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参数资料
| 型号： | LT1571-5 |
| 厂商： | Linear Technology Corporation |
| 英文描述： | Constant-Current/ Constant-Voltage Battery Charger with Preset Voltage and Termination Flag |
| 中文描述： | 恒流/恒压电池充电器预置电压和终止旗 |
| 文件页数： | 11/16页 |
| 文件大小： | 201K |
| 代理商： | LT1571-5 |
11
LT1571 Series
lower value and maintained as a constant trickle charge.
An intermediate “top off” current may also be used for a
fixed time period to reduce total charge time.
NiMH batteries are similar in chemistry to NiCd but have
two differences related to charging. First, the inflection
characteristic in battery voltage as full charge is
approached is not nearly as pronounced. This makes it
more difficult to use –dV/dt as an indicator of full charge,
and an increase in temperature is more often used with a
temperature sensor located in the battery pack. Secondly,
constant trickle charge may not be recommended. In-
stead, a moderate level of current is used on a pulse basis
(
≈
1% to 5% duty cycle) with the time-averaged value
substituting for a constant low trickle.
Thermal Calculations
If the LT1571 is used for charge currents above 0.4A, a
thermal calculation should be done to ensure that junction
temperature will not exceed 125
°
C. Power dissipation in
the IC is caused by bias and driver current, switch resis-
tance, switch transition losses and the current sense
resistor. The following equations show that maximum
practical charge current for the 16-pin SSOP package
(75
°
C/W thermal resistance) is about 1.2A for an 8.4V
battery and 1.4A for a 4.2V battery. This assumes a 60
°
C
maximum ambient temperature. The 28-pin SSOP, with a
thermal resistance of 40
°
C/W, can provide a full 1.5A
charge current in many situations.
P
mA V
)
mA V
V
V
(
mA
I
P
I
V
V
V
P
I
R
V
V
t
V
I
f
P
BIAS
IN
BAT
BAT
IN
BAT
DRIVER
BAT
BAT
BAT
30
IN
SW
BAT
SW
BAT
IN
)(
OL
IN
BAT
SENSE
=
(
+
(
)
+
)
+
(
)(
)
[
]
=
)(
)
(
+
)
)
+
(
=
(
) (
)(
)(
)(
)( )
=
3 5
.
1 5
.
7 5
.
0 012
.
1
55
0
2
2
2
.18
2
(
)
I
BAT
R
SW
= Switch ON resistance
≈
0.35
t
OL
= Effective switch overlap time
≈
10ns
f = 200kHz (500kHz for LT1571-5)
Example: V
IN
= 15V, V
BAT
= 8.4V, I
BAT
= 1.2A;
P
mA V
)
mA V
V
V
(
mA
I
P
I
V
V
V
P
I
R
V
V
t
V
I
f
P
BIAS
IN
BAT
BAT
IN
BAT
DRIVER
BAT
BAT
BAT
30
IN
SW
BAT
SW
BAT
IN
)(
OL
IN
BAT
SENSE
=
(
+
(
)
+
)
+
(
)(
)
[
]
=
)(
)
(
+
)
)
+
(
=
(
) (
)(
)(
)(
)( )
=
3 5
.
1 5
.
7 5
.
0 012
.
1
55
0
2
2
2
.18
2
(
)
I
BAT
Total power in the IC is:
0.17 + 0.13 + 0.32+ 0.26 = 0.88W
Temperature rise will be (0.88W)(40
°
C/W) = 35
°
C. This
assumes that the LT1571 is properly heat sunk by con-
necting all fused ground pins to the expanded traces and
that the PC board has a backside or internal plane for heat
spreading.
The P
DRIVER
term can be reduced by connecting the boost
diode D2 to a lower system voltage (lower than V
BAT
)
Figure 7. Charging NiMH or NiCd Batteries with
Constant Current (Efficiency at 0.5A
≈
90%)
SW
BOOST
GND
SENSE
V
CC
PROG
V
C
BAT
R2
11k
+
R1
100k
Q1
VN2222
V
(WALL ADAPTER)
* TOKIN OR MARCON CERAMIC
SURFACE MOUNT
** COILTRONICS CTX33-2
1571 F07
C1
0.22
μ
F
C
IN
*
10
μ
F
L1**
33
μ
H
LT1571-1
D1
1N5819
D3
1N5819
D2
1N914
C
OUT
22
F
TANT
0.1
μ
F
1k
1
μ
F
300
2V TO
20V
I
BAT
ON: I
BAT
= 0.5A
OFF: I
BAT
= 0.05A
+
APPLICATIOU
W
U
U
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| LT-1571-511-012 | 制造商:Carling Technologies 功能描述:LT-SERIES TOGGLE SWITCH - Bulk |
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| LT-1571-531-012 | 制造商:Carling Technologies 功能描述:LT-SERIES TOGGLE SWITCH - Bulk |
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