate AC
stability. In addition, high loop gains should be avoided by
limiting R
PROG
to 15k or less. The pole frequency is
determined by R
PROG
and the external capacitive loading
on the PROG pin. Once R
PROG
is determined, the maxi-
mum value of C which will give adequate stability can be
calculated as follows:
C
MAX
(F) = 1/(6.28 R
PROG
400k)
A capacitance of 25pF or less is acceptable for any R
PROG
value.
To minimize capacitive loading of the PROG pin, a 10k
resistor can be added between the PROG pin and the
monitoring circuit to allow the charger to be unaffected by
the capacitance.
V
CC
Bypass Capacitor
Many types of capacitors with values ranging from 1
μ
F to
10
μ
F located close to the LTC1734 will provide adequate
input bypassing. However, caution must be exercised
when using multilayer ceramic capacitors. Because of the
self resonant and high Q characteristics of some types of
ceramic capacitors, high voltage transients can be gener-
ated under some start-up conditions, such as connecting
the charger input to a hot power source. To prevent these
transients from exceeding the absolute maximum voltage
rating, several ohms can be added in series with the input
ceramic capacitor.
Internal Protection
Internal protection is provided to prevent excessive DRIVE
currents (I
DSHRT
) and excessive internal self-heating in
case of a fault condition, such as a shorted DRIVE pin or
the external PNP pass transistor operating in deep
saturation.
Table 1. Recommended Low V
CESAT
PNP Transistors
Maximum
Maximum P
D
at
Current (A)
T
A
= 25
°
C
1
0.5
1
1
2
2
Package
Style
SOT-23
SOT-89
SOT-223
Zetex Part Number
FMMT549 or FMMT717
FCX589 or FCX717
FZT549 or BCP69
Stability
The LTC1734 contains two control loops; constant voltage
and constant current. To maintain adequate AC stability in
the constant voltage mode, a capacitance (5
μ
F to 100
μ
F)
is required from the BAT pin to ground. A battery and the
interconnecting wires can appear inductive at high fre-
quencies, and since the battery is in the feedback loop, this
capacitance is necessary to compensate for the induc-
tance. The capacitor ESR can range from near zero ohms
to several ohms.
In general, compensation is optimal with 4.7
μ
F to 22
μ
F
and ESR of 0.5
to 1.5
. Using high beta PNP transistors
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| LTC1734ES6-4.1#TRM | 功能描述:IC BATT CHRGR LI-ION LIN SOT23-6 RoHS:否 類別:集成電路 (IC) >> PMIC - 電池管理 系列:- 標(biāo)準(zhǔn)包裝:61 系列:- 功能:電源管理 電池化學(xué):鋰離子（Li-Ion）、鋰聚合物（Li-Pol） 電源電壓:4.35 V ~ 5.5 V 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:22-WFDFN 裸露焊盤 供應(yīng)商設(shè)備封裝:22-DFN（6x3）裸露焊盤 包裝:管件 |
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