LT1510IS8 データシートの表示（PDF） - Linear Technology
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LT1510IS8 Datasheet PDF : 16 Pages
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LT1510/LT1510-5
APPLICATIONS INFORMATION
Example: VIN = 15V, VBAT = 8.4V, IBAT = 1.2A;
( )( ) ( ) PBIAS = 3.5mA 15 + 1.5mA 8.4
( ) [ ( )( )] 2
8.4
+
7.5mA + 0.012 1.2 = 0.17W
15
( )( )( ) PDRIVER =
1.2
8.4
2
1+
8.4
30
55 15
= 0.13W
(1.2)2(0.35)(8.4)
PSW =
15
+
( )( )( ) 10
•
10−9
15
1. 2
200kHz
= 0.28 + 0.04 = 0.32W
( )( )2
PSENSE = 0.18 1.2 = 0.26W
Total power in the IC is:
0.17 + 0.13 + 0.32+ 0.26 = 0.88W
Temperature rise will be (0.88W)(50°C/W) = 44°C. This
assumes that the LT1510 is properly heat sunk by con-
necting the four fused ground pins to the expanded traces
and that the PC board has a backside or internal plane for
heat spreading.
The PDRIVER term can be reduced by connecting the boost
diode D2 (see Figures 2 and 6 circuits) to a lower system
voltage (lower than VBAT) instead of VBAT (see Figure 8).
Then,
( )( )(( )) PDRIVER =
IBAT
VBAT
VX
1+
VX
30
55 VIN
For example, VX = 3.3V,
( )( )(( )) PDRIVER =
1.2A
8.4V
3.3V
1+
3.3V
30
55 15V
= 0.045W
The average IVX required is:
PDRIVER = 0.045W = 14mA
VX
3.3V
Total board area becomes an important factor when the
area of the board drops below about 20 square inches. The
graph in Figure 9 shows thermal resistance vs board area
for 2-layer and 4-layer boards. Note that 4-layer boards
have significantly lower thermal resistance, but both types
show a rapid increase for reduced board areas. Figure 10
shows actual measured lead temperature for chargers
operating at full current. Battery voltage and input voltage
will affect device power dissipation, so the data sheet
power calculations must be used to extrapolate these
readings to other situations.
Vias should be used to connect board layers together.
Planes under the charger area can be cut away from the
rest of the board and connected with vias to form both a
C1
L1
D2
VX
IVX
+
10µF
SW
LT1510
BOOST
SENSE
1510 F07
Figure 8
60
55
50
2-LAYER BOARD
45
40
4-LAYER BOARD
35
S16, MEASURED FROM AIR AMBIENT
30 TO DIE USING COPPER LANDS AS
SHOWN ON DATA SHEET
25
05
10 15 20 25 30 35
BOARD AREA (IN2)
1510 F08
Figure 9. LT1510 Thermal Resistance
13
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