APPLICATIONS INFORMATION
Figure 1 shows the OPA548 connected as a basic non-
inverting amplifier. The OPA548 can be used in virtually
any op amp configuration.
Power supply terminals should be bypassed with low series
impedance capacitors. The technique shown, using a ce-
ramic and tantalum type in parallel is recommended. In
addition, we recommend a 0.01µF capacitor between V+
and V– as close to the OPA548 as possible. Power supply
wiring should have low series impedance.
V+
10µF
+
0.1µF
(2)
R
1
5
2
7
6
With the OPA548, the simplest method for adjusting the
current limit uses a resistor or potentiometer connected
between the I
LIM
pin and V– according to the equation:
R
CL
=
(
15000
)(
4. 75
)
I
LIM
– 13750Ω
The low level control signal (0 to 330µA) also allows the
current limit to be digitally controlled.
Figure 3 shows a simplified schematic of the internal cir-
cuitry used to set the current limit. Leaving the I
LIM
pin open
programs the output current to zero, while connecting I
LIM
directly to V– programs the maximum output current limit,
typically 5A.
SAFE OPERATING AREA
Stress on the output transistors is determined both by the
output current and by the output voltage across the conduct-
ing output transistor, V
S
– V
O
. The power dissipated by the
output transistor is equal to the product of the output current
and the voltage across the conducting transistor, V
S
– V
O
.
The Safe Operating Area (SOA curve, Figure 2) shows the
permissible range of voltage and current.
G = 1+
R
2
R
1
R
2
E/S
V
O
Z
L
OPA548
3
4
V
IN
1
I
LIM(1)
0.1µF
(2)
0.01µF
(2)
10µF
+
SAFE OPERATING AREA
10
Current-Limited
Output Current (A)
V–
NOTE: (1) I
LIM
connected to V– gives the maximum current
limit, 5A (peak). (2) Connect capacitors directly to package
power supply pins.
PD
T
C
= 25°C
=5
0W
FIGURE 1. Basic Circuit Connections.
POWER SUPPLIES
The OPA548 operates from single (+8V to +60V) or dual
(±4V to
±30V)
supplies with excellent performance. Most
behavior remains unchanged throughout the full operating
voltage range. Parameters which vary significantly with
operating voltage are shown in the typical performance
curves.
Some applications do not require equal positive and negative
output voltage swing. Power supply voltages do not need to
be equal. The OPA548 can operate with as little as 8V
between the supplies and with up to 60V between the
supplies. For example, the positive supply could be set to
55V with the negative supply at –5V, or vice-versa.
ADJUSTABLE CURRENT LIMIT
The OPA548 features an accurate, user-selected current
limit. Current limit is set from 0 to 5A by controlling the
input to the I
LIM
pin. Unlike other designs which use a power
resistor in series with the output current path, the OPA548
senses the load indirectly. This allows the current limit to be
set with a 0 to 330µA control signal. In contrast, other
designs require a limiting resistor to handle the full output
current (5A in this case).
®
1
Output current can
be limited to less
than 3A—see text.
PD
PD
=1
=2
6W
0W
T
C
= 85°C
Pulse Operation Only
T = 125°C
(Limit rms current to
≤
3A)
C
1
2
5
10
20
50
100
V
S
–
V
O
(V)
0.1
FIGURE 2. Safe Operating Area.
The safe output current decreases as V
S
– V
O
increases. Out-
put short-circuits are a very demanding case for SOA. A
short-circuit to ground forces the full power supply voltage
(V+ or V–) across the conducting transistor. Increasing the
case temperature reduces the safe output current that can be
tolerated without activating the thermal shutdown circuit of
the OPA548. For further insight on SOA, consult Applica-
tion Bulletin AB-039.
AMPLIFIER MOUNTING
Figure 4 provides recommended solder footprints for both the
TO-220 and DDPAK power packages. The tab of both pack-
ages is electrically connected to the negative supply, V–. It
may be desirable to isolate the tab of TO-220 package from its
OPA548
8
BURR-BROWN [ BURR-BROWN CORPORATION ]
