Datasheet

DESIGN-IN TOOLS
DEMONSTRATION FIXTURES
MACROMODELS AND APPLICATIONS
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OUTPUT CURRENT AND VOLTAGE
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THERMAL ANALYSIS
BUF602
www.ti.com ...................................................................................................................................................... SBOS339B – OCTOBER 2005 – REVISED MAY 2008
BUF602 output drive capabilities, noting that the
graph is bounded by a Safe Operating Area of 1W
maximum internal power dissipation. Superimposing
resistor load lines onto the plot shows that the
BUF602 can drive ± 3V into 25 Ω or ± 3.5V into 50 Ω
Two printed circuit boards (PCBs) are available to
without exceeding the output capabilities or the 1W
assist in the initial evaluation of circuit performance
dissipation limit.
using the BUF602 in its two package options. Both of
these are offered free of charge as unpopulated
The minimum specified output voltage and current
PCBs, delivered with a user's guide. The summary
over-temperature are set by worst-case simulations at
information for these fixtures is shown in Table 1 .
the cold temperature extreme. Only at cold startup
will the output current and voltage decrease to the
Table 1. Demonstration Fixtures by Package
numbers shown in the Electrical Characteristic tables.
LITERATURE
As the output transistors deliver power, the junction
BOARD PART REQUEST
temperatures will increase, decreasing both V
BE
PRODUCT PACKAGE NUMBER NUMBER
(increasing the available output voltage swing) and
BUF602ID SO-8 DEM-BUF-SO-1A SBAU118
increasing the current gains (increasing the available
BUF602IDBV SOT23-5 DEM-BUF-SOT-1A SBAU117
output current). In steady-state operation, the
available output voltage and current will always be
The demonstration fixtures can be requested at the
greater than that shown in the over-temperature
Texas Instruments web site (www.ti.com ) through the
specifications, since the output stage junction
BUF602 product folder.
temperatures will be higher than the minimum
specified operating ambient.
For a buffer, the noise model is shown in Figure 35 .
SUPPORT
Equation 6 shows the general form for the output
Computer simulation of circuit performance using
noise voltage using the terms shown in Figure 35 .
SPICE is often useful when analyzing the
performance of analog circuits and systems. This is
particularly true for video and RF amplifier circuits
where parasitic capacitance and inductance can have
a major effect on circuit performance. A SPICE model
for the BUF602 is available through the TI web site
(www.ti.com ). These models do a good job of
predicting small-signal AC and transient performance
under a wide variety of operating conditions. They do
not do as well in predicting the harmonic distortion or
dG/dP characteristics. These models do not attempt
to distinguish between package types in their
small-signal AC performance.
Figure 35. Buffer Noise Analysis Model
The BUF602 provides output voltage and current
capabilities that are not usually found in wideband
buffers. Under no-load conditions at +25 ° C, the
output voltage typically swings closer than 1.2V to
either supply rail; the +25 ° C swing limit is within 1.2V
Due to the high output power capability of the
of either rail. Into a 15 Ω load (the minimum tested
BUF602, heatsinking or forced airflow may be
load), it is tested to deliver more than ± 60mA.
required under extreme operating conditions.
Maximum desired junction temperature will set the
The specifications described above, though familiar in
maximum allowed internal power dissipation as
the industry, consider voltage and current limits
described below. In no case should the maximum
separately. In many applications, it is the voltage ×
junction temperature be allowed to exceed 150 ° C.
current, or V-I product, which is more relevant to
circuit operation. Refer to the Buffer Output Voltage
Operating junction temperature (T
J
) is given by T
A
+
and Current Limitations plot (Figure 16 ) in the Typical
P
D
× θ
JA
. The total internal power dissipation (P
D
) is
Characteristics. The X and Y axes of this graph show
the sum of quiescent power (P
DQ
) and additional
the zero-voltage output current limit and the
power dissipated in the output stage (P
DL
) to deliver
zero-current output voltage limit, respectively. The
load power. Quiescent power is simply the specified
four quadrants give a more detailed view of the
no-load supply current times the total supply voltage
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