0.18鈩?/div>
INTERNAL
SENSE
RESISTOR
SENSE
3.3V OR 5V
LT1510
GND
R2
D2
560k 1N4148
R3
430k
Figure 7. Current Comparator for Initiating Float Time-Out
voltage decrease is detected as an indication of near full
charge. The charging current is then reduced to a much
lower value and maintained as a constant trickle charge.
An intermediate 鈥渢op off鈥?current may be used for a fixed
time period to reduce 100% 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 ap-
proached is not nearly as pronounced. This makes it more
difficult to use dV/dt as an indicator of full charge, and
change of temperature is more often used with a tempera-
ture sensor in the battery pack. Secondly, constant trickle
charge may not be recommended. Instead, a moderate
level of current is used on a pulse basis (鈮?1% to 5% duty
cycle) with the time-averaged value substituting for a
constant low trickle.
Thermal Calculations
If the LT1510 is used for charging currents above 0.4A, a
thermal calculation should be done to ensure that junction
temperature will not exceed 125擄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 charging current for the 8-pin SO package
(125擄 C/W thermal resistance) is about 0.8A for an 8.4V
12
U
W
U
U
D1
1N4148
鈥?/div>
+
1
8
7
4
R4
470k
NEGATIVE EDGE
TO TIMER
LT1011
2
* TRIP CURRENT =
R1(V
BAT
)
(R2 + R3)(0.18鈩?
1510 F06
battery and 1.1A for a 4.2V battery. This assumes a 60擄C
maximum ambient temperature. The 16-pin SO, with a
thermal resistance of 50擄C/W, can provide a full 1.5A
charging current in many situations. The 16-pin PDIP falls
between these extremes. Graphs are shown in the Typical
Performance Characteristics section.
P
BIAS
=
3
.
5mA V
IN
+
1
.
5mA V
BAT
2
BAT
( )( )
( )
(
V
)
7
.
5mA
+
(
0
.
012
)(
I
)
+
V
IN
[
BAT
]
P
DRIVER
P
SW
P
SENSE
(
I
)(
V
)
=
55
(
V
)
(
I
) (
R
)(
V
)
+
(
t
)(
V
)(
I
)(
f
)
=
V
=
(
0
.
18
鈩?/div>
)(
I
)
BAT
BAT
IN
2
BAT
SW
IN
BAT
OL
IN
BAT
2
BAT
2
錚?/div>
V
BAT
錚?/div>
錚?/div>
1
+
30
錚?/div>
錚?/div>
錚?/div>
R
SW
= Switch ON resistance
鈮?/div>
0.35鈩?/div>
t
OL
= Effective switch overlap time
鈮?/div>
10ns
f = 200kHz (500kHz for LT1510-5)
LT1510I相關(guān)型號PDF文件下載
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