1510 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'1510' PDF : 16 Pages View PDF
LT1510/LT1510-5
APPLICATIONS INFORMATION
BAT
INTERNAL
SENSE
RESISTOR
0.18Ω SENSE
LT1510
R1* C1
1.6k 0.1µF
GND
R2
D2
560k 1N4148
R3
430k
ADAPTER
OUTPUT 3.3V OR 5V
D1
1N4148
3–
8
7
LT1011
2+
4
1
R4
470k
NEGATIVE EDGE
TO TIMER
* TRIP CURRENT =
R1(VBAT)
(R2 + R3)(0.18Ω)
1510 F06
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 “top off” 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 (≈ 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°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° C/W thermal resistance) is about 0.8A for an 8.4V
battery and 1.1A for a 4.2V battery. This assumes a 60°C
maximum ambient temperature. The 16-pin SO, with a
thermal resistance of 50°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.
( )( ) ( ) PBIAS = 3.5mA VIN + 1.5mA VBAT
( ) [ ( )( )] 2
+ VBAT
VIN
7.5mA + 0.012 IBAT
( )( () ) PDRIVER =
IBAT
VBAT
2
1+
VBAT
30
55 VIN
( ) ( )( ) ( )( )( )( ) 2
PSW = IBAT
RSW
VIN
VBAT
+ tOL
VIN
IBAT
f
( )( )2
PSENSE = 0.18Ω IBAT
RSW = Switch ON resistance ≈ 0.35Ω
tOL = Effective switch overlap time ≈ 10ns
f = 200kHz (500kHz for LT1510-5)
12
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