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LT1806/LT1807

18067fc

or 8-lead MSOP package. All packages have the V – sup-

ply pin fused to the lead frame to enhance the thermal

conductance when connecting to a ground plane or a

large metal trace. Metal trace and plated through-holes

can be used to spread the heat generated by the device

to the backside of the PC board. For example, on a 3/32"

FR-4 board with 2oz copper, a total of 660 square mil-

limeters connects to Pin 4 of LT1807 in an SO-8 package

(330 square millimeters on each side of the PC board) will

bring the thermal resistance,

θJA,toabout85°C/W.Without

extra metal trace beside the power line connecting to the

V – pin to provide a heat sink, the thermal resistance will be

around 105°C/W. More information on thermal resistance

for all packages with various metal areas connecting to

the V – pin is provided in Tables 1, 2 and 3.

Table 1. LT1806 6-Lead SOT-23 Package

COPPER AREA

BOARD AREA

(mm2)

THERMAL RESISTANCE

(JUNCTION-TO-AMBIENT)

TOPSIDE (mm2)

270

2500

135°C/W

100

2500

145°C/W

2500

160°C/W

2500

200°C/W

Device is mounted on topside.

Table 2. LT1806/LT1807 SO-8 Package

COPPER AREA

BOARD AREA

(mm2)

THERMAL RESISTANCE

(JUNCTION-TO-AMBIENT)

TOPSIDE

(mm2)

BACKSIDE

(mm2)

1100

2500

65°C/W

330

2500

85°C/W

2500

95°C/W

2500

100°C/W

2500

105°C/W

Device is mounted on topside.

APPLICATIONS INFORMATION

Table 3. LT1807 8-Lead MSOP Package

COPPER AREA

BOARD AREA

(mm2)

THERMAL RESISTANCE

(JUNCTION-TO-AMBIENT)

TOPSIDE

(mm2)

BACKSIDE

(mm2)

540

2500

110°C/W

100

2500

120°C/W

100

2500

130°C/W

2500

135°C/W

2500

140°C/W

Device is mounted on topside.

Junction temperature TJ is calculated from the ambient

temperature TA and power dissipation PD as follows:

TJ = TA + (PD • θJA)

The power dissipation in the IC is the function of the supply

voltage, output voltage and the load resistance. For a given

supply voltage, the worst-case power dissipation PD(MAX)

occurs at the maximum quiescent supply current and at

the output voltage which is half of either supply voltage

(or the maximum swing if it is less than 1/2 the supply

voltage). PD(MAX) is given by:

PD(MAX) = (VS • IS(MAX)) + (VS/2)2/RL

Example: An LT1807 in SO-8 mounted on a 2500mm2

area of PC board without any extra heat spreading plane

connected to its V – pin has a thermal resistance of

105°C/W,

θJA. Operating on ±5V supplies with both ampli-

ﬁers simultaneously driving 50Ω loads, the worst-case

power dissipation is given by:

PD(MAX) = 2 • (10 • 14mA) + 2 • (2.5)2/50

= 0.28 + 0.25 = 0.53W

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