10

Applications Information

Thermal Model

The steady state thermal model for the HSSR-7110 is

shown in Figure 21. The thermal resistance values given

in this model can be used to calculate the temperatures

at each node for a given operating condition. The thermal

resistances between the LED and other internal nodes

are very large in comparison with the other terms and

are omitted for simplicity. The components do, however,

interact indirectly through θCA, the case-to-ambient

which raises the case temperature TC accordingly. The val-

ue of θCA depends on the conditions of the board design

and is, therefore, determined by the designer.

The maximum value for each output MOSFET junction-

to-case thermal resistance is specified as 15°C/W . The

thermal resistance from FET driver junction-to-case is also

15°C/W/W. The power dissipation in the FET driver, how-

ever, is negligible in comparison to the MOSFETs.

On-Resistance and Rating Curves

is the resistance measured across the output contact

the output pins. The use of a pulsed signal (≤ 30 ms) im-

plies that each junction temperature is equal to the am-

bient and case temperatures. The steadystate resistance,

sured across the output contact when a DC current signal

is applied to the output pins for a duration sufficient to

temperature rise of each element in the thermal model.

Rating curves are shown in Figures 2 and 4. Figure 2 speci-

fies the maximum average output current allowable for a

given ambient temperature. Figure 4 specifies the output

power dissipation allowable for a given ambient tempera-

40°C/W/W), the maximum allowable output current and

power dissipation are related by the expression RSS =

ing within the safe area assures that the steady-state junc-

tion temperatures remain less than 150°C. As an example,

output current should be limited to less than 610 mA. A

check with Figure 4 shows that the output power dissipa-

than 0.35 W. This yields an RSS of 0.94 Ω.

Figure 20. Burn-In Circuit.

NOTE:

IN ORDER TO DETERMINE V

BE MEASURED FOR THE BURN-IN BOARDS TO BE USED. THEN, KNOWING

CORRECT OUTPUT CURRENT PER FIGURES 2 AND 4 TO INSURE THAT THE DEVICE MEETS THE

DERATING REQUIREMENTS AS SHOWN.

2

3

4

1

6

7

5

8

5.5 V

1.0

200

1.0

HSSR-7110

Figure 21. Thermal Model.

T je = LED JUNCTION TEMPERATURE

T jf1 = FET 1 JUNCTION TEMPERATURE

T jf2 = FET 2 JUNCTION TEMPERATURE

T jd = FET DRIVER JUNCTION TEMPERATURE

T C = CASE TEMPERATURE (MEASURED AT CENTER

OF PACKAGE BOTTOM)

T A = AMBIENT TEMPERATURE (MEASURED 6" AWAY

FROM THE PACKAGE)

CA = CASE-TO-AMBIENT THERMAL RESISTANCE

ALL THERMAL RESISTANCE VALUES ARE IN ˚C/W

T je

CA

104

15

T A

T C

T jd

T jf1

15

15

T jf2

V OS

+

DIGITAL

NANOVOLTMETER

ISOTHERMAL CHAMBER

HSSR-7110

2

3

4

1

6

7

5

8

-

IF

+

-

Figure 19. Voltage Offset Test Setup.