Datasheet

OPA547
9
SBOS056F
www.ti.com
ducting output transistor. Power dissipation can be mini-
mized by using the lowest possible power-supply voltage
necessary to assure the required output voltage swing.
For resistive loads, the maximum power dissipation occurs at
a dc output voltage of one-half the power-supply voltage.
Dissipation with ac signals is lower. Application Bulletin
SBOA022 explains how to calculate or measure power
dissipation with unusual signals and loads.
HEAT SINKING
Most applications require a heat sink to assure that the
maximum junction temperature (150°C) is not exceeded. The
heat sink required depends on the power dissipated and on
ambient conditions. Consult Application Bulletin SBOA021 for
information on determining heat sink requirements. The inter-
nal protection circuitry was designed to protect against over-
load conditions. It does not activate until the junction tempera-
ture reaches approximately 160°C and was not intended to
replace proper heat sinking. Continuously running the OPA547
into thermal shutdown will degrade reliability.
The tab of the DDPAK surface-mount version should be
soldered to a circuit board copper area for good heat dissi-
pation. Figure 4 shows typical thermal resistance from junc-
tion to ambient as a function of the copper area.
FIGURE 4. Thermal Resistance versus Circuit Board Copper Area.
THERMAL RESISTANCE vs
CIRCUIT BOARD COPPER AREA
50
40
30
20
10
0
Thermal Resistance, θ
JA
(°C/W)
012345
Copper Area (inches
2
)
OPA547F
Surface-Mount Package
1oz copper
Circuit Board Copper Area
OPA547
Surface-Mount Package
FIGURE 3. Adjustable Current Limit.
31.6kΩ
R
CL
0.01µF
(optional, for noisy
environments)
3
4
3
4
4.75V
G = 5000
R
CL
= – 31.6kΩ
OPA547 CURRENT LIMIT: 0mA to 750mA
NOTE: (1) Resistors are nearest standard 1% values.
DESIRED
CURRENT LIMIT
0mA
100mA
375mA
500mA
750mA
RESISTOR
(1)
(R
CL
)
I
LIM
Open
205kΩ
31.6kΩ
15.8kΩ
I
LIM
Shorted to V–
CURRENT DAC
(I
DAC
)
0µA
20µA
75µA
100µA
150µA
VOLTAGE DAC
(V
DAC
)
(V–) + 4.75V
(V–) + 4.12V
(V–) + 2.38V
(V–) + 1.59V
(V–) + 0.01V
RESISTOR METHOD
5000 (4.75V)
I
LIM
V–
V
O
31.6kΩ
4.75V
G = 5000
I
DAC
= I
LIM
/5000
V
DAC
= (V–) + 4.75V – (31.6kΩ) (I
LIM
)/5000
DAC METHOD (Current or Voltage)
V–
V
O
D/A