AS8218BLQS Ver la hoja de datos (PDF) - austriamicrosystems AG

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Fabricante

AS8218BLQS

Highly Integrated Single Phase 2-Current Energy Metering Integrated Circuits with Microcontroller, RTC, Programmable Multi-Purpose I/Os and LCD Driver

austriamicrosystems AG 

Data Sheet AS8218 / AS8228

The current input signal levels may be programmed by means of on-chip programmable gain settings. The

required gain setting is selected as follows:

Current Input Gain Settings

Gain Input Voltage

Current Inputs I1P, I1N

20

-30mV≤VI1P≤30mV

16

-38mV≤VI1P≤38mV

4

-150mV≤VI1P≤150mV

Current Inputs I2P, I2N

20

-30mV≤VI2P≤30mV

16

-38mV≤VI2P≤38mV

4

-150mV≤VI2P≤150mV

Comments

Shunt mode; default setting

CT mode or shunt mode

CT mode

Shunt mode

CT mode or shunt mode

CT mode; default setting

Notes:

1) VI1N and VI2N are connected to VSSA.

2) Refer to the Settings Register (SREG) in the DSP section for programming of the Gain Settings.

For optimum operating conditions, the input signal at the Maximum Current (Imax) condition should be set at

±30mVp, when the Gain = 20, or ±150mVp, when the Gain = 4.

The default Gain, the AS8218 / AS8228 ICs current input gain settings without any programming required, is

Gain = 20 for the I1 input and Gain = 4 for the I2 input.

The value of an ideal shunt resistor, may be calculated as follows:

Assuming an Imax rating of 60A (rms) → 84.85A (peak), then a shunt value of 350µΩ would be suitable.

Rshunt

=

30mVp

84.85Ap

= 354μΩ

thus a standard 300µΩ shunt resistor may be selected.

The mains currents are sampled at 3.4956kHz, assuming that the recommended crystal oscillator frequency of

3.5795MHz, is used.

The current transformer(s) must be terminated with a voltage setting resistor (RVS) to ensure the optimum

voltage input level to the current input(s) of the AS8218 / AS8228 ICs. The value of RVS is calculated as

follows:

R VS = Vin(p)

IL 2

where

IL

Vin(p)

= CT RMS secondary current at rated conditions (Vmains; Imax)

= The peak input voltage to the IC at rated conditions (Vmains; Imax). For example, if Gain = 4,

Vin(p) should be set at 150mVpeak.

Example: A current transformer is specified at 60A/24mA and the Gain = 4:

Revision 3.0, 31-May-06

Page 17 of 123

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