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AS8002

Data Sheet - A p p l i c a t i o n I n f o r m a t i o n

8 Application Information

Table 30 provides examples of Gain selection of Channel 1 for different shunt resistors and maximum RMS currents.

8.1 Application Hints

pinned out to minimize coupling between the analog and digital sections of the device. The printed circuit board (PCB) that houses the AS8002

should be designed such that the analog and digital sections are separated and confined to certain areas on the board. This design facilitates the

use of ground planes that can be easily separated.

To provide optimum shielding for ground planes, a minimum etch technique is generally best. All VSS pins of the AS8002 should be sunk in the

ground plane. Digital and analog ground planes should be joined in only one spot. If the AS8002 is in a system where multiple devices require an

AVSS and DVSS connection, this connection should still be made at one point only; a star ground point that should be established as close as

possible to the ground pins on the AS8002.

Avoid running digital lines under the device as this couples noise into the chip. However, the analog ground plane should be allowed to run under

the AS8002 to avoid noise coupling. The power supply lines to the AS8002 should use as large trace width as possible to provide low impedance

paths and reduce the effects of glitches on the power supply line.

Likewise, the positive supply pins AVDD and DVDD should be connected only at one common star point close the output of the power supply.

For best performance of the analog blocks of the AS8002, it is important to have a clean, noise-free supply voltage at AVDD.

To avoid radiating noise to other sections of the board, fast switching signals, such as clocks, should be shielded with digital ground, and clock

signals should never run near the analog inputs. Avoid crossover of digital and analog signals. To reduce the effects of feedthrough within the

board, traces on opposite sides of the board should run at right angles to each other. A microstrip technique is the best method but is not always

possible with a double sided board. In this technique, the component side of the board is dedicated to ground planes, while signals are placed on

the opposite side.

Good decoupling is also important. All analog supplies should be decoupled with 10µF ceramic capacitors in parallel with 0.1µF capacitors to

GND. Refer to Typical Application Circuit (page 9). To achieve the best results from these decoupling components, they must be placed as close

as possible to the device The 0.1µF capacitors should have low effective series resistance (ESR) and low effective series inductance (ESI), such

as common ceramic types or surface-mount types. These low ESR and ESI capacitors provide a low impedance path to ground at high

frequencies to handle transient currents due to internal logic switching.

Table 30. Gain Selection

Shunt Resistor Value

Sensing RMS Current (A)

Recommended Linear Gain for Channel 1 for

ADC to work in 80% of dynamic range

7.5 m

Ω

1.5

Gain1 = 64

10 m

Ω

1.5

Gain1 = 48

5 m

Ω

3

Gain1 = 48

7.5 m

Ω

3

Gain1 = 32

10 m

Ω

3

Gain1 = 24

5 m

Ω

6

Gain1 = 24

7.5 m

Ω

6

Gain1 = 16

10 m

Ω

6

Gain1 = 12