ADE7755

Rev. A | Page 14 of 20

Channel 2 (Voltage Channel)

The output of the line voltage transducer is connected to the

ADE7755 at this analog input. Channel 2 is a fully differential

voltage input. The maximum peak differential signal on Channel 2

is ±660 mV. Figure 25 illustrates the maximum signal levels that

can be connected to Channel 2 of the ADE7755.

+660mV

–660mV

V2

DIFFERENTIAL INPUT

±660mV MAX PEAK

COMMON-MODE

±100mV MAX

V2P

V2N

V2

AGND

Figure 25. Maximum Signal Levels, Channel 2

Channel 2 must be driven from a common-mode voltage, that

is, the differential voltage signal on the input must be referenced

to a common mode (usually AGND). The analog inputs of the

ADE7755 can be driven with common-mode voltages of up to

100 mV with respect to AGND. However, best results are achieved

using a common mode equal to AGND.

TYPICAL CONNECTION DIAGRAMS

Figure 26 shows a typical connection diagram for Channel 1. A

current transformer (CT) is the current transducer selected for

this example. Note that the common-mode voltage for Channel 1

is AGND and is derived by center-tapping the burden resistor to

AGND. This provides the complementary analog input signals for

V1P and V1N. The CT turns ratio and burden resistor Rb are

selected to give a peak differential voltage of ±470 mV/gain at

maximum load.

V1P

AGND

±470mV

GAIN

Rb

Rf

Rf

CT

NEUTRAL

PHASE

IP

V1N

Cf

Cf

Figure 26. Typical Connection for Channel 1

Figure 27 shows two typical connections for Channel 2. The first

option uses a potential transformer (PT) to provide complete

isolation from the power line. In the second option, the ADE7755

is biased around the neutral wire, and a resistor divider provides

a voltage signal that is proportional to the line voltage. Adjusting

the ratio of Ra, Rb, and VR is also a convenient way of carrying

out a gain calibration on the meter.

±660mV

V2P

AGND

Rf

Rf

PT

NEUTRAL

PHASE

V2N

Cf

Cf

±660mV

V2P

Rf

NEUTRAL

PHASE

V2N

Cf

Cf

Rb + VR = Rf

Figure 27. Typical Connections for Channel 2

POWER SUPPLY MONITOR

The ADE7755 contains an on-chip power supply monitor. The

If the supply is less than 4 V ± 5%, the ADE7755 resets. This is

useful to ensure correct device startup at power-up and power-

down. The power supply monitor has built-in hysteresis and

filtering. These features give a high degree of immunity to false

triggering due to noisy supplies.

In Figure 28, the trigger level is nominally set at 4 V. The

tolerance on this trigger level is about ±5%. The power supply

and decoupling for the part should be such that the ripple at

operation.

5V

4V

0V

TIME

RESET

ACTIVE

RESET

INTERNAL

RESET

Figure 28. On-Chip Power Supply Monitor