AS8118 View Datasheet(PDF) - austriamicrosystems AG

Part Name

Description

Manufacturer

AS8118

Single Phase Instantaneous Energy Metering IC with On-Chip Calibration, Stepper Motor Drive and LED Output

austriamicrosystems AG 

Data Sheet AS8118

For optimum operating conditions, the input signal at the Maximum Current (IMAX) condition should be set at ±30mV peak,

when the input Gain = 20, or ±150mV peak, when the input Gain = 4.

The default gain, namely the AS8118 setting which is available without any programming required, is Gain = 20.

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

=

30mVpeak

84.85Apeak

= 350µΩ

The mains current is sampled at 1.7478kHz, assuming that the recommended crystal oscillator frequency of 3.5795MHz, is

used.

Voltage Input for Energy Calculation

The voltage channel input consists of inputs VP and VN, which are is differential, with VP connected to the tap of a resistor

divider circuit of the line voltage and VN connected to Ground. For optimum operating conditions, the input signal at VP with

respect to VN, should be set at 150mV peak for the rated line voltage condition.

The maximum voltage on VP for the specified operation is 210mV with respect to VSS. The maximum allowed voltage signal

at VP, which ensures that pulses are still provided at the output, is 300mV with respect to VSS. Both VP and VN have

internal ESD protection and an over-voltage of ±7V can be sustained on these pins without risk of permanent damage to the

device.

The resistor values for an ideal voltage divider, may be calculated as follows:

Assuming a Vmains of 230V (rms) → 325V (peak) and according to the voltage divider shown below, the value for

R2 = 820Ω, the value of R1A+R1B may be calculated as follows:

Vmains

R1A+R1B

R2

Vin

R1A + R1B = R2 *

(Vmains( peak ) − VIP max )

VIP max

= 820Ω *

325V − 150mV

150mV

= 1.77MΩ

The mains voltage is sampled at 1.7478kHz, assuming that the recommended crystal oscillator frequency of 3.5795MHz is

used.

Revision 1.8, 15-Feb-05

Page 6 of 30

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