71M6521BE
Energy Meter IC
DATA SHEET
JANUARY 2008
V3P3SYS
R1
71M6521BE
10kΩ
100pF
OPT_RX
Phototransistor
V3P3SYS
LED
R2
OPT_TX
Figure 34: Connection for Optical Components
Connecting V1 and Reset Pins
A voltage divider should be used to establish that V1 is in a safe range 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
71M6521BE mounted on a PCB, it is necessary to have a provision like the header shown above R1 in Figure 35. A shorting
jumper on this header pulls V1 up to V3P3 disabling the hardware watchdog timer.
The parallel impedance of R1 and R2 should be approximately 20 to 30kΩ in order to provide hysteresis for the power fault
monitor.
R1
R3
V3P3
GND
5kΩ
V1
C1
100pF
R2
Figure 35: 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,
as shown in Figure 36, left side. The RESET signal may be sourced from V3P3SYS (functional in MISSION mode only),
V3P3D (MISSION and BROWNOUT modes), VBAT (all modes, if battery is present), or from a combination of these sources,
depending on the application. When the 71M6521BE is used in an EMI environment, the RESET pin should be protected by
the external components shown in Figure 36, right side. R1 should be in the range of 100Ω and mounted as closely as possible
to the IC.
Since the 71M6521BE generates its own power-on reset, a reset button or circuitry, as shown in Figure 36, left side, is
only required for test units and prototypes.
V1.0
© 2005-2008 TERIDIAN Semiconductor Corporation
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