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AD7147

Rev. 0 | Page 31 of 68

OUTPUTS

ACSHIELD OUTPUT

The AD7147 measures capacitance between CINx and ground.

Any capacitance to ground on the signal path between the CINx

pins and the sensor is included in the AD7147 conversion result.

To eliminate stray capacitance to ground, the ACSHIELD signal should

be used to shield the connection between the sensor and CINx,

as shown in Figure 46. The plane around the sensors should also

be connected to ACSHIELD.

CIN0

CIN1

CIN2

CIN3

ACSHIELD

AD7147

Figure 46. ACSHIELD

The ACSHIELD output is the same signal waveform as the

excitation signal on CINx. Therefore, there is no ac current

between CINx and ACSHIELD, and any capacitance between these

pins does not affect the CINx charge transfer.

Using ACSHIELD eliminates capacitance-to-ground pickup, which

means that the AD7147 can be placed up to 60 cm away from

the sensors. This allows the AD7147 to be placed on a separate

PCB than that of the sensors if the connections between the

sensors and the CINx inputs are correctly shielded using

ACSHIELD.

GPIO

The AD7147 has one GPIO pin. It can be configured as an input or

an output. The GPIO_SETUP Bits [13:12] in the interrupt enable

Table 16. GPIO_SETUP Bits

GPIO_SETUP

GPIO Configuration

GPIO disabled

Input

Output low

Output high

When the GPIO is configured as an output, the voltage level on

the pin is set to either a low level or a high level, as defined by

the GPIO_SETUP bits (see Table 16).

The GPIO_INPUT_CONFIG bits in the interrupt enable

the GPIO pin when the GPIO is configured as an input. The

GPIO can be configured as either active high or active low, as

well as either edge triggered or level triggered (see Table 17).

Table 17. GPIO_INPUT_CONFIG Bits

GPIO_INPUT_CONFIG

GPIO Configuration

Triggered on negative level (active low)

Triggered on positive edge (active high)

Triggered on negative edge (active low)

Triggered on positive level (active high)

When GPIO is configured as an input, it triggers the interrupt

output on the AD7147. Table 15 lists the interrupt output

behavior for each of the GPIO configuration setups.

USING THE GPIO TO TURN ON/OFF AN LED

The GPIO on the AD7147 can be used to turn on and off an

LED by setting the GPIO as either output high or low. Setting

the GPIO output high turns on the LED; setting the GPIO

output low turns off the LED. The GPIO pin connects to a

transistor that provides the drive current for the LED. Suitable

transistors include the KTC3875 from Korea Electronics Co.,

Ltd. (KEC).

AD7147

GPIO

VCC

KTC3875

OR SIMILAR

Figure 47. Controlling an LED Using the GPIO

AD7147 Datasheet(PDF) 31 Page - Analog Devices

AD7147 Datasheet(HTML) 31 Page - Analog Devices

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