CURRENT LIMIT
APPLICATIONS INFORMATION
The OPA551 and OPA552 are designed with internal cur-
rent-limiting circuitry that limits the output current to ap-
proximately 380mA. The current limit varies with increasing
junction temperature as shown in the typical curve “Current
Limit vs Temperature.” This, in combination with the ther-
mal protection circuitry, provides protection from many
types of overload conditions including short circuit to ground.
Figure 1 shows the OPA551 connected as a basic non-
inverting amplifier. The OPA551 can be used in virtually
any op amp configuration. OPA552 is designed for use in
configurations with gains of 5 or greater. Power supply
terminals should be bypassed with 0.1µF capacitors, or
greater, near the power supply pins. Be sure that the capaci-
tors are appropriately rated for the power supply voltage
used. The OPA551 and OPA552 can supply output currents
up to 200mA with excellent performance.
THERMAL PROTECTION
The OPA551 and OPA552 have thermal shutdown circuitry
that protects the amplifier from damage caused by overload
conditions. The thermal protection circuitry disables the
output when the junction temperature reaches approximately
160°C, allowing the device to cool. When the junction
temperature cools to approximately 140°C, the output cir-
cuitry is automatically re-enabled.
V+
10µF
R2
G = 1+
+
R1
0.1µF
R2
R1
The thermal shutdown function is not intended to replace
proper heat sinking. Activation of the thermal shutdown
circuitry is an indication of excessive power dissipation or
an inadequate heat sink. Continuously running the amplifier
into thermal shutdown can degrade reliability.
VO
OPA551
ZL
VIN
Flag
(optional)
The Thermal Shutdown Indicator (“flag”) pin can be moni-
tored to determine if shutdown is occurring. During normal
operation, the current output from the flag pin is typically
50nA. During shutdown, the current output from the flag pin
increases to 120µA (typical). This current output allows for
easy interfacing to external logic. See Figure 2 for two
examples implementing this function.
0.1µF
10µF
+
V–
FIGURE 1. Basic Circuit Connections.
VOUT
VOUT
OPA551
OPA551
VLOGIC
HP5082-2835
Flag
80µA to
160µA
+5V
Interface to virtually any CMOS
logic gate by choosing resistor
value that provides a guaranteed
logic high voltage with the
minimum (80µA) flag current. A
diode clamp to the logic supply
voltage assures that the CMOS
is not damaged by overdrive.
HCT logic has relatively well-
controlled logic level. A properly
chosen resistor value can
guarantee proper logic high level
throughout the full range of flag
output current.
HCT
CMOS
27kΩ
47kΩ
Logic
Ground
Logic
Ground
Interfacing with HCT Logic
Interfacing with CMOS Logic
FIGURE 2. Thermal Shutdown Indicator.
OPA551, OPA552
9
SBOS100A
www.ti.com
TI [ TEXAS INSTRUMENTS ]
