Datasheet

OPA541
7
SBOS153A
www.ti.com
FIGURE 1. Safe Operating Area.
across the output transistor decreases and the device can
safely provide large output currents demanded by the load.
Short circuit protection requires evaluation of the SOA.
When the amplifier output is shorted to ground, the full
power supply voltage is impressed across the conducting
output transistor. The current limit must be set to a value
which is safe for the power supply voltage used. For in-
stance, with V
S
±35V, a short to ground would force 35V
across the conducting power transistor. A current limit of
1.8A would be safe.
Reactive, or EMF-generating, loads such as DC motors can
present difficult SOA requirements. With a purely reactive
load, output voltage and load current are 90° out of phase.
Thus, peak output current occurs when the output voltage is
zero and the voltage across the conducting transistor is equal
to the full power supply voltage. See Burr-Brown Applica-
tion Bulletin SBOA022 (available at www.ti.com) for fur-
ther information on evaluating SOA.
REPLACING HYBRID POWER AMPLIFIERS
The OPA541 can be used in applications currently using
various hybrid power amplifiers, including the OPA501,
OPA511, OPA512, and 3573. Of course, the application
must be evaluated to assure that the output capability and
other performance attributes of the OPA541 meet the neces-
sary requirements. These hybrid power amplifiers use two
current limit resistors to independently set the positive and
negative current limit value. Since the OPA541 uses only
one current limit resistor to set both the positive and negative
current limit, only one resistor (see Figure 4) need be
installed. If installed, the resistor connected to pin 2 (TO-3
package) is superfluous, but it does no harm.
Because one resistor carries the current previously carried
by two, the resistor may require a higher power rating.
Minor adjustments may be required in the resistor value to
achieve the same current limit value. Often, however, the
change in current limit value when changing models is small
compared to its variation over temperature. Many applica-
tions can use the same current limit resistor.
FIGURE 3. Replacing OPA501 with OPA541.
APPLICATIONS CIRCUITS
10
1
0.1
1 10 100
|V – V | (V)
SOUT
SAFE OPERATING AREA
|I | (A)
O
T = +25°C
T = +85°C
C
C
AP, AM
BM, SM
T
C
= +125°C
“M” Package only
FIGURE 2. Clamping Output for EMF-Generating Loads.
10µF
OPA541
0.1µF
0.1µF
10µF
–V
S
D
2
D
1
L
Inductive or
EMF-Generating
Load
+V
S
D – D : IN4003
12
OPA541
Ω0.1
Ω
100k
R
2
Ω10k
R
1
V
IN
20pF
L
Ω
OPA541
0.1
Slave
A = –R /R
= –10
V21
Master
Ω10k
20pF
FIGURE 4. Isolating Capacitive Loads.
OPA541
1
2
8
R
CL
Not Required
OPA501
1
2
8
R
CL
R
CL
+
–
Pin 2 is open on OPA541.