_

_

SHUNT

MAX

SHUNT

LOAD

MAX

V

100mV

R

100m

I

1A

:

(2)

amplified by the OPA992 to produce an output voltage of 0 V to 4.9 V. The gain needed by the OPA991 to

produce the necessary output voltage is calculated using Equation 3:

_

_

_

_

OUT

MAX

OUT

MIN

IN

MAX

IN

MIN

V

V

Gain

V

V

(3)

F

G

R

Gain

1

R

(4)

they are standard value resistors that create a 49:1 ratio. Other resistors that create a 49:1 ratio can also be

used. However, excessively large resistors will generate thermal noise that exceeds the intrinsic noise of the op

amp. Figure 8-2 shows the measured transfer function of the circuit shown in Figure 8-1.

8.2.1.3 Application Curve

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0

1

2

3

4

5

Figure 8-2. Low-Side, Current-Sense, Transfer Function

8.2.2 High Voltage Buffered Multiplexer

The OPAx992S shutdown devices can be configured to create a high voltage, buffered multiplexer. Outputs can

be connected together on a common bus and the shutdown pins can be used to select the desired channel to

pass through. Since the amplifier circuitry has been designed such that disable transitions occur significantly

faster than enable transitions, the amplifier naturally exhibits a "break before make" switch topology. Amplifier

outputs enter a high impedance state when placed in shutdown, so there is no risk of bus contention when

connecting multiple channel outputs together. Additionally, because outputs are isolated from inputs, there is no

concern about the impedance at the input of each channel interacting undesirably with the impedance at the

output, like an amplifier gain stage or ADC driver circuit. Also, because this topology uses amplifiers instead of

effects are eliminated.

Figure 8-3 shows an example topology for a basic 2:1 multiplexer. When SEL is low, channel 1 is selected and

active; when SEL is high, channel 2 is selected and active. For more information on how to use the OPAx992S

shutdown function, see the shutdown section in Section 6.7.

OPA992, OPA2992, OPA4992

SBOSA10 – JUNE 2021

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