CONTROL REFERENCE (Ref) PIN
APPLICATIONS INFORMATION
Figure 1 shows the OPA549 connected as a basic non-
inverting amplifier. The OPA549 can be used in virtually
any op amp configuration.
The OPA549 features a reference (ref) pin to which the ILIM
and the Enable/Status (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 VS is used, Ref must be set at V–.
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. Power
supply wiring should have low series impedance.
ADJUSTABLE CURRENT LIMIT
Be sure to connect both output pins (pins 1 and 2).
The OPA549’s accurate, user-defined current limit can be
set from 0A to 10A by controlling the input to the ILIM 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).
V+
10µF
+
0.1µF(2)
R2
R1
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
reliability.
10, 11
E/S
9
3
1, 2
VO
OPA549
8
ZL
VIN
Ref
(1)
ILIM
4
6
R2
R1
5, 7
G = 1+
Operation of the OPA549 with current limit less than 1A
results in reduced current limit accuracy. Applications re-
quiring lower output current may be better suited to the
OPA547 or OPA548.
0.1µF(2)
10µF
Resistor-Controlled Current Limit
+
Figure 2a shows a simplified schematic of the internal
circuitry used to set the current limit. Leaving the ILIM pin
open programs the output current to zero, while connecting
ILIM directly to Ref programs the maximum output current
limit, typically 10A.
V–
NOTE: (1) ILIM connected to Ref gives the maximum
current limit, 10A (peak). (2) Connect capacitors directly to
package power supply pins.
With the OPA549, the simplest method for adjusting the
current limit uses a resistor or potentiometer connected
between the ILIM pin and Ref according to Equation 1:
FIGURE 1. Basic Circuit Connections.
75kV
RCL
=
– 7.5kΩ
(1)
ILIM
POWER SUPPLIES
Commonly used values are shown in Figure 2.
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 oper-
ating 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 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–, how-
ever, do use the tab to conduct current.
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(ISET)orvoltage(VSET). TheoutputcurrentILIMcanbe
adjusted by varying ISET according to Equation 2:
(2)
ISET = ILIM/15800
Figure 2b demonstrates a circuit configuration implement-
ing this feature.
The output current ILIM can be adjusted by varying VSET
according to Equation 3:
VSET = (Ref) + 4.75V – (7500Ω)(ILIM)/15800 (3)
Figure 11 demonstrates a circuit configuration implement-
ing this feature.
®
OPA549
8
BB [ BURR-BROWN CORPORATION ]
