OPA549 loads separated from the amplifier by long cables). Typically, Typical Circuit

OPA549 circuit
As mentioned earlier, once a heat sink has been selected,
the complete design should be tested under worst-case load
and signal conditions to ensure proper thermal protection.
Any tendency to activate the thermal protection circuitry may
indicate inadequate heat sinking.
The tab of the 11-lead power ZIP package is electrically
connected to the negative supply, V–. It may be desirable to
isolate the tab of the 11-lead power ZIP package from its
mounting surface with a mica (or other film) insulator. For
lowest overall thermal resistance, it is best to isolate the
entire heat sink OPA549 structure from the mounting surface
rather than to use an insulator between the semiconductor
and heat sink.
avoided with clamp Diodes from the output terminal to the
power supplies, as shown in Figure 8. Schottky Rectifier
Diodes with a 8A or greater continuous rating are recom-
mended.
VOLTAGE SOURCE APPLICATION
Figure 9 illustrates how to use the OPA549 to provide an
accurate voltage source with only three external Resistors
First, the current limit Resistor R
CL
, is chosen according to
the desired output current. The resulting voltage at the I
LIM
pin is constant and stable over temperature. This voltage,
V
CL
, is connected to the noninverting input of the op amp and
used as a Voltage Reference thus eliminating the need for an
external reference. The feedback Resistors are selected to
gain V
CL
to the desired output voltage level.
OUTPUT STAGE COMPENSATION
The complex load impedances common in power op amp
applications can cause output stage instability. For normal
operation, output compensation circuitry is typically not re-
quired. However, for difficult loads or if the OPA549 is in-
tended to be driven into current limit, an R/C network may be
required. Figure 8 shows an output R/C compensation (snub-
ber) network which generally provides excellent stability.
R
1
R
2
V+
4.75V
V
O
= V
CL
(1 + R
2
/R
1
)
Ref
I
O
=
15800 (4.75V)
7500Ω + R
CL
V+
V
CL
7500Ω
R
1
5kΩ
V
IN
R
2
20kΩ
R
G = –
2
= –4
R
1
V–
I
LIM
D
1
OPA549
D
2
10Ω
(Carbon)
0.01µF
0.01µF
(Optional, for noisy
environments)
R
CL
Uses voltage developed at I
LIM
pin
as a moderately accurate reference
voltage.
For Example:
If I
LIM
= 7.9A, R
CL
= 2kΩ
V
CL
=
2kΩ • 4.75V
(2kΩ + 7500Ω)
= 1V
10
1
= 10
V–
D
1
, D
2
: Schottky Diodes
FIGURE 8. Motor Drive Circuit.
A snubber circuit may also enhance stability when driving
large capacitive loads (> 1000pF) or inductive loads (motors,
loads separated from the amplifier by long cables). Typically,
3Ω to 10Ω Resistors in series with 0.01µF to 0.1µF Capacitors
is adequate. Some variations in circuit values may be required
with certain loads.
Desired V
O
= 10V, G =
R
1
= 1kΩ and R
2
= 9kΩ
FIGURE 9. Voltage Source.
PROGRAMMABLE POWER SUPPLY
A programmable source/sink power supply can easily be
built using the OPA549. Both the output voltage and output
current are user-controlled. See Figure 10 for a circuit using
Potentiometers to adjust the output voltage and current while
Figure 11 uses DACs An LED connected to the E/S pin
through a logic Gate indicates if the OPA549 is in thermal
shutdown.
OUTPUT PROTECTION
Reactive and EMF-generating loads can return load current
to the amplifier, causing the output voltage to exceed the
power-supply voltage. This damaging condition can be
12
OPA549
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