sames

PM2005M/P

6/12

http://www.sames.co.za

http://www.sames.co.za

POWER SUPPLY

PCB DESIGN

Referring to figure 9, capacitor C10 is charged through D2

during the positive half of the sine wave from the R29, C12

mains voltage dropper. Identical charging circuitry exists for

the other two phases. During the negative sine wave, C11 is

charged through diode D1. The unregulated voltage charged

on C10 and C11 is limited to 47 V by means of zener diode D7.

Resistors R32 and R33 act as current limiting resistors that

feed the unregulated voltage to the positive and negative

voltage regulators U3 and U4. The voltage regulators need a

load capacitance of around 10µF (C8 and C9) to be in a stable

operating region. C15 acts as a supply voltage storage

capacitor.

Jumpers J4, J5 and J7 allow the power supply to be completely

disconnected form the metering section from the device.

The module represents a Class 1 meter that is designed to

demonstrate the functionality and performance of the

SA2005M or SA2005P metering circuits. The SA2005M/P is

single chip solution for a three-phase meter that drives a

mechanical counter. When the meter PCB is designed, it

should be taken into account that the SA2005 is a mixed signal

integrated circuit and special care should to be taken with the

power supply and signal routing to the device.

The SA2005 should be protected from its measuring

environment. This is achieved by using resistor dividers to

scale all the SA2005 input signals. MOV's Z1, Z2, Z3 together

with resistors R29, R30, R31 protects the power supply

capacitors. The current setting resistors on the current sense

inputs of the device attenuates common mode and

asymmetrical transients.

All the resistors connecting to the SA2005's current sense

Protection

Component placement

inputs should be placed as close as possible to the SA2005.

This eliminates the possibility of any stray signal coupling into

the divided input signal.

The GND pin of the SA2005 is connected to the neutral phase,

which is halfway between VDD and VSS. Note that supply

bypass capacitors C4 and C5 are positioned as close as

possible to the supply pins of the SA2005, and connected to a

solid ground plane. Capacitor C6 is positioned as close as

possible to the supply pins of the device for proper supply

bypassing.

The 5V supply is de-coupled and routed directly to the power

pins of the IC by means of capacitor C5. Care is taken not to

have current flowing in the node that connects the voltage

reference resistor to VSS as it may introduce power supply

noise on the voltage reference circuit.

Most of the signal routing is done in such a manner that any

signal coupling in to the measured signal will be a common

mode noise signal and is rejected subsequently. Care should

be taken that the signals to the SA2005 is not influenced by

other sources such as transformers with electric fields

coupling in to the signals.

Calibration can be done by adjusting the trimpots (P1, P2, P3)

connected to the three voltage inputs.

Ground Plane

Power Supply routing and de coupling

Signal Routing

Calibration

10

20

30

40

60

80

230

230

230

230

230

230

PH/DIR

PH/DIR

VDD

PH/DIR

VDD

PH/DIR

PH/DIR or VDD

PH/DIR or VDD

PH/DIR or VDD

VSS or Open

VSS or Open

VSS or Open

VDD

VDD

VDD

VDD

VDD

VDD

3200

1600

1600

3200

3200

1600

800

400

400

200

200

100

Motor Pulse

Rate (Pulses/kWh)

LED Pulse rate

(Pulses/kWh)

IM

RE

RA

Vmax

Imax