sames

SA2102D

8/16

http://www.sames.co.za

These inputs are protected against electrostatic discharge

through clamping diodes.

The feedback loops from the outputs of the amplifiers A and A

generate virtual shorts on the signal inputs. Exact duplications

of the input currents are generated for the analog signal

processing circuitry.

IV

The current and voltage sense inputs are both identical. Both

inputs are differential current driven up to ±25µA peak. One

input of the voltage sense amplifier is internally connected to

AGND. This is possible because the voltage sense input is

much less sensitive to externally induced parasitic signals

compared to the current sense inputs.

The power consumption of the SA2102D integrated circuit is

less than 25mW.

A bias resistor of 47k

sets optimum bias and reference

conditions on chip. Calibration of the SA2102D should be done

on the voltage input as described in the Typical Application

section and not on the Vref input.

Figure 6 shows the typical connections for the current sensor

input. The resistor R1 and R2 define the current level into the

current sense inputs of the SA2102D. At Maximum Rated

Mains current (I

) the resistor values should be selected for

an input current of 16µA

.

POWER CONSUMPTION

INPUT SIGNALS

Voltage Reference (VREF)

Current sense input (IIP and IIN)

W

MAX

RMS

The values for resistors R1 and R2 can be calculated as

follows:

R1 = R2 = (I /16µA) x RSH/2

Where I

=

Line current

RSH

=

Shunt resistor or termination

resistor if a CT is used as the current sensor.

The value of RSH, if used as the CT's termination resistor,

should be less than the DC resistance of the CT's secondary

winding. The voltage drop across RSH should not be less

than 20mV

at I

The current into the A/D converter should be set at 14µA

at

Nominal Mains Voltage (V

).

The voltage sense input saturates at an input

current of ±25µA peak. Referring to Figure 6 the typical

connections for the voltage sense input is illustrated.

Resistors R3, R4 and R5 set the current for the voltage sense

input. The Nominal Mains Voltage is divided down to 14V

.

The current into the A/D converter input is set at 14µA

via

resistor R5 of value 1M

L

L

RMS

RMS

NOM

RMS

RMS

MA

X

Voltage Sense Input (IVP)

This is to allow a variation of

±10% for the mains voltage without saturating the voltage

sense input.

The FAST pin is used to select between STANDARD and

FAST mode. Leaving this pin open or connecting to Vss

enables the STANDARD mode and connecting to Vdd

enables FAST mode.

When STANDARD mode is enabled the LED output pulses at

a low frequency. This low frequency allows a longer

accumulation period and the output pulses are therefore

proportional to the average power consumption measured.

The Rated Select Condition pins (R0,R1 andR2) are used to

select different LED output frequencies which in turn selects

the applications meter constant. Refer to figure 8 for the LED

output timing diagram in STANDARD mode.

When the FAST mode is enabled the LED output generates

pulses at a frequency of 1160Hz at I

and V

. In this

mode the pulse frequency is proportional to the

instantaneous power consumption measured. This mode is

used for meter calibration purposes and can also be used

when interfacing to a microcontroller. Refer to figure 9 for the

LED output timing diagram in FAST mode.

W.

Fast Mode Select (FAST)

MAX

NOM

Figure 6: Application circuit

VDD

VDD

Supply

Supply

N

L

PULSES

REVERSE

VDD

IIN

R1

R2

R5

R3

R4

P1

IIP

IVP

AGND

VSS FAST

R0 R1 R2

VREF

LOAD

DR-01568

L

N

LED

MOP

SA2102D

8888888

MON

DIRO DIRI

SO

Rsh