Datasheet

OPA547
12
SBOS056F
www.ti.com
VOLTAGE SOURCE APPLICATION
Figure 12 illustrates how to use the OPA547 to provide an
accurate voltage source with only three external resistors.
First, the current limit resistor, R
CL
, is chosen according to
the desired output current. The resulting voltage at the I
LIM
pin is constant and stable over temperature. This voltage,
V
CL
, is connected to the noninverting input of the op amp and
used as a voltage reference, thus eliminating the need for an
external reference. The feedback resistors are selected to
gain V
CL
to the desired output voltage level.
FIGURE 13. Resistor-Controlled Programmable Power Supply.
FIGURE 12. Voltage Source.
31.6kΩ
R
CL
I
LIM
0.01µF
(Optional, for noisy
environments)
4.75V
I
O
=
5000 (4.75V)
31.6kΩ + R
CL
V
O
= V
CL
(1 + R
2
/R
1
)
V–
V+
V
CL
V
CL
= = 2.375V
Desired V
O
= 19V,
R
1
= 1kΩ and R
2
= 7kΩ
G = = 8
19
2.375
For Example:
31.6kΩ • 4.75V
(31.6kΩ + 31.6kΩ)
If I
LIM
= 375mA, R
CL
= 31.6kΩ
R
2
R
1
Uses voltage developed at I
LIM
pin
as a moderately accurate reference
voltage.
PROGRAMMABLE POWER SUPPLY
A programmable power supply can easily be built using the
OPA547. Both the output voltage and output current are
user-controlled. Figure 13 shows a circuit using potentiom-
eters to adjust the output voltage and current while Figure 14
uses DACs. An LED tied to the E/S pin through a logic gate
indicates if the OPA547 is in thermal shutdown.
G = 1 + = 10
9kΩ
1kΩ
9kΩ1kΩ
OPA547
+30V
+5V
+5V
0.8V to 2.5V
0V to 4.75V
Output
Adjust
V+
5
6
Thermal
Shutdown Status
NOTES: (1) For V
O
= 0V, V– = –1V.
(2) Optional: Improves noise
immunity.
(LED)
74HCT04
R ≥ 250Ω
E/S
V
O
= 0.8V to 25V
(1)
7
4
3
1
2
V–
I
LIM
14.7kΩ
4.7kΩ
Current
Limit
Adjust
1kΩ
20kΩ
0.01µF
(2)