STPM11 datasheet(18/43 Pages) STMICROELECTRONICS

18 / 43 page

Theory of operation

STPM11/12/13/14

18/43

7.7

Load monitoring

The STPM1X include a no-load condition detection circuit with adjustable threshold. This

circuit monitors the voltage and the current channels and, when the measured power is

below the set threshold, the internal signal BIL becomes high. The information about this

signal is also available in the status bit BIL.

The no load condition occurs when the product between VRMS and IRMS input values is

below a given value. This value can be set with the LTCH configuration bits, and it is also

dependent on the selected current gain (Ai) and the calibration registers constant Kp=Kv*Ki.

Four different no-load threshold values can be chosen according to the two configurations

bits LTCH (see

Table 11.).

When a no-load condition occurs (BIL=1), the integration of power is suspended and the

tamper module is disabled.

If a no-load condition is detected, the BIL signal blocks generation of pulses for stepper and

forces the SCLNLC pin to be low.

Figure 16.

Bandgap temperature variation

Table 11.

No load detection thresholds

LTCH

Vrms * Irms (input channel voltages)

Rogowski coil (PST<2)

Ct or Shunt (PST>1)

0.004488 / (Ai*Kp)

0.003648 / (Ai*Kp)

0.008976 / (Ai*Kp)

0.007296 / (Ai*Kp)

0.017952 / (Ai*Kp)

0.014592 / (Ai*Kp)

0.035904 / (Ai*Kp)

0.029184 / (Ai*Kp)

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