OP291GS Analog Devices Inc, OP291GS Datasheet - Page 20

• Manufacturer Part Number: OP291GS
• Description: IC OPAMP GP R-R 3MHZ DUAL 8SOIC
• Manufacturer: Analog Devices Inc

Specifications of OP291GS

• Rohs Status: RoHS non-compliant
• Amplifier Type: General Purpose
• Number Of Circuits: 2
• Output Type: Rail-to-Rail
• Slew Rate: 0.5 V/µs
• Gain Bandwidth Product: 3MHz
• Current - Input Bias: 30nA
• Voltage - Input Offset: 80µV
• Current - Supply: 260µA
• Current - Output / Channel: 16mA
• Voltage - Supply, Single/dual (±): 2.7 V ~ 12 V, ±1.35 V ~ 6 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• -3db Bandwidth: -

OP191/OP291/OP491
A 2.5 V REFERENCE FROM A 3 V SUPPLY
In many single-supply applications, the need for a 2.5 V
reference often arises. Many commercially available monolithic
2.5 V references require a minimum operating supply voltage of
4 V. The problem is exacerbated when the minimum operating
system supply voltage is 3 V. The circuit illustrated in Figure 67
is an example of a 2.5 V reference that operates from a single
3 V supply. The circuit takes advantage of the OP291 rail-to-rail
input and output voltage ranges to amplify an AD589 1.235 V
output to 2.5 V. The OP291 low TCV
maintain an output voltage temperature coefficient of less than
200 ppm/°C. The circuit overall temperature coefficient is
dominated by the temperature coefficient of R2 and R3. Lower
temperature coefficient resistors are recommended. The entire
circuit draws less than 420 μA from a 3 V supply at 25°C.
AD589
5 V ONLY, 12-BIT DAC SWINGS RAIL-TO-RAIL
The OPx91 family is ideal for use with a CMOS DAC to
generate a digitally controlled voltage with a wide output range.
Figure 68 shows the DAC8043 used in conjunction with the
AD589 to generate a voltage output from 0 V to 1.23 V. The
DAC is operated in voltage switching mode, where the reference
is connected to the current output, I
is taken from the V
noninverting as opposed to the classic current output mode,
which is inverting and, therefore, unsuitable for single supply.
AD589
17.8kΩ
17.4kΩ
1.23V
R1
R1
Figure 67. A 2.5 V Reference that Operates on a Single 3 V Supply
3V
3
100kΩ
R3
I
Figure 68. 5 V Only, 12-Bit DAC Swings Rail-to-Rail
OUT
GND CLK SR1
V
DAC8043
5V
4
DD
3
2
100kΩ
8
OP291
REF
R2
7
CONTROL
232Ω
1/2
DIGITAL
3V
1%
4
R3
8
pin. This topology is inherently
6
5kΩ
V
R1
R
1
REF
LD
32.4kΩ
FB
5
1%
R2
2
1
RESISTORS = 1%, 100ppm/°C
POTENTIOMETER = 10 TURN, 100ppm/°C
3
2
OUT
2.5V
OP291
OS
1/2
, and the output voltage
5V
REF
of 1 μV/°C helps
8
4
100kΩ
1%
R4
1
V
OUT
= –––– (5V)
4096
D
Rev. E | Page 20 of 24
The OP291 serves two functions. First, it is required to buffer
the high output impedance of the DAC V
order of 10 kΩ. The op amp provides a low impedance output
to drive any following circuitry. Second, the op amp amplifies
the output signal to provide a rail-to-rail output swing. In this
particular case, the gain is set to 4.1 to generate a 5.0 V output
when the DAC is at full scale. If other output voltage ranges are
needed, such as 0 V to 4.095 V, the gain can easily be adjusted
by altering the value of the resistors.
A HIGH-SIDE CURRENT MONITOR
In the design of power supply control circuits, a great deal of
design effort is focused on ensuring a pass transistor’s long-
term reliability over a wide range of load current conditions.
As a result, monitoring and limiting device power dissipation
is of prime importance in these designs. The circuit illustrated
in Figure 69 is an example of a 5 V, single-supply, high-side
current monitor that can be incorporated into the design of a
voltage regulator with fold-back current limiting or a high
current power supply with crowbar protection. This design uses
an OP291 rail-to-rail input voltage range to sense the voltage
drop across a 0.1 Ω current shunt. A p-channel MOSFET used
as the feedback element in the circuit converts the op amp
differential input voltage into a current. This current is then
applied to R2 to generate a voltage that is a linear representation
of the load current. The transfer equation for the current
monitor is given by
For the element values shown, the monitor output transfer
characteristic is 2.5 V/A.
Monitor
MONITOR
OUTPUT
Figure 69. A High-Side Load Current Monitor
Output
5V
2.49kΩ
3N163
100Ω
R2
M1
R1
S
=
D
R
2
×
R
G
⎛
⎜
⎝
0.1Ω
SENSE
R
SENSE
R
1
⎞
× ⎟
⎠
I
L
3
2
REF
OP291
I
L
1/2
pin, which is on the
4
8
5V
1
5V