OPA186DBVT datasheet(28/48 Pages) TI1

28 / 48 page

Lastly, some notes about maximizing the high-side current monitor performance:

• All resistor values are critical for accurate gain results. Match resistor pairs of [R1 and R3] and [R2 and R4]

as closely as possible to minimize common-mode mismatch error. Use a 0.1% tolerance, or better. Often,

selecting two adjacent resistors on a reel provides close matching compared to random selection.

• Keep the closed-loop gain, GA, of the OPAx186 difference amplifier set to a reasonable value to reduce gain

error and maximize bandwidth. A GA of 30 V/V is used in the example.

• Although current monitoring is often used for monitoring dc supply currents, ac current can also be monitored.

The –3-dB bandwidth, or upper cutoff frequency, of the circuit is:

GBW

Noise Gain

(4)

where

• GBW = the amplifier unity gain bandwidth; 750 kHz for the OPAx186.

• Noise Gain = the gain as seen going into the op-amp noninverting input, and is defined by:

(5)

For the OPAx186 circuit in Figure 8-3, the results are:

30 k

1 k

750 kHz

24.2 kHz

(6)

Make sure that the amplifier slew rate is sufficient to support the expected output voltage swing range and

waveform. Also, if a single power supply (such as 24 V) is used, the ac power source applied to the sense input

must have a positive dc component to keep the VCM greater than 0 V. To maintain normal operation, the input

voltage cannot drop to less than 0 V.

The OPAx186 output can attain a 0

‑V output level if a small negative voltage is used to power the V– pin

instead of ground. The LM7705 is a switched capacitor voltage inverter with a regulated, low-noise, –0.23-V

fixed voltage output. Powering the OPAx186 V– pin at this level approximately matches the 300

‑mV linear output

voltage swing lower limit, thus extending the output swing to 0 V, or very near 0 V. This configuration greatly

improves the resolution at low sense current levels.

The LM7705 requires only about 78 μA of quiescent current, but be aware that the specified supply range is 3 V

to 5.25 V. The 3.3-V or 5-V supply used by the ADC can be used as a power source.

For more information about amplifier-based, high-side current monitors, see the TI Analog Engineer’s Circuit

Cookbook: Amplifiers.

OPA186, OPA2186, OPA4186

SBOS968C – JUNE 2022 – REVISED JULY 2023

www.ti.com

Submit Document Feedback

Product Folder Links: OPA186 OPA2186 OPA4186

OPA186DBVT датащи(PDF) 28 Page - Texas Instruments