71m6521be Maxim Integrated Products, Inc., 71m6521be Datasheet - Page 65

• Manufacturer Part Number: 71m6521be
• Description: Energy Meter Ic
• Manufacturer: Maxim Integrated Products, Inc.

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.
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. R
to the IC.
V1.0
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.
GND
GND
V3P3
V3P3
71M6521BE
71M6521BE
Figure 34: Connection for Optical Components
© 2005-2008 TERIDIAN Semiconductor Corporation
OPT_RX
OPT_RX
OPT_TX
OPT_TX
Connecting V1 and Reset Pins
Figure 35: Voltage Divider for V1
R
R
100pF
100pF
1
1
R
R
1
2
2
should be in the range of 100Ω and mounted as closely as possible
10kΩ
10kΩ
R
R
2
2
V3P3SYS
V3P3SYS
5kΩ
5kΩ
R
R
Phototransistor
Phototransistor
LED
LED
R
R
1
1
3
3
100pF
100pF
C
C
V3P3SYS
V3P3SYS
1
1
Energy Meter IC
V1
V1
71M6521BE
DATA SHEET
JANUARY 2008
Page: 65 of 97