LT1510-5IGN datasheet(13/16 Pages) LINER

13 / 16 page

LT1510/LT1510-5

APPLICATIONS INFORMATION

Example: VIN = 15V, VBAT = 8.4V, IBAT = 1.2A;

PmA

BIAS

DRIVER

()( )+

()

+ ()

()( )

[]=

()( ) +









()

0012 12

017

12 84

55 15

013

kHz

SENSE

= () (

)( )







()( )(

)

()( ) =

−

035 8 4

10 10

15 1 2 200

028 0 04

032

018 1 2

0 26

•.

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,

DRIVER

BAT

()( )( ) +









()

For example, VX = 3.3V,

AVV

DRIVER =

()()() +









()

55 15

0 045

The average IVX required is:

DRIVER

0 045

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

BOARD AREA (IN

1510 F08

510

S16, MEASURED FROM AIR AMBIENT

TO DIE USING COPPER LANDS AS

SHOWN ON DATA SHEET

2-LAYER BOARD

4-LAYER BOARD

Figure 9. LT1510 Thermal Resistance

BOOST

SENSE

IVX

1510 F07

LT1510

µF

Figure 8

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