90E21 datasheet(13/57 Pages) IDT

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90E21/22/23/24

SINGLE-PHASE HIGH-PERFORMANCE WIDE-SPAN ENERGY METERING IC

Functional Description

January 10, 2012

3.4

N LINE METERING AND ANTI-TAMPERING

3.4.1

METERING MODE AND L/N LINE CURRENT SAMPLING

GAIN CONFIGURATION

The 90E23 and 90E24 have two current sampling circuits with N line

metering and anti-tampering functions. The MMD1 and MMD0 pins are

used to configure the metering mode. Refer to Table-7.

The 90E23 and 90E24 have two current sampling circuits with differ-

ent gain configurations. L line gain can be 1, 4, 8, 16 and 24, and N line

gain can be 1, 2 and 4. The configuration is made by the MMode register

(2BH). Generally L line can be sampled over shunt resistor or CT. N line

can be sampled over CT for isolation consideration. Note that Rogowski

coil is not supported.

3.4.2

ANTI-TAMPERING MODE

Threshold

In anti-tampering mode, the power difference threshold between L

line and N line can be: 1%, 2%,... 12%, 12.5%, 6.25%, 3.125% and

1.5625%, altogether 16 choices. The configuration is made by the

Pthresh[3:0] bits (MMode, 2BH) and the default value is 3.125%. The

threshold is applicable for active energy. The metering line of the reac-

tive energy follows that of the active energy.

Compare Method

In anti-tampering mode, the compare method is as follows:

If current metering line is L line and

N line is switched as the metering line, otherwise L line keeps as the

metering line.

If current metering line is N line and

L line is switched as the metering line, otherwise N line keeps as the

metering line.

This method can achieve hysteresis around the threshold automati-

cally. L line is employed after reset by default.

Special Treatment at Low Power

When power is low, general factors such as the quantization error or

calibration difference between L line and N line might cause the power

difference to be exceeded. To ensure L line and N line to start up nor-

mally, special treatment as follows is adopted:

The line with higher power is selected as the metering line when both

L line and N line power are lower than 8 times of the startup power but

higher than the startup power.

Table-7 Metering Mode

MMD1 MMD0

Metering Mode

CFx (CF1 or CF2) Output

Anti-tampering

Mode

(larger power)

CFx represents the larger energy

line. Refer to section 3.4.2.

L Line Mode (fixed L line)

CFx represents L line energy all

the time.

L+N Mode (applicable for

single-phase

three-wire

system)

CFx represents the arithmetic

sum of L line and N line energy

Flexible Mode (line speci-

fied by the LNSel bit

(MMode, 2BH))

CFx represents energy of the

specified line.

Threshold

100%

Power

Active

Line

Power

Active

Line

Power

Active

Line

Threshold

100%

Power

Active

Line

Power

Active

Line

Power

Active

Line

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