Datasheet

71M6511/71M6511H
Single-Phase Energy Meter IC
DATA SHEET
NOVEMBER 2010
Page: 83 of 98 © 2005–2010 Teridian Semiconductor Corporation V2.7
A Maxim Integrated Products Brand
Optical Interface
The pins OPT_TX and OPT_RX can be used for a regular serial interface, e.g. by connecting a RS_232 transceiver, or they
can be used to directly operate optical components, e.g. an infrared diode and phototransistor implementing a FLAG interface.
Figure 35 shows the basic connections. The OPT_TX pin becomes active when the I/O RAM register OPT_TXDIS is set to 0.
OPT_TX
R
2
R
1
OPT_RX
71M6511
V3P3
Phototransistor
LED
100kΩ
100pF
V3P3
OPT_TX
R
2
R
1
OPT_RX
71M6511
V3P3
Phototransistor
LED
100kΩ
100pF
V3P3
Figure 35: Connection for Optical Components
Connecting V1 and Reset Pins
A voltage divider should be used to establish a safe range for V1 when the meter is in mission mode (V1 must be lower than
2.9V in all cases in order to keep the hardware watchdog timer enabled). For proper debugging or loading code into the
71M6511 mounted on a PCB, it is necessary to have a provision like the header shown above R1 in Figure 36. A shorting
jumper on this header pulls V1 up to V3P3, disabling the hardware watchdog timer. C1 helps suppressing ESD.
V
in
R
2
V1
R
1
R
3
10kΩ
C
1
100pF
V
in
R
2
V1
R
1
R
3
10kΩ
C
1
100pF
Figure 36: Voltage Divider for V1
Even though a functional meter will not necessarily need a reset switch, it is useful to have a reset pushbutton for prototyping.
When a circuit is used in an EMI environment, the RESETZ pin should be supported by the external components shown in
Figure 37. R
1
should be in the range of 200Ω, R
2
should be around 10Ω. The capacitor C
1
should be 1nF. R1 and C1 should
be mounted as close as possible to the IC. In cases where the trace from the pushbutton switch to the RESETZ pin poses a
problem, R
2
can be removed.