AD816
Normally, the AD816 will be soldered directly to a copper pad.
Figure 47 plots θJA against size of copper pad. This data pertains
to copper pads on both sides of G10 epoxy glass board connected
together with a grid of feedthroughs on 5 mm centers.
The AD816 is equipped with a thermal shutdown circuit. This
circuit ensures that the temperature of the AD816 die remains
below a safe level. In normal operation, the circuit shuts down
the AD816 at approximately 180°C and allows the circuit to
turn back on at approximately 140°C. This built-in hysteresis
means that a sustained thermal overload will cycle between
power-on and power-off conditions. The thermal cycling typi-
cally occurs at a rate of 1 ms to several seconds, depending on
the power dissipation and the thermal time constants of the
package and heat sinking. Figures 48 and 49 illustrate the ther-
mal shutdown operation after driving OUT1 to the + rail, and
OUT2 to the – rail, and then short-circuiting to ground each
output of the AD816. The AD816 will not be damaged by
momentary operation in this state, but the overload condition
should be removed.
This data shows that loads of 100 ohms or greater will usually
not require any more than this. This is a feature of the AD816’s
15-lead power SIP package.
An important component of θJA is the thermal resistance of the
package to heatsink. The data given is for a direct soldered
connection of package to copper pad. The use of heatsink
grease either with or without an insulating washer will increase
this number. Several options now exist for dry thermal connec-
tions. These are available from Bergquist as part # SP600-90.
Consult with the manufacturer of these products for details of
their application.
2
COPPER HEAT SINK AREA (TOP AND BOTTOM) – in
1
2
3
35
30
AD816AVR, AY (θ = 2؇C/W)
JC
25
20
Figure 48. OUT2 Shorted to Ground Through a 2 Ω
Resistor, Square Wave Is OUT1, RF = 1 kΩ, RG = 222 Ω
15
10
0
0.5k
1k
1.5k
2k
2.5k
2
COPPER HEAT SINK AREA (TOP AND BOTTOM) – mm
Figure 47. Power Package Thermal Resistance vs. Heat
Sink Area
Other Power Considerations
There are additional power considerations applicable to the
AD816. First, as with many current feedback amplifiers, there is an
increase in supply current when delivering a large peak-to-peak
voltage to a resistive load at high frequencies. This behavior is
affected by the load present at the amplifier’s output. Figure 12
summarizes the full power response capabilities of the AD816
driver. These curves apply to the differential driver applications
(right-hand side of Figure 52). In Figure 12, maximum continu-
ous peak-to-peak output voltage is plotted vs. frequency for
various resistive loads. Exceeding this value on a continuous
basis can damage the AD816.
Figure 49. OUT1 Shorted to Ground Through a 2 Ω
Resistor, Square Wave Is OUT2, RF = 1 kΩ, RG = 222 Ω
REV. B
–13–
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