SA9109B

14/18

sames

7.

Power Failure/Battery Backup

A battery backup facility is available on VBA. This feature is provided to ensure

retention of the information stored in the registers, in case of power breaks.

The VSS supply to the analog circuitry and digital circuitry of this device has been

separated. In the event of a power failure, the supply to the analog circuitry falls

to 0V. The digital circuitry is switched to a power down mode, to minimise the supply

current from an external battery backup. During this procedure, the following

events take place:

•

All inputs are disabled

•

All outputs are placed in high impedance mode

•

The oscillator is inhibited

•

The LCD driver is disabled

•

The contents of the RAM is retained by means of an external power source.

8.

Electrostatic Discharge (ESD) Protection

The SA9109B integrated circuits inputs/outputs are protected against ESD.

9.

Power Consumption

The power consumption rating of the SA9109B integrated circuit is less than 40mW.

TYPICAL APPLICATION

In the Application Circuit (Figure 1), the components required for a single phase power

metering application are shown.

In Figure 1 a shunt resistor is used for current sensing. In the application, the circuitry

requires a +2.5V, 0V, -2.5V DC supply.

The most important external components for the SA9109B integrated circuit are:

C

converters. The value of these capacitors is 560pF.

The actual values determine signal to noise and stability performance. The tolerances

should be within ±10%.

C

The optimum value is

3.3nF. The actual values are uncritical. Values smaller than 0.5nF and larger than 5nF

should be avoided.

R

The values should be selected for an input current of 16µA

maximum line current.

R

I

L

*

R

SH

16µA

RMS

2

Where

I

L

=

Line current

RSH

=

Shunt resistor