Datasheet

OPA549
SBOS093E
8
www.ti.com
APPLICATIONS INFORMATION
Figure 1 shows the OPA549 connected as a basic noninverting
amplifier. The OPA549 can be used in virtually any op amp
configuration.
Power-supply terminals should be bypassed with low series
impedance capacitors. The technique shown in Figure 1, using
a ceramic and tantalum type in parallel, is recommended.
Power-supply wiring should have low series impedance.
Be sure to connect both output pins (pins 1 and 2).
CONTROL REFERENCE (Ref) PIN
The OPA549 features a reference (Ref) pin to which the I
LIM
and the E/S pin are referred. Ref simply provides a reference
point accessible to the user that can be set to V–, ground, or
any reference of the user’s choice. Ref cannot be set below
the negative supply or above (V+) – 8V. If the minimum V
S
is used, Ref must be set at V–.
ADJUSTABLE CURRENT LIMIT
The OPA549’s accurate, user-defined current limit can be set
from 0A to 10A 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 OPA549 senses the load indirectly.
This allows the current limit to be set with a 0µA to 633µA
control signal. In contrast, other designs require a limiting
resistor to handle the full output current (up to 10A in this
case).
Although the design of the OPA549 allows output currents up
to 10A, it is not recommended that the device be operated
continuously at that level. The highest rated continuous
current capability is 8A. Continuously running the OPA549 at
output currents greater than 8A will degrade long-term reli-
ability.
Operation of the OPA549 with current limit less than 1A
results in reduced current limit accuracy. Applications requir-
ing lower output current may be better suited to the OPA547
or OPA548.
Resistor-Controlled Current Limit
See Figure 2a for a simplified schematic of the internal
circuitry used to set the current limit. Leaving the I
LIM
pin open
programs the output current to zero, while connecting I
LIM
directly to Ref programs the maximum output current limit,
typically 10A.
With the OPA549, the simplest method for adjusting the
current limit uses a resistor or potentiometer connected
between the I
LIM
pin and Ref according to Equation 1:
R
75kV
I
– 7.5k
CL
LIM
=Ω
(1)
Refer to Figure 2 for commonly used values.
Digitally-Controlled Current Limit
The low-level control signal (0µA to 633µA) also allows the
current limit to be digitally controlled by setting either a
current (I
SET
) or voltage (V
SET
). The output current I
LIM
can be
adjusted by varying I
SET
according to Equation 2:
I
SET
= I
LIM
/15800 (2)
Figure 2b demonstrates a circuit configuration implementing
this feature.
The output current I
LIM
can be adjusted by varying V
SET
according to Equation 3:
V
SET
= (Ref) + 4.75V – (7500W)(I
LIM
)/15800 (3)
Figure 11 demonstrates a circuit configuration implementing
this feature.
FIGURE 1. Basic Circuit Connections.
POWER SUPPLIES
The OPA549 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 that vary significantly with operat-
ing voltage are shown in the Typical Characteristics. Some
applications do not require equal positive and negative out-
put voltage swing. Power-supply voltages do not need to be
equal. The OPA549 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. Be sure to connect both V– pins
(pins 5 and 7) to the negative power supply, and both V+
pins (pins 10 and 11) to the positive power supply.
Package tab is internally connected to V–; however, do
not use the tab to conduct current.
G = 1+
R
2
R
1
Z
L
E/S
8
9
10, 11
3
4
5, 7
6
1, 2
R
2
I
LIM
(1)
Ref
R
1
0.1µF
(2)
10µF
OPA549
V–
V+
+
+
V
IN
10µF
0.1µF
(2)
V
O
NOTES: (1) I
LIM
connected to Ref gives the maximum
current limit, 10A (peak). (2) Connect capacitors directly to
package power-supply pins.