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參數(shù)資料
| 型號(hào)： | LT1513 |
| 廠商： | Linear Technology Corporation |
| 英文描述： | SEPIC Constant- or Programmable-Current/ Constant-Voltage Battery Charger(初級(jí)線圈感應(yīng)轉(zhuǎn)換，恒定電流或可編程電流/恒定電壓電池充電器) |
| 中文描述： | SEPIC拓?fù)涞暮愣ɑ蚩删幊屉娏?恒定電壓電池充電器（初級(jí)線圈感應(yīng)轉(zhuǎn)換，恒定電流或可編程電流/恒定電壓電池充電器） |
| 文件頁數(shù)： | 7/16頁 |
| 文件大?。?/td> | 258K |
| 代理商： | LT1513 |
7
LT1513/LT1513-2
APPLICATIO
S I
N
FOR
ATIO
U
The LT1513 is an IC battery charger chip specifically opti-
mized to use the SEPIC converter topology. A complete
charger schematic is shown in Figure 1. The SEPIC topology
has unique advantages for battery charging. It will operate
with input voltages above, equal to or below the battery
voltage, has no path for battery discharge when turned off,
and eliminates the snubber losses of flyback designs. It also
has a current sense point that is ground referred and need
not be connected directly to the battery. The two inductors
shown are actually just two identical windings on one
inductor core, although two separate inductors can be used.
A current sense voltage is generated with respect to ground
across R3 in Figure 1. The average current through R3 is
always identical to the current delivered to the battery. The
LT1513 current limit loop will servo the voltage across R3
to –100mV when the battery voltage is below the voltage
limit set by the output divider R1/R2. Constant-current
charging is therefore set at 100mV/R3. R4 and C4 filter the
current signal to deliver a smooth feedback voltage to the I
FB
pin. R1 and R2 form a divider for battery voltage sensing and
set the battery float voltage. The suggested value for R2 is
12.4k. R1 is calculated from:
R V
R
A
1 245
20 3
+
μ
.
( .
)
V
BAT
= battery float voltage
0.3
μ
A = typical FB pin bias current
A value of 12.4k for R2 sets divider current at 100
μ
A. This is
a constant drain on the battery when power to the charger is
off. If this drain is too high, R2 can be increased to 41.2k,
reducing divider current to 30
μ
A. This introduces an addi-
tional uncorrectable error to the constant voltage float mode
of about
±
0.5% as calculated by:
W
U
R
BAT
1
2
–1 245
=
(
)
V
Error =
0.15 A(R1)(R2)
1.245(R1+R2)
BAT
±
±
0.15
μ
A = expected variation in FB bias current around the
nominal 0.3
μ
A typical value.
With R2 = 41.2k and R1 = 228k, (V
BAT
= 8.2V), the error due
to variations in bias current would be
±
0.42%.
A second option is to disconnect the divider when charger
power is off. This can be done with a small NFET as shown in
Figure 3. D2, C6 and R6 form a peak detector to drive the gate
of the FET to about the same as the battery voltage. If power
is turned off, the gate will drop to 0V and the only drain on the
battery will be the reverse leakage of the catch diode D1. See
Diode Selection for a discussion of diode leakage.
LT1513
V
IN
L1A
L1B
GND
V
FB
1513 F03
V
SW
ADAPTER
INPUT
C2
SCHEMATIC SIMPLIFIED FOR CLARITY
D2 = 1N914, 1N4148 OR EQUIVALENT
C6
470pF
R6
470k
R3
R1
R2
D2
D1
C1
+
Figure 3. Eliminating Divider Current
Maximum Input Voltage
Maximum input voltage for the LT1513 is partly determined
by battery voltage. A SEPIC converter has a maximum
switch voltage equal to input voltage plus output voltage.
The LT1513 has a maximum input voltage of 30V and a
maximum switch voltage of 40V, so this limits maximum
input voltage to 30V, or 40V – V
BAT
, whichever is less.
Shutdown and Synchronization
The dual function S/S pin provides easy shutdown and
synchronization. It is logic level compatible and can be
pulled high or left floating for normal operation. A logic low
on the S/S pin activates shutdown, reducing input supply
current to 12
μ
A. To synchronize switching, drive the S/S pin
between 600kHz and 800kHz.
Inductor Selection
L1A and L1B are normally just two identical windings on one
core, although two separate inductors can be used. A typical
value is 10
μ
H, which gives about 0.5A peak-to-peak induc-
tor current. Lower values will give higher ripple current,
which reduces maximum charging current. 5
μ
H can be used
if charging currents are at least 20% lower than the values
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| LT1521-3 | Cap-Free, NMOS, 150mA Low Dropout Regulator with Reverse Current Protection |
| LT1521-3.3 | Paired Cable; Jacket Material:Polyvinylchloride (PVC); Leaded Process Compatible:Yes RoHS Compliant: Yes |
| LT1521IST-3.3 | Cap-Free, NMOS, 150mA Low Dropout Regulator with Reverse Current Protection |
| LT1521IST-5 | Cap-Free, NMOS, 150mA Low Dropout Regulator with Reverse Current Protection |
| LT1521-5 | Cap-Free, NMOS, 150mA Low Dropout Regulator with Reverse Current Protection |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LT-1513-110-012 | 制造商:Carling Technologies 功能描述:LT-SERIES TOGGLE SWITCH - Bulk |
| LT-1513-110-125 | 制造商:Carling Technologies 功能描述:LT-SERIES TOGGLE SWITCH - Bulk |
| LT-1513-151-012 | 制造商:Carling Technologies 功能描述:LT-SERIES TOGGLE SWITCH - Bulk |
| LT1513-2 | 制造商:LINER 制造商全稱:Linear Technology 功能描述:SEPIC Constant- or Programmable-Current/ Constant-Voltage Battery Charger |
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