OPA607 datasheet(12/21 Pages) TI1

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3.3V

1NŸ

VREF =1.24V

ADS7042

ISH

LOAD

OPA607

688 Ÿ

240 pF

GND

3.3V

20 NŸ

TLV431

RSH

OPA607

SBOS981 – OCTOBER 2019

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8.2.2 Low-Cost, High-Speed Current Sensing

Figure 7. Hi-Z, High-Speed Front-End Circuit

8.2.2.1 Design Requirements

The objective of this design is to create a high-speed, high-gain signal chain for bidirectional current-sensing

applications in power systems and motor drive systems. Detailed Design Procedure lists the design requirements

of this application.

Table 2. Design Parameters

PARAMETER

DESIGN REQUIREMENT

Amplifier and ADC supply

3.3 V

Peak current to be measured from load to ground

12 A

Peak current to be measured from ground to load

8 A

Accuracy of current measurement

0.1%

Maximum tolerable setting time

1 µs

Current sensing direction

Bidirectional

8.2.2.2 Detailed Design Procedure

The design requirements mentioned in Design Requirements help in designing the complete signal chain. The

aim of the schematic (Figure 7) is to measure bidirectional current with relatively high accuracy in a low-side-

sensing-based, high-frequency switching system.

As shown in Figure 7, a single op amp of high bandwidth is capable of accurately sensing current in a high-

frequency switching circuit along with driving the consecutive SAR ADC.

Equation 2 gives the output of the OPA607 (VOUT ) in Figure 7.

VOUT = (20 kΩ / 1 kΩ × ISH × RSH) + VREF

where

•

ISH = ISHUNT and RSH = RSHUNT

(2)

As shown Figure 7, the reference voltage applied is 1.24 V. In Equation 2, when the ISH flowing across RSH

equals zero, the output of the difference amplifier is by default biased at a voltage equal to 1.24 V.

When the current (ISH) flows from load to GND, the output of the OPA607 rises above 1.24 V with a value equal

to 20 × VSH where:

VSH = RSH × ISH

(3)

Similarly, when the current flows from GND to load (in the opposite direction) the output of the OPA607 goes

below 1.24 V with a value proportional to 20 × VSH.

The required peak current to be measured is 12 A in the first direction (load to GND).

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