71M6511 Datasheet, PDF (81/95 Pages) Teridian Semiconductor Corporation – Single-Phase Energy Meter IC

71M6511/71M6511H
Single-Phase Energy Meter IC
DATA SHEET
AUGUST 2007
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 37 shows the basic connections. The OPT_TX pin becomes active when the I/O RAM register OPT_TXDIS is set to 0.
V3P3
71M6511
OPT_RX
100pF 100kΩ
R₁
Phototransistor
OPT_TX
R₂
LED
V3P3
Figure 37: 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 38. A shorting
jumper on this header pulls V1 up to V3P3, disabling the hardware watchdog timer. C1 helps suppressing ESD.
R₁
R₃
10kΩ
V_in
R₂
C₁
V1
100pF
Figure 38: 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 39. R₁ should be in the range of 200Ω, R₂ should be around 10Ω. The capacitor C₁ 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, R₂ can be removed.
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